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Summary of Contents

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    Advanced ConcreteTechnology

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    Advanced ConcreteTechnologyZongjin LiJOHN WILEY & SONS, INC.

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    This book is printed on acid-free paper.Copyright 2011 by John Wiley & Sons, Inc. All rights reservedPublished by John Wiley & Sons, Inc., Hoboken, New JerseyPublished simultaneously in CanadaNo part of this publication may be reproduced, stored in a retrieval system, or transmitted in...

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    To students, teachers, researchers, and engineers in the field of concrete, who are the driving forcesfor the development of the science and technology of concrete, including the personnel workingon the China 973 project, Basic Study on Environmentally Friendly Contemporary Concrete(2009CB623200).

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    CONTENTSPrefacexi1Introduction to Concrete11.1Concrete Definition and Historical Development11.2Concrete as a Structural Material71.3Characteristics of Concrete101.4Types of Concrete141.5Factors Influencing Concrete Properties161.6Approaches to Study Concrete19Discussion Topics21References222Ma...

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    viiiContentsDiscussion Topics137Problems137References1384Structure of Concrete1404.1Introduction1404.2Structural Levels1414.3Structure of Concrete in Nanometer Scale: C–S–H Structure1454.4Transition Zone in Concrete1524.5Microstructural Engineering156Discussion Topics162References1635Hardened...

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    ContentsixDiscussion Topics374Problems375References3798Nondestructive Testing in Concrete Engineering3818.1Introduction3818.2Review of Wave Theory for a 1D Case3948.3Reflected and Transmitted Waves4038.4Attenuation and Scattering4068.5Main Commonly Used NDT-CE Techniques4078.6Noncontacting Resis...

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    PREFACEConcrete is the most widely used material in the world. It plays an important role in infrastructureand private buildings construction. Understanding the basic behaviors of concrete is essential forcivil engineering students to become civil engineering professionals. There have been some v...

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    xiiPrefaceIn the process of writing this book, the authors received enthusiastic help and invaluableassistance from many people, which is deeply appreciated. The authors would like to expresshis special thanks to Dr. Garrison C. K. Chau, Dr. Biwan Xu, and Dr. Jianzhong Shen for theirhelp in editi...

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    Advanced ConcreteTechnology

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    CHAPTER1INTRODUCTION TO CONCRETE1.1CONCRETE DEFINITION AND HISTORICAL DEVELOPMENTConcrete is a manmade building material that looks like stone. The word “concrete” is derivedfrom the Latin concretus, meaning “to grow together.” Concrete is a composite material com-posed of coarse granular...

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    2Chapter 1Introduction to Concreteand is then further reacted with CO2 to form limestone again:Ca(OH)2 + CO2+ H2Oambient temperature−−−−−−−−−−−−→ CaCO3+ 2H2O(1-4)The Egyptians used gypsum mortar in construction, and the gypsum was obtained by calciningimpure gypsum with ...

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    1.1Concrete Definition and Historical Development3Figure 1-2The Great Wall, built in the Qin dynastywas commissioned to rebuild the Eddystone Light house off the coast of Cornwall, England.Realizing the function of siliceous impurities in resisting water, Smeaton conducted extensiveexperiments w...

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    4Chapter 1Introduction to ConcreteBritannica, 1991). He decided, as a publicity stunt and to promote his cement business, to build ahouse made of b´eton arm´e, a type of reinforced concrete. In 1853, he built the first iron-reinforcedconcrete structure anywhere; a four-story house at 72 Rue Ch...

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    1.1Concrete Definition and Historical Development5Lane Memorial Bridge in Philadelphia, Pennsylvania, was completed in 1951. Nowadays, withthe development of prestressed concrete, long-span bridges, tall buildings, and ocean structureshave been constructed. The Barrios de Lura Bridge in Spain is...

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    6Chapter 1Introduction to ConcreteFigure 1-4Water Tower Place in Chicago, Illinois, USA (Photo provided by XiaojianGao)earthquake zone, concrete structures are usually heavily reinforced, especially at beam– columnjoints. Hence, due to low flowability, conventional concrete could hardly flow ...

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    1.2Concrete as a Structural Material7Figure 1-5The 225 West Whacker Drive building in Chicago, Illinois, USA (Photoprovided by Xiaojian Gao)with heating treatment. However, it is very brittle, hence, incorporating fibers into UHSC is nec-essary. After incorporating fine steel fibers, flexural...

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    8Chapter 1Introduction to Concretematerials other than aggregate (fine and coarse), water, and cement that are added into a concretebatch immediately before or during mixing. The use of admixtures is widespread mainly becausemany benefits can be achieved by their application. For instance, chem...

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    1.2Concrete as a Structural Material9Figure 1-6International Finance Center, Hong Kong (Photo courtesy of user WiNG onWikimedia Commons, http://commons.wikimedia.org/wiki/File:HK_ifc_Overview.jpg)Figure 1-7The Sutong Bridge in Suzhou, Jiangsu, China

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    10Chapter 1Introduction to ConcreteFigure 1-8Three Gorges Dam, Hubei, ChinaDams are other popular application fields for concrete. The first major concrete dams, theHoover Dam and the Grand Coulee Dam, were built in the 1930s and they are still standing.The largest dam ever built is the Three G...

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    1.3Characteristics of Concrete11Figure 1-9High-speed rail(b) Ambient temperature-hardened material : Because cement is a low-temperature bonded inor-ganic material and its reaction occurs at room temperature, concrete can gain its strengthat ambient temperature. No high temperature is needed.(c) ...

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    12Chapter 1Introduction to ConcreteFigure 1-10Baha’i TempleFigure 1-11Pipeline under construction (Photo courtesy of Exponent,http://www.exponent.com/corrosion_analysis_of_pre_stressed_concrete_pipeline/)

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    1.3Characteristics of Concrete13wood and steel. Even in a fire, a concrete structure can withstand heat for 2–6 hours,leaving sufficient time for people to be rescued. This is why concrete is frequently used tobuild up protective layers for a steel structure.(g) Ability to consume waste: With...

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    14Chapter 1Introduction to ConcreteSteelConcreteFigure 1-13Toughness of steel and concretecompression loads. Moreover, concrete can provide a structure with excellent stability.Reinforced concrete is realized as the second generation of concrete.(b) Low tensile strength: Concrete has different va...

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    1.4Types of Concrete15Figure 1-14Formwork for concrete castingTable 1-1Classification of concrete in accordance withunit weightClassificationUnit Weight (Kg/m3)Ultra-lightweight concrete<1200Lightweight concrete1200< UW< 1800Normal-weight concrete∼2400Heavyweight concrete>3200cons...

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    16Chapter 1Introduction to ConcreteTable 1-2Concrete classified in accordance with compressivestrengthClassificationCompressive Strength (MPa)Low-strength concrete<20Moderate-strength concrete20– 50High-strength concrete50– 150Ultra-high-strength concrete>150Table 1-3Concrete classi...

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    1.5Factors Influencing Concrete Properties17concrete compressive strength has been known since the early 1900s (Abrams, 1927), leadingto Abrams’s law:fc=AB 1.5(w /c)(1-7)where fc is the compressive strength, A is an empirical constant (usually 97 MPa or 14,000 psi),and B is a constant that dep...

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    18Chapter 1Introduction to Concreteparticle packing is based on the Apollonian concept, in which the smaller particles fit intothe interstices left by the large particles. Well-defined grading with an ideal size distributionof aggregate will decrease the voids in the concrete and hence the ceme...

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    1.6Approaches to Study Concrete191.5.6 CuringCuring is defined as the measures for taking care of fresh concrete right after casting. The mainprinciple of curing is to keep favorable moist conditions under a suitable temperature rangeduring the fast hydration process for concrete. It is a very i...

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    20Chapter 1Introduction to ConcretePerformanceProcessingMicrostructurePropertiesFigure 1-15Fundamental approach of materials research, 1Synthesis /ProcessingPerformancePropertiesStructure /CompositionEnd-use Needs / ConstraintsFigure 1-16Fundamental approach of materials research, 2a triangle for...

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    Discussion Topics21Synthesis /ProcessingPerformancePropertiesStructure /CompositionEnd-use Needs / ConstraintsMeasurementFigure 1-17Measurement is an essential part of materials science and engineeringBy adding measurement and characterization at the center of the base of the pyramid shownin Figu...

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    22Chapter 1Introduction to ConcreteHow would you like to improve concrete workability (fluidity or cohesiveness)?How can you enhance concrete compressive strength?Which principles are you going to follow if you are involved in a concrete research?REFERENCESAbrams, D. A. (1927) “Water– cement...

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    CHAPTER2MATERIALS FOR MAKING CONCRETEConcrete is one of the most versatile and widely produced construction materials in the world(Penttala, 1997). Its worldwide annual production exceeds 12 billion metric tons, i.e., more thantwo metric tons of concrete was produced each year for every person on...

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    24Chapter 2Materials for Making Concrete(a) In accordance with sizeCoarse aggregate: Aggregates predominately retained on a No. 4 (4.75-mm) sieve areclassified as coarse aggregate. Generally, the size of coarse aggregate ranges from 5 to150 mm. For normal concrete used for structural members suc...

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    2.1Aggregates25Figure 2-3Synthetic aggregates(b) In accordance with sourceNatural aggregates: This kind of aggregate such as sand and gravel is taken from naturaldeposits without changing the nature during production.Manufactured (synthetic) aggregates (see Figure 2-3): These kinds of aggregate a...

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    26Chapter 2Materials for Making Concreteand are most widely used. Concrete made with this type of aggregate has a bulk den-sity of 2300– 2400 kg/m3. It is the main concrete used to produce important structuralmembers.Heavy-weight aggregate: If the unit weight of aggregate is greater than 2100 k...

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    2.1Aggregates27(a) For the oven dry conditionMC(OD)=Wstock− WODWOD× 100%(2-1)where W stock is the weight of aggregate in the stock condition, and W OD the weight ofoven-dried aggregates. It can be seen that MCOD is a nonnegative value.(b) For the saturated surface dry conditionMC(SSD)=Wstock...

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    28Chapter 2Materials for Making Concreteon the definition of volume, the specific gravity can be divided into absolute specific gravity(ASG) and bulk specific gravity (BSG).ASG=weight of aggregateVsoliddensity of water=Dρw(2-6)andBSG=weight of aggregateVsolid+ Vporesdensity of water=BDρw(2-...

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    2.1Aggregates29where Wstock is the weight of the sample under the stockpile condition, and Wwater is the shortform of WSSD in water.If AC is known for the aggregate, MC(SSD) can also be calculated using the absorptioncapability of aggregates asMC(SSD)=Wstock− WOD(1+ AC)WOD(1+ AC)(2-13)2.1.4 Gra...

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    30Chapter 2Materials for Making Concrete020406080100Cumulative mass percent finer1010.10.010.001Grain diameter, mmOpenWell-gradedUniformGap-gradedDenseFigure 2-5Five types of aggregate gradationIt can be seen from the formula that calculation of the fineness modulus requires that the sumof the c...

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    2.2Cementitious Binders31SphericalCubicalIrregularIrregularFlatFlatNeedle-ShapedPrismaticFigure 2-6Different basic shapes of aggregatesTable 2-2Effects of aggregate shape and surfacetexture on concrete strengthRelative Effect (%) ofAffected StrengthShapeSurface TextureCompressive2244Flexural31262...

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    32Chapter 2Materials for Making Concretecommonly used organic binders. Polymers consist of random chains of hydrocarbons and canbe classified into thermoplastics, thermosets, and elastomers (or rubbers). Carbon atoms formthe skeleton of the polymer chain. Along each chain, there are typically 10...

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    2.2Cementitious Binders33Asphalt cement is mainly obtained from the distillation of crude oil. With very high molec-ular weight, asphalt is generally hard and relatively solid in its original form. Thus, it is easilydistributed. To use it in practice, asphalt needs to be softened by heating. To r...

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    34Chapter 2Materials for Making Concretematerials could increase the water-resistance properties. He was the first person to control theformation of hydraulic lime. He used a mortar prepared from a hydraulic lime mixed withpozzolan from Italy to build the Lighthouse, which was to last 126 years....

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    2.2Cementitious Binders35Figure 2-8A production line of 10,000 metric tons per day (Hai Luo Cement Company,China)FromquarriesCrusherHammer MillBall MillBall MillTo marketsCementstorage silosFeedstorage silosBlendingsilosHeat exchangersRotary kilnCoolerGypsumClinkerstorageRaw materialstorageFigure...

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    36Chapter 2Materials for Making Concrete(b) Limestone (CaCO3) is mainly providing calcium (CaO) and is decomposed at 1000◦C:CaCO3(1000◦C)−−−−−−→ CaO+ CO2(2-20)(c) Iron ore and bauxite provide additional aluminum and iron oxide (Fe2O3), which help theformation of calcium silicate...

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    2.2Cementitious Binders37Table 2-4Major compounds of ordinary Portland cementCompoundOxide CompositionColorCommon NameWeight PercentageTricalcium silicateC3SWhiteAlite50Dicalcium silicateC2SWhiteBelite25Tricalcium aluminateC3Awhite/greyn/a12Tetracalcium aluminoferriteC4AFBlackFerrite8(b) Major co...

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    38Chapter 2Materials for Making Concrete(c) Minor components of Portland cement : The most important minor components of cementare gypsum, MgO, and alkali sulfates. Gypsum (2CaSO4· 2H2O) is added in the last pro-cedure of grinding the clinker to produce Portland cement. The reason for adding gyp...

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    2.2Cementitious Binders39leaching due to its solubility, carbonation due its reaction with carbon dioxide, alkali aggregatereaction due to its high pH value, or sulfate attack due to its reaction with sulfate. Hence, incontemporary concrete technology, there has been a trend to reduce amount of C...

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    40Chapter 2Materials for Making ConcreteThe reaction occurs so fast that it causes flash set of concrete. The hydration products of C4AFare similar to those of C3A. However, the reaction rate of C4AF is slower than that of C3A.When reacting with gypsum, the following equation applies:C4AF+ 3 CSH...

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    2.2Cementitious Binders418,0006,0004,0002,000020406080100C3SC3A + CSH2C4AF + CSH2C2STime (days)Compressive strength (lb/in2 )Compressive strength (MPa)06040200Figure 2-12Strength development of primary constituents of Portland cementTime (hours)Stage 5Stage 3 & 4C3A hydrationC3S hydrationRate...

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    42Chapter 2Materials for Making ConcreteTable 2-6Kinetics of reaction, chemical processes, and relevance to concrete of the different reactionstages of cementReaction StageKinetics of ReactionChemical ProcessesRelevance to Concrete1. Initial hydrolysisChemical control; rapidInitial hydrolysis;dis...

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    2.2Cementitious Binders43Hardened pasteFresh pasteC3SC3SInitial setFinal setFigure 2-14Setting of fresh cement pasteThe cement hydration process was traditionally studied using the calorimetric method. Thehydration stages were identified by heat liberation measurement and the hydration mechanism...

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    44Chapter 2Materials for Making ConcreteTransformerCurrent meterVI(Primary coil)Sample cast in the mold(Second coil)Figure 2-15Electrical resistivity measurement setup224602MLLMMLMixinghydration timeElectrical resistivity responseSetting time(ASTM C191)P1P1P2P2tLtm0tp1tp2tLtmtp1tp2initialtinifina...

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    2.2Cementitious Binders45the curve of dρ(t )/dt− t . The times at which the characteristic points occurred and the pastesetting time are listed in the table in Figure 2-16. According to the characteristic points, thehydration process is divided into five stages: dissolution, dynamic balance, ...

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    46Chapter 2Materials for Making ConcreteGypsum:small lathlike crystalsAFt:hexagonal short rodsAFt not evenly distributedon cement grain surfaceAFt hexagonal short rodsC-S-H: fibrillar(a) t = 0, anhydrous cement102-Theta, CuKα152025CHAFT0.73h102-Theta, CuKα152025CHAFT3h(b) t = 0.73h (at point M)...

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    2.2Cementitious Binders47C4AH19 & C-S-HHydrates networking(e) t = 12.8h (at point P2), AFt transfers to AFm(f) t = 24h102-Theta, CuKα152025CHAFm12.8hCHAFtAFtAFm24h102-Theta, CuKα152025Figure 2-17(continued)AFm formedgypsum consumedpeak 1 peak 2 peak 3peak 4∆H = 9.55 J/g∆H = 11.94 J/g∆...

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    48Chapter 2Materials for Making Concrete9245235185185185185189229259269740.73hanhhdrouscement3422342234223402342236434000 3800 3600 3400 3200300000.10.20.300.10.20.30.40.50.632003400A - 6.7hB - 12.8h360030003200340036003000 2800 2600 2400 2200wavenumber (cm−1)peaks centered at 3422 cm−1peaks ...

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    2.2Cementitious Binders49At same time, a supersaturation point of Ca2+ is reached, and the CH precipitates fromthe solution, as detected by DTA technique in the hydrated sample for 0.73 h, which is shownin Figure 2-18. The DTA results show that the index of CH (peak 4) content in the hydratedsamp...

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    50Chapter 2Materials for Making Concreteduring the period of 6.7–12.8 h. When there is sufficient SO42− in the pore solution, the ettringiteforms and remains stable. After SO42− is consumed, the ettringite is transformed into mono-sulfate (AFm). The DTA results at 6.7 and 12.8 h, as shown ...

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    2.2Cementitious Binders51Table 2-7New understanding of the stages of hydration processHydration StageKinetics ofHydrationMain ChemicalPhenomenaChemical ReactionI. Dissolution(mixing to M )Ion dissolutiondominatingInitial rapid chemicalreaction of C3AC3A+ 3 CSH2+ 26H→ C6AS3H32II. Dynamicbalance(...

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    52Chapter 2Materials for Making ConcreteType IIIType IIType IType IV3020Time (days)Adiabatic temperature rise in mass concrete (°C)10030405020100Figure 2-20Adiabatic temperature rise in mass concretes with different types ofcement714IVII, VIIIIType II, IV, VIIII2890180Time (days)Compressive stre...

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    2.2Cementitious Binders53Table 2-8Chemical compositions and physical properties of different Portland cementsPortland Cement TypeChemical Compositions and Physical PropertiesIIIIIIIVVC3S5045602540C2S2530155040C3A1271054C4AF81281210CSH255544Fineness (Blaine, m2/kg)350350450300350Compressive streng...

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    54Chapter 2Materials for Making Concretewhere w is the original weight of water, c is the weight of cement, and w /c is the water tocement ratio. It can be seen that with an increase of w /c, the capillary pores increase. Thegel/space ratio (X ) is defined asX=volume of gel (including gel pores)...

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    2.2Cementitious Binders55Figure 2-22BET surface area analyzerwhere V is the velocity of the cement particle falling in the viscous medium (kerosene),η isthe viscosity coefficient, g is the acceleration of gravity, D 1 is the density of the particles, andD 2 is the viscous medium. A similar inst...

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    56Chapter 2Materials for Making ConcreteFigure 2-23Particle size analyzerside about 150 times per minute against the palm of the other hand on the upstroke. Performthe sieving over a sheet of white paper. Return any material escaping from the sieve or pan andcollecting on the paper. The fineness...

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    2.2Cementitious Binders57(c) Time of setting: This test is undertaken to determine the time required for the cementpaste to harden. The initial set cannot be too early due to the requirements of mixing, conveying,placing, and casting. Final setting cannot be too late owing to the requirement of s...

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    58Chapter 2Materials for Making Concrete30 mm30 mm165 mmIndicator pointsFigure 2-24Le Chatelier test apparatuscalled the heat of solution method. Basically, the heat of solution of dry cement is compared tothe heats of solution of separate portions of the cement that have been partially hydrated ...

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    2.2Cementitious Binders59Energy saving and environment protection: Geopolymers do not require large energy con-sumption. A great amount of CO2 is emitted during the production of Portland cement, which isone of the main reasons for global warming. Studies have shown that one ton of carbon dioxide...

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    60Chapter 2Materials for Making Concreteet al., 1997), thermal stability, and high acid resistance. Any current building component,such as bricks, ceramic tiles, and cement, could be replaced by geopolymers.(c) Automotive and aerospace: The merits of high-temperature resistance allow geopolymerst...

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    2.2Cementitious Binders61(c) Archeological research: In the 1970s, Davidovits proposed a controversial theory docu-mented in a book by Lyon, (1994) and has since gained widespread support and acceptance.He postulated that the great pyramids of Egypt were not built by natural stones, but thatthe b...

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    62Chapter 2Materials for Making ConcreteTable 2-9Reaction heats of single 6-member ring structure models under strongly alkaline solution(a)Single6-memberringofSiO4 tetrahedralReaction Enthalpy (kJ/mol)Molecular Structural UnitFormation Enthalpy∆E1∆E2∆E3∆E4(Si(OH)2O)6−1491.45(OH)3Si–(...

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    2.2Cementitious Binders63Al−(OH)2O)6+ 3KOH→(OH)3Al−− (Al−(OH)2O)3− Al−(OH)3+ HO− Al−≡(OK)3 + H2OE6(2-44)Al−(OH)2O)6+ 4NaOH→(OH)3Al−–(Al−(OH)2O)3–Al−(OH)2–ONa+ HO–Al−≡(ONa)3 + 2H2OE7 (2-45)(Al−(OH)2O)6+ 4KOH→(OH)3Al−–(Al−(OH)2O)3–Al−(OH)2–O...

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    64Chapter 2Materials for Making ConcreteAlAlAlAlAlAlAlAlAlAlAlSiSiSiSiSiSiSiSiSiSiSiSiAlAlAlAlAlSiSiSiSiOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOAlAlAlAlAlAlAlAlAlAlAlAlAlAlAlAlAlAlAlAlAlAlAlAlAlAlAlAlAlSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiSiOOOOO...

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    2.2Cementitious Binders65even tails in gold mines can also be utilized in MPC in large amounts. These wastes aredifficult to use in PC concrete in appreciable amounts.(c) Due to the high alkali environment of PC (pH over 12.5), when they are used with fiberreinforcement, some components such as...

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    66Chapter 2Materials for Making Concretewaste can be recycled to useful building materials, and (2) many toxic and radioactive wastesare difficult to treat with traditional processes, but can be easily treated by MPC. This functionensures more promising uses of MPC in the future, especially for ...

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    2.2Cementitious Binders67wastes, no single solidification technology can be used to successfully treat and dispose of them.For example, the low-level wastes contain both hazardous chemical and low-level radioactivespecies (Singh et al., 1997). To stabilize them requires that the two kinds of con...

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    68Chapter 2Materials for Making Concreteternary MOC system are 2Mg(OH)2•MgCl2•4H2O (phase 2), 3Mg(OH)2•MgCl2•8H2O (phase 3),5Mg(OH)2•MgCl2•8H2O (phase 5), and 9Mg(OH)2•MgCl2•5H2O (phase 9). Of these, phases 3and 5 may exist at ambient temperature, whereas phases 2 and 9 are stable...

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    2.3Admixtures69Table 2-10Beneficial effects of different kinds of admixtures on concrete propertiesConcrete PropertyAdmixture TypeCategory of AdmixtureWorkabilityWater reducersChemicalAir-entraining agentsAir entrainingInert mineral powderMineralPozzolansMineralPolymer latexesMiscellaneousSet co...

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    70Chapter 2Materials for Making Concrete(a)(b)(c)(d)Figure 2-27Commonly used admixtures: (a) corrosion inhibitor; (b) set-retardingadmixture; (c) air entraining agent; and (d) high-range water-reducing admixture (super-plasticizer).durability of concrete. However, water reducers may also be emplo...

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    2.3Admixtures71Figure 2-28Structure of PCEBeforeAfter using the admixtureFigure 2-29Mechanism of water-reducing admixtureFigure 2-28. For these molecules to be effective as dispersants, they must be attracted to thesurface of a cement particle. The backbone of the polycarboxylate molecules typica...

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    72Chapter 2Materials for Making ConcreteSolubleChainsFigure 2-30Steric effect of PCEis 4.5/0.3= 15 kg. Thus, the additional water added into concrete mix is 10.5 kg, that has to bededucted from the free mixing water.Superplasticizers (SPs) are used mainly for two main purposes: (1) to produce hig...

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    2.3Admixtures73admixture increases with the molecular weight of the polymer, and the presence of calciumions promotes this adsorption. In the case of the lignosulfonates (Rixom and Mailvaganam,1999), the presence of low-molecular-weight ingredients causes excessive air entrainment andleads to los...

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    74Chapter 2Materials for Making Concrete00.4Kt,KrKtKr32.521.510.500.20.6Dosage of superplasticizer (%)0.811.21.4Figure 2-32Typical plot of Kt and Krof the reference paste without SP addition. In this method, two parameters are proposed forselecting SPs:Kt=ti, SPti, P 0(2-47)where ti, SP is the in...

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    2.3Admixtures75improvement in restrained shrinkage performance. Even for concrete with proper curing at whichthe drying shrinkage would reduce to minimum, there is still a substantial reduction in dryingshrinkage due to effect of SRA (Berke, et al., 1999). The main mechanism of SRA in reducingdry...

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    76Chapter 2Materials for Making ConcreteAdmixture concentrationRetardingAcceleratingIIIIIIIVVTime of initial setFigure 2-33Different types of setting-control admixtureswhen it has a problem in traffic or operation. Figure 2-33 demonstrates the different types ofsetting control admixtures: monoto...

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    2.3Admixtures77Air bubbleHydrophilicHydrophobicFigure 2-34Mechanism of air entrainingInterparticlespacingbetweenC-S-H sheetsCapillary voidsAggregation ofC-S-H particlesHexagona crystals ofCa(OH)2 or low sulfate in cement pasteEntrainedair bubblesMax. spacingof entrained airfor durabilityto frost ...

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    78Chapter 2Materials for Making Concrete0020406080100Durability factor (%)Spacing factor (mm)0.10.20.30.40.50.6Figure 2-36Effects of spacing factor on durability factor00510152001,0002,0003,0004,0005,000510Air content (% by volume)Compressive strength (b/in2 )DurabilityCompressive strengthDurabil...

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    2.3Admixtures79This is because more paste is required to provide similar workability for concrete with a smallersize of coarse aggregate due to the surface coating requirement.The formula used to calculate the gel space ratio has to be modified if entrained air incement paste is considered:X=vol...

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    80Chapter 2Materials for Making Concrete100020406080100101Equivalent spherical diameter, mASTM Type IPortland CementTypicalHigh-CalciumFly AshTypicalLow-CalciumFly AshCondensedSilica FumeCumulative mass, % finer0.10.01Figure 2-39Size distribution of typical Portland cement, fly ash, and silica f...

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    2.3Admixtures81of Portland cement, it can easily fill in the space between cement particles. Subsequently, adenser concrete microstructure can be achieved and a high compressive strength can be reached.Pozzolanic reaction is defined aspozzolan+ calcium hydroxide+ water= calcium silicate hydrate...

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    82Chapter 2Materials for Making ConcreteTable 2-12Chemical composition of MK (%)SiO2Al2O3Fe2O3CaOLOI51.3441.950.520.340.72water-reducing admixture than that modified by SF to achieve a comparable fluidity (Caldaroneet al., 1994). It has also been demonstrated that MK is particularly effective i...

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    2.3Admixtures83(a) Fly ash(b) Silica fumeFigure 2-41Morphology of fly ash and silica fumeFigure 2-42Fly ash particle having plerospheresfly ash. Usually, high-calcium fly ash is more reactive because it contains most of the calciumin the form of reactive crystalline compounds, such as C3A and ...

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    84Chapter 2Materials for Making Concreteby product, it lowers the energy demand in producing concrete. In addition, incorporating flyash into concrete can reduce the hydration heat of fresh concrete and is good for mass concretestructures.The disadvantages of fly ash concrete are low early age ...

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    2.4Water85Table 2-14Chemical composition of slag (%)CaOSiO2Al2O3Fe2O3MgOSO3K2ONa2OLOI30– 45∼3010– 151– 2<6<60.4– 1.50.05– 0.50.2– 1100 years. The typical chemical composition of slag is shown in Table 2-14. It can be seen fromthe table that CaO and SiO2 are the two main compon...

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    86Chapter 2Materials for Making ConcreteTable 2-15Benefits of using mineral admixtures in fresh concreteWorkability of Fresh ConcreteMineralUsualEconomicProtectingIncreasingIncreasingDecreasingAdmixturesDosagea (%)BenefitsEnvironmentFluidityCohesivenessSegregationPFA or FA10– 40BFS or slag20...

  • Page 102

    2.4Water87quantities of organic matter into streams, lakes, and reservoirs. As a result, the degree of organiccontamination in surface waters reaches a peak in spring, and falls to a minimum in summer.Excessive impurities in mixing water not only may affect setting time and concrete strength,but ...

  • Page 103

    88Chapter 2Materials for Making Concretecategory, as well as phosphates, arsenates, and borates. Soluble inorganic salts of up to 500 ppmcan generally be tolerated in mixing water. Acidic waters can be used in concrete making; thepH of the water may be as low as 3.0, at which level there are more...

  • Page 104

    Problems89Why can the moisture content influence concrete properties?What are the differences between organic and inorganic binders?What are the differences between hydraulic and nonhydraulic cement?What are main chemical components of Portland cement?What are main hydration products of Portland...

  • Page 105

    90Chapter 2Materials for Making Concrete6. The material ratio for concrete mix is 1:1.5:2 (C:Sand:Coarse Aggregate by weight). The BSG for cementis 3.15, for sand is 2.5 and for coarse aggregate is 2.7. Air content is 4.8%. The gel/space ratio is 0.72.Calculate the water cement ratio forα=0.8?7....

  • Page 106

    References91Deng, D. (2003) “The mechanism for soluble phosphates to improve the water resistance of magnesiumoxychloride cement,” Cement and Concrete Research, 33, 1311– 1317.Deng, D. and Zhang, C. (1999) “The formation mechanism of the hydrate phases in magnesium oxychloridecement,” C...

  • Page 107

    92Chapter 2Materials for Making ConcreteLyon, R. E., Foden, A., Balaguru, P. N., Davidovits, M., and Davidovits, J. (1997) “Fire resistant alumino-silicate composites,” Journal Fire and Materials, 21(1), 67– 73.Maravelaki-Kalaitzaki, P. and Moraitou, G. (1999) “Sorel’s cement mortars de...

  • Page 108

    References93Uchikawa, H., Hanehara, S., and Sawaki, D. (1997) “The role of steric repulsive force in the dispersion ofcement particles in fresh paste prepared with organic admixture,” Cement and Concrete Research, 27,37– 50.Urwongse, L. and Sorrell, C. A. (1980) “The system MgO–MgCl2–...

  • Page 109

    CHAPTER3FRESH CONCRETEFresh concrete is defined as a fully mixed concrete in a rheological state that has not lost itsplasticity. The fresh concrete stage covers the cement hydration stages I and II. The plastic stateof fresh concrete provides a time period for transportation, placing, compactio...

  • Page 110

    3.1Workability of Fresh Concrete95paste and the internal friction between the aggregate particles, on the one hand, and the externalfriction between the concrete and the surface of framework, on the other hand. Workability offresh concrete consists of two aspects: consistency and cohesiveness. Co...

  • Page 111

    96Chapter 3Fresh Concrete300±3mm100±3mm200±3mm(12±18in.)(8±18in.)(4±18in.)Foot piecesLifting handlesFigure 3-1Truncated cone for the slump testabcFigure 3-2Sequence of slump testIf slumping occurs evenly all around, it is regarded as a true slump. If one-half of the coneslides down along an...

  • Page 112

    3.1Workability of Fresh Concrete97240mm200mmLooseguideMetal shaftTransparent diskStandard slump coneVibratingtableTotal weight = 2750±50gFigure 3-3Vebe test setup3.1.2.2 Vebe testThe test equipment, which was developed by Swedish engineer V. Bahrner, is shown inFigure 3-3. It consists of a vibra...

  • Page 113

    98Chapter 3Fresh Concrete260mm130mm280mmHinged door260mm130mm280mm150mm285mm200mm200mmHinged doorFigure 3-4Compaction factor test apparatusThe weight of the cylinder is measured as Mf, representing the fully compacted cylinder mass.The compaction factor is defined ascompaction factor=MpMf(3-1)Us...

  • Page 114

    3.1Workability of Fresh Concrete993.1.2.4 Ball penetration testASTM C360 covers the Kelly ball penetration test. The test setup is shown in Figure 3-5. A152-mm-diameter hemisphere hammer of weight 13.6 kg is connected to a handle with a ruler.The hammer is fixed on a box container through a pin....

  • Page 115

    100Chapter 3Fresh Concretemeasurement is close to the definition of workability given by Mindess et al. (2003). Thepenetration test is usually very quick and can be done on site, right in the formwork, providedit is wide enough. The ratio of slump value to penetration depth is from 1.3 to 2.0.3....

  • Page 116

    3.1Workability of Fresh Concrete101angular sands will require more paste for a given consistency; alternatively, they will produceharsh and unworkable mixtures at water contents that might have been adequate with coarser orwell-rounded particles. In general, to get a similar consistency of concre...

  • Page 117

    102Chapter 3Fresh Concrete3.1.4 Segregation and bleeding3.1.4.1 SegregationIn discussing the workability of concrete, it has been pointed out that cohesiveness is an importantcharacteristic of the workability. A proper cohesiveness can ensure concrete to hold all theingredients in a homogeneous w...

  • Page 118

    3.1Workability of Fresh Concrete103the mix tends to rise to the surface of freshly placed concrete. This is caused by the inability ofthe solid constituents of the mix to hold all the mixing water when they settle downward dueto the lighter density of water. Bleeding can be expressed quantitative...

  • Page 119

    104Chapter 3Fresh ConcreteFigure 3-8Measurement setup of concrete mixture setting time3.1.6.2 Abnormal setting(a) False setting: If a concrete stiffens rapidly in a short time right after water is addedand restores its fluidity by remixing and sets normally, it is called false setting. The main ...

  • Page 120

    3.1Workability of Fresh Concrete105false setting. However, as mentioned before, flash setting has been largely eliminated by theaddition of 3 to 5% gypsum to the cement, which can react with C3A and water to formAFt as a barrier layer of C3A to prevent further reaction of C3A, as discussed in Ch...

  • Page 121

    106Chapter 3Fresh ConcreteTime (log scale) (min)Time (min)ti = 1.8807tm+0.4429tttf = 0.9202tt+0.2129PmElectrical resistivity (ohm.m)501015102025100tiDissolvingPmtmElectrical resistivity (ohm.m)02.02.53.03.54.0100Pt1000tttfMix 10Mix 3Mix 110000Determined by Fig (b)200Setting300PtHardening400Mix 3M...

  • Page 122

    3.2Mix Design1073.2 MIX DESIGNThe mix design of concrete is the process of deciding what type of raw material and howmuch of each raw material needs to be selected to make concrete that can meet prerequisitessuch as strength, durability, and workability. The required properties of hardened concre...

  • Page 123

    108Chapter 3Fresh ConcreteAs mentioned earlier, under normal conditions, it is sufficient to consider workability andstrength for concrete design. For special conditions, additional considerations on dimensionalstability and durability have to be taken into account.3.2.2 Weight method and absolu...

  • Page 124

    3.2Mix Design109Table 3-1Relation between w/c and average compressive strength of concrete, according to ACI211.1-81Average CompressiveEffective Water/Cement Ratio (by Mass)Strength at 28 Daysa (MPa)Non-Air-Entrained ConcreteAir-Entrained Concrete450.38—400.43—350.480.40300.550.48250.620.5320...

  • Page 125

    110Chapter 3Fresh Concretemethod, the mass of the cementitious material is smaller than that of the cement in the Portland-cement-only mix so that the water/cementitious material ratio is greater than in the Portland-cement-only mix. Whichever approach is used, a partial replacement of cement by ...

  • Page 126

    3.2Mix Design111Table 3-4Requirements of ACI 318-83 for minimum cover for protection of reinforcementMinimum Cover in mmReinforced ConcretePrecastPrestressedExposure ConditionCast in SuitConcreteConcreteConcrete cast against, or permeabilityexposed to, earth70—70Concrete exposed to earth or wea...

  • Page 127

    112Chapter 3Fresh ConcreteTable 3-6Workability, slump, and compacting factor of concretes with 19 or 38 mm maximum sizeof aggregateDegree ofSlumpCompactingWorkability(mm)(in.)FactorUse for which Concrete is SuitableVery low0– 250– 10.78Roads vibrated by power-operated machines.At the more wor...

  • Page 128

    3.2Mix Design113Table 3-8Approximate requirement for mixing water and air content for different workabilitiesand nominal maximum sizes of aggregates according to ACI 211.1-81Workability orWater Content (kg/m3) of Concrete for Indicated MaximumAir ContentAggregate Size in mm1012.52025405070150Non-...

  • Page 129

    114Chapter 3Fresh Concrete3.2.3.5 Major aggregate properties and aggregate contentMany parameters have to be determined in choosing an aggregate. Usually, the maximum size ofaggregate is determined first, as it has a significant influence on concrete properties. In reinforcedconcrete, the maxi...

  • Page 130

    3.2Mix Design115Table 3-10Example of grading of individual coarse aggregate fractions to be combined into an ‘‘ideal’’grading for mass concreteCumulative Percentage Passing for Fraction (%)Sieve Size (mm)150– 75 mm75– 37.5 mm37.5–19 mm19– 4.76 mm175100———15098———100301...

  • Page 131

    116Chapter 3Fresh ConcreteTable 3-12First estimate of density (unit weight) of fresh concrete as given by ACI 211.1-81Maximum Size ofFirst Estimate of Density (Unit Weight) of Fresh Concrete kg/m3Aggregate (mm)Non-Air EntrainedAir Entrained102285219012.52315223520235522802523752315402420235550244...

  • Page 132

    3.3Procedures for Concrete Mix Design117(c) Bulk specific gravity of each raw material(d) Absorption capacity or moisture content of the aggregates(e) Variation of the approximate mixing water requirement with slump, air content, and gradingof the available aggregates(f) Relationships between st...

  • Page 133

    118Chapter 3Fresh Concretea unit volume of concrete depends only on its maximum size and fineness modulus ofthe fine aggregate. It is assumed that differences in the amount of mortar required forworkability with different aggregates, due to differences in particle shape and grading,are compensa...

  • Page 134

    3.3Procedures for Concrete Mix Design119(b) If the desired air content is not achieved, the dosage of the air-entraining admixtureshould be adjusted to produce the specified air content. The water content is thenincreased (or decreased) by 3 kg/m3 for each 1% decrease (or increase) in aircontent...

  • Page 135

    120Chapter 3Fresh Concreteconcrete. And, the OD weight of the coarse aggregate is 0.64× 1600= 1.024 kg. TheSSD weight is 1024× 1.005= 1029 kg.Step 7: Estimation of fine aggregate content. The fine aggregate content can estimated by eitherthe weight method or the volume method.(a) Weight metho...

  • Page 136

    3.3Procedures for Concrete Mix Design121Step 9: Trial mixes. Trial mixes should be carried out using the proportions calculated. Theproperties of the concrete in the trial mix must be compared with the desired properties,and the mix design must be corrected as described.Example II Raw material ca...

  • Page 137

    122Chapter 3Fresh Concrete6. For retarderWsolid= 0.0025× 23.48= 0.059 kgWsolution= 0.059/0.035= 0.168 kgWater provided by retarder solution= 0.168− 0.059= 0.109 kg7. For superplasticizerWsolid= 0.015× 23.48= 0.352 kgWsolution= 0.352/0.4= 0.881 kgWater provided by superplasticizer solution= 0....

  • Page 138

    3.5Delivery of Concrete123Figure 3-11Ready-mix concrete plantFigure 3-12Small pan mixer3.5 DELIVERY OF CONCRETEThe delivery of fresh concrete from the concrete plant to the construction site is usually doneby agitators, either truck mixers or truck agitators. The truck is equipped with a rotating...

  • Page 139

    124Chapter 3Fresh ConcreteFigure 3-13Delivery of concrete by truckFigure 3-14Delivery of concrete to an ocean construction site using a ferry (photo providedby Ove Arup, HK)advantage of truck mixing is that the water can be stored separately and added into the solidmaterials for mixing according ...

  • Page 140

    3.6Concrete Placing125initial setting time of 7 to 8 h. In this case, A truck mixer has priority to be selected, if available.A truck mixer has to meet the requirements of environmentally friendly production nowadays.3.6 CONCRETE PLACINGPlacing concrete is a construction process that can be divid...

  • Page 141

    126Chapter 3Fresh ConcreteFigure 3-15Framework for transfer block of a tall building (photo provided by Peter Allen)concrete and some construction load until the concrete hardens and can carry the load itself.The formwork can be built with steel plate or timber board. Formworks should be clean, t...

  • Page 142

    3.6Concrete Placing127(d) Reinforcing steel : After the formwork is built up, a reinforcing steel cage has to be putinto the formwork before concrete casting. The main reinforcing steel bars should be held bysteel stirrups in the right position. The reinforcing steel should be free of dirt, paint...

  • Page 143

    Figure3-16Reinforcingsteelframework(photoprovidedbyMr.PeterAllen)128

  • Page 144

    3.6Concrete Placing129Figure 3-17Concrete is conveyed into a large foundation construction through chutes(photo provided by Mr. Allen)Figure 3-18Unloading concrete (photo provided by Ove Arup, HK)

  • Page 145

    130Chapter 3Fresh ConcreteFigure 3-19Wheelbarrow used on construction site0.12 or 0.2 m3 each, with a maximum haul of about 60 m. A power-driven cart has a capacityof up to 1.2 m3 and can move a maximum of 17 m3 of concrete per hour on a moderate lengthof haul. Maximum haul should not exceed 300 ...

  • Page 146

    3.6Concrete Placing131Figure 3-20Pumping of fiber-reinforced concrete to a height of 306 m at Su-TongBridge, Suzhou, China (photo provided by Jinyang Jiang)Figure 3-21Drop chute-guided concrete fallvertically. In most cases, free fall should be limited to 0.9 to 1.5 m to avoid aggregate bouncing...

  • Page 147

    132Chapter 3Fresh ConcreteFor concrete deposited in the formwork of walls, footings, beams, and shear walls, concreteshould be placed from the ends or corners toward the center, in horizontal layers not exceedingabout 450 mm in depth. Mass concrete in dams and foundations is usually placed in lif...

  • Page 148

    3.6Concrete Placing133Figure 3-22Internal vibrationOvervibration sometimes occurs. If so, the coarse aggregate will have sunk below thesurface, and the surface may have a frothy appearance. In this case, the slump should first bereduced, and the amount of vibration then has to be adjusted.A simp...

  • Page 149

    134Chapter 3Fresh ConcreteFigure 3-23Decoration effect of concretetemperature. In the fabrication of precast concrete components, steam curing is often employed,and the 7-day strength under normal curing can be achieved in 1 day. The mold can thenbe reused, leading to a more rapid turnover. If cu...

  • Page 150

    3.7Early-Age Properties of Concrete135Figure 3-24Plastic shrinkage crack3.7 EARLY-AGE PROPERTIES OF CONCRETEFor concrete at an age less than 7 days, cement paste in the concrete undergoes a fast hydrationprocess. Thus, both the mechanical properties and the pore size distribution of the concrete ...

  • Page 151

    136Chapter 3Fresh Concrete0.0000.0010.00228 day7 day3 day2 day18 hours1 day0.0030.0040.005Strain (mm/mm)50403020Stress (MPa)1000.0060.0070.0080.009Figure 3-25Complete stress–strain curves of NSC0.001 0.002 0.00328 days7 days3 days2 days18 hours1 day0.004 0.005 0.006Strain (mm/mm)100806040Stress...

  • Page 152

    Problems137Table 3-13E modulus of concreteAge18 H1 Day2 Days3 Days7 Days28 DaysNSC12.9514.9216.1215.9624.0425.47HSC10.5318.8822.3928.2430.0233.05for concrete at early age, compared to a mature concrete’s brittleness, due to its viscous char-acteristics. From the test results for compressive str...

  • Page 153

    138Chapter 3Fresh Concretestandard with a fineness modulus of 2.8. (Assume that absorption is 0.7% and moisture condition ofthe aggregates is SSD; the bulk density of coarse aggregate is 1600 kg/m3; and there will be extremeexposure condition to freeze-thawing.)2. Use the American method to desi...

  • Page 154

    References139Mindess, S.,Toung, J. F., and Darwin, D. (2003) Concrete, 2nd ed., Upper Saddle River, NJ; USA,Pearson Education.Neville, A. M. and Brooks, J. J. (1994) Concrete Technology, Longman.Pessiki, S. P., and Carino, N. J. (1988) “Setting time and strength of concrete using the impact-ech...

  • Page 155

    CHAPTER4STRUCTURE OF CONCRETE4.1INTRODUCTIONThe type, amount, size, shape, and distribution of different phases present in concrete constituteits structure. The structure is multiscale in nature, ranging from nanometer scale, to micrometerscale, to millimeter scale. The elements of the structure ...

  • Page 156

    4.2Structural Levels141concrete, to develop an appreciation of the structure of ordinary Portland cement concrete, andto outline an approach to microstructural engineering—methods of modifying the structure.4.2STRUCTURAL LEVELSConcrete is a typical multiscale material. Its structure cannot be a...

  • Page 157

    142Chapter 4Structure of ConcreteFigure 4-1Visual level of a concrete’s structure (mm scale)Figure 4-2Structure of concrete at petrographic level (the white spots are unhydratedcement particles; the black ones are air voids)

  • Page 158

    4.2Structural Levels143Figure 4-3Structure of concrete at the intermediate SEM levelmagnification of 200×. From the figure, the lower grade of fine aggregates, such as finer sandof size of the order of tens of micrometers, entrapped air voids, and unhydrated cement particlescan be observed.T...

  • Page 159

    144Chapter 4Structure of Concreteand the needle-shaped AFt can be clearly distinguished. In this level, the structure of individualcement particles, the details of different hydration products, and the lower grade of the capillarypores can be observed. From Figure 4-4, it can be seen that the str...

  • Page 160

    4.3Structure of Concrete in Nanometer Scale: C–S–H Structure145Figure 4-6Reacted fly ash particle in concreteshows an SEM photo of the secondary mode taken at a magnification of 20,000×.The mor-phology of C–S–H can be clearly observed. Figure 4-6 shows a fly ash particle in cement pas...

  • Page 161

    146Chapter 4Structure of Concrete45.65[nm]0.000.000.100.200.000.100.00250.00× 250.00 [nm] Z 0.00 - 45.65 [nm]250 nm × 250 nm (C90d)250.00× 250.00 [nm]100.00 [nm]0.2045.65[nm]Figure 4-7AFM photo of C–S–H at nanometer scaleapproximately 50– 70% of the fully hydrated cement paste and makes ...

  • Page 162

    4.3Structure of Concrete in Nanometer Scale: C–S–H Structure147Q2Q2pQ2iQ2vQ3Q1Figure 4-8Different types of silicate formationIn 29Si MAS-NMR, Q 1 and Q 2 predominate. The ratio of Q 1/Q 2 declines with the hydrationprogress, indicating that the lengths of silica chains are prolonged at the ex...

  • Page 163

    148Chapter 4Structure of ConcreteFigure 4-9TEM of inner product and outer product of C–S–H4.3.2 Common C–S–H modelsWith more than half a century’s development, a large number of C–S–H gel models havebeen proposed to describe the relative nanostructure. Richardson has systematically ...

  • Page 164

    4.3Structure of Concrete in Nanometer Scale: C–S–H Structure149BPP14.00 AacbBBPPBFigure 4-10The structure of 14 ˚A tobermorite (Bonaccorsi et al., 2005) B-bridginglayer P-paired layerSiSiOOOOOOOOOOHOCaOOOCaOSiSiOCaOOCaOSiSiHO8H2OO(−)Ca2+Si(−)OSiOCaOOCaOSiSiOCaOOCaOOOHSi(Si3O9H) chainCaO2...

  • Page 165

    150Chapter 4Structure of Concrete1. Edge-sharing calcium octahedrals2. “Dreierkette” form of silicate chains3. Additional calcium octahedrals in special positions on the inversion center to connectdifferent layersAccording to Richardson and Groves (1992), a jennite model can be built up from ...

  • Page 166

    4.3Structure of Concrete in Nanometer Scale: C–S–H Structure151By combining the general formula with 29Si NMR measurement, information about thestructure can be obtained.17O NMR spectroscopy and 29Si NMR have demonstrated the existence of the Ca–OHgroup and Si–OH groups, no matter whether...

  • Page 167

    152Chapter 4Structure of Concretecalcium hydroxide, or it is based on the structure of Ca(OH)2 to some extent. This kind ofstructure, according to the literature, was the one studied most, dating back to the 1960s. It didnot consider the detailed structural characteristics, but some stoichiometry...

  • Page 168

    4.4Transition Zone in Concrete153MicrohardnessDistance from aggregateFigure 4-13Micro hardness distributionTwo methods have been used to identify the existence of the third phase. The first methodis micro-indentation, which is a method used to detect the hardness of a material. A typical curveof...

  • Page 169

    154Chapter 4Structure of Concrete50407000600050004000300020001000Cement pasteConcreteAggregate300020001000Strain (10−6)20100030Stress (MPa)(psi)Figure 4-14Stress–strain behavior of aggregate, concrete, and HCPTable 4-2Permeability coefficients of differentmaterialsTypePermeability Coefficie...

  • Page 170

    4.4Transition Zone in Concrete155of compressive strength as compared to the corresponding HCP and mortar, as shown inFigure 4-14.In addition to the examples above, the existence of the transition zone in concrete can beused to explain why concrete is brittle in tension but relatively tough in com...

  • Page 171

    156Chapter 4Structure of ConcreteTransition zoneBulk cement pasteCSH gelAFtCHFigure 4-15Interfacial zone of concreteformation and extension of matrix cracks under a compressive load. On the other hand, undertensile loading, cracks propagate rapidly and at a much lower stress levels. This is why c...

  • Page 172

    4.5Microstructural Engineering157aspects of cements, such as particle size distribution, relative proportions of the different cementcomponents, and the content and type of gypsum interground with the clinker, are commerciallyfeasible. On the other hand, it is feasible and common to modify variou...

  • Page 173

    158Chapter 4Structure of ConcreteWaterWaterDispersed cement particlesFlocculated cement particlesSuperplasticizersolution filmCement particleCement particleFigure 4-16Flocculated cement and dispersed cementThe physical chemistry behind the flocculated condition has been well established. Cementg...

  • Page 174

    4.5Microstructural Engineering159Cement particle packingDenser binder packing systemLarge cement particleSmall cement particleFiner particleFigure 4-17Packing systems of cement and binderHowever, this happy state of affairs does not usually occur if microsilica is simply added intocement. Early e...

  • Page 175

    160Chapter 4Structure of Concrete4.5.4 Transition zone improvementAs transition has been identified as a weak link in concrete, it has become customary to ascribesome poor performance characteristics of traditional concrete to the transition zone. From thispoint of view, microstructural engineer...

  • Page 176

    4.5Microstructural Engineering16160504030Volume Percentage (%)20100600204080100120Distance (µm)Cement paste matrixSilica fume modified matrixFigure 4-19Porosity distribution of transition zone for two pastes3000250020001500100050000.000.200.40Slip displacement (mm)Load-slip displacement curve co...

  • Page 177

    162Chapter 4Structure of ConcreteOOOOOnRRRRSiOOORRRSiFigure 4-21Unit for improving toughness of concretea special cement system called MDF (macro-defect-free) has been developed. The thin sheetproducts manufactured by MDF show enormously improved strength levels and enormouslymodified microstruc...

  • Page 178

    References163Why must learn the structure of concrete?How can you improve concrete compressive strength from the point of view of microstructure?Can you eliminate the porous interface in concrete?How is the microstructure of concrete influenced by a superplasticizer?Why does modern concrete tech...

  • Page 179

    CHAPTER5HARDENED CONCRETEWith the development of hydration, concrete will change from a fluid to a plastic state, and finallyto a solid hardened state. In the hardened state, concrete is ready to support external loads as astructural material. The most important properties of hardened concrete ...

  • Page 180

    5.1Strengths of Hardened Concrete165Figure 5-1The universal testing machineThe 28-day compressive strength of concrete, determined by a standard uniaxial compres-sion test, is accepted universally as a general concrete property index for structural design. Tomeasure different strengths of concret...

  • Page 181

    166Chapter 5Hardened ConcreteInput variable(reference input)Input variable(reference input)Output variableMeasured outputMeasured outputMeasured outputMeasured outputOutput variablePrescribed functionPrescribed functionPrescribed functionPrescribed functionControllerControllerControlled processCo...

  • Page 182

    5.1Strengths of Hardened Concrete167Displacement (mm)2.5kVoltage (V)10Figure 5-3Relationship between displacement and voltagedisplacement transducer with a full range of 2.5 mm, standard outputs of known displacementvalues can be provided by a micrometer, as shown in following case:Displacement (...

  • Page 183

    168Chapter 5Hardened Concrete(a)(b)(c)(d)Figure 5-4Failure process of a concrete under compression: (a) shear-bond crack(load less than 40% ultimate value); (b) load-initiated cracks (load between 40 and 80%ultimate value); (c) crack concentration (load greater than 80% ultimate value); (d) major...

  • Page 184

    5.1Strengths of Hardened Concrete169equal layers, with each layer being stroked 35 times by a hemispherical-tipped steel rod.After demolding, the specimen should be cured at a temperature of 20± 1◦C and a relativehumidity of more than 90%. However, a cube of standard size is heavy and sometime...

  • Page 185

    170Chapter 5Hardened Concrete(a)(b)(c)Figure 5-6Influence of constraint to failure mode of concrete specimen: (a) withconstraint on both ends; (b) with constraint in one end; and (c) without constraintremainder being in a state of triaxial stress. The effect of this type of end restraint is to g...

  • Page 186

    5.1Strengths of Hardened Concrete171(a)(b)Figure 5-8Two conventionally used uniaxial tension methods: (a) grips dog bone test;(b) end plate loading method(c) Size effect : The probability of having large deficiencies, such as void and crack,increases with size. Thus, smaller-size specimens will ...

  • Page 187

    172Chapter 5Hardened Concrete(a)(b)(c)Figure 5-9Failure process of concrete specimen under tension: (a) random crackdevelopment (after 30% peak load is reached); (b) localization of microcracks (after80% peak load is reached); and (c) major crack formation and propagationmicrocracks occur randoml...

  • Page 188

    5.1Strengths of Hardened Concrete1735.1.3.3 Relationship between compressive strength and tensile strengthIt has been pointed out before that other mechanical properties of a concrete can be relatedto its compressive strength. However, there is no direct proportionality between tensile andcompres...

  • Page 189

    174Chapter 5Hardened ConcretePPσ1σ1σ1, maxσ2T2 0−4−8−12 −16σ1, max = 2PπLDFigure 5-11Stress distribution of the specimen under the splitting testFigure 5-12Experimental setup of indirect tension test on a cube specimenindirect tensile strength for the cube specimen isfst= σten=2Pπ...

  • Page 190

    5.1Strengths of Hardened Concrete175Span length, L25 mm. min.L/3L/3L/3L/3Figure 5-13Flexural strength test setup for hardened concreteallows a beam size of 100× 100× 500 mm when the maximum size of aggregate is less than25 mm. The arrangement for the modulus of rupture test is shown in Figure 5...

  • Page 191

    176Chapter 5Hardened ConcreteIIIIIIIVσ1σ2σ2σ2σ2σ1σ1σ1IIIIIIIV00.2−0.20.40.60.81.01.21.400.20.40.60.81.01.21.4σ1/fc'σ2/fc'fc'(psi)270044508350Figure 5-14Behavior of concrete under biaxial stress5.1.5 Behavior of concrete under multiaxial stresses5.1.5.1 Behavior of concrete under biaxi...

  • Page 192

    5.1Strengths of Hardened Concrete177Figure 5-15Reinforced concrete panel under biaxial stress (University of Houston)from 200 to 400µε. In biaxial tension– compression, the magnitude at failure of both the principalcompressive and tensile strain decreases as the tensile stress increases. In b...

  • Page 193

    178Chapter 5Hardened ConcreteFigure 5-16Triaxial testing machine at Dalian University of TechnologyImproved deformation capacityCFTHigher yield strengthSRCEccentric deformation, δSeismic force, QFigure 5-17Comparison of the loading behaviorswhere ftri–c is the compressive strength of concrete ...

  • Page 194

    5.1Strengths of Hardened Concrete179ConcreteSteel tubeSteel tubeMain reinforcementSpiral stirrup(a)(b)Figure 5-18Confinement for concrete column in the form of (a) a spiral, and (b) a tubeSide ViewFiberSpoolsView from TopConcreteColumnDownward Movement + Counter-clockwise Rotationto Wrap Fiber a...

  • Page 195

    180Chapter 5Hardened ConcreteaxLAggregatePInterfacial zoneBulk pastePPmPySlip displacementFigure 5-20Model for the bond between aggregate and matrix5.1.6 Bond strengthBond strength is defined as the shear strength between the aggregate, fiber, reinforcing steel,and cement paste. The bond streng...

  • Page 196

    5.1Strengths of Hardened Concrete181in which the subscript comma indicates differentiation. The quantityω is defined asω=kEaA(5-18)Equation 5-17, together with boundary conditions and continuity conditions, constitute a completeset of equations for the determination of U(x). Solving this set o...

  • Page 197

    182Chapter 5Hardened ConcreteLVDTLVDTSpecimenHollowcylinderCircularplateSteel rodPFigure 5-21Bond strength test setupNote that an additional equation is needed to determine the debonding length, a:P ∗max0.5 (ωa)2+ cosh2 [ω (L− a)]+ ωa sinh [ω (L− a)] cosh [ω (L− a)]ωa+ sinh [ω (L...

  • Page 198

    5.1Strengths of Hardened Concrete183Pushout load curveTop LVDT slip displ.Bottom LVDT slip displ.Time duration (sec)Displacement (mm)Force (N)50010001,5002,0002,500050010001,5002,0002,50000.00.20.40.60.8IIIIIIFigure 5-22Push-out force and displacement as a function of timeVariable embedded length...

  • Page 199

    184Chapter 5Hardened Concrete(b)(a)(c)(d)Cement pasteAggregateFigure 5-24Different types of bond test configurations: (a) aggregate pullout test; (b)shear-type test; (c) tension-type test; and (d) bending-type test5.1.7 Fatigue strengthThere are two terms regarding fatigue in concrete technology...

  • Page 200

    5.1Strengths of Hardened Concrete185Increasing test duration ordecreasing rate of loadingUsual short-term strengthStatic fatigue failure envelopeStress/strength ratio0.20.40.60.81.01.20(Strain× 10−6)1,000 2,000 3,000 4,000 5,000 6,0008,0007,000Figure 5-25Influence of loading rate on load-carr...

  • Page 201

    186Chapter 5Hardened ConcretePPPMσyσyσyσyσyσyσyyytttyxxxxxxxx00000www(w− d)/2wdw(a)(b)(yielding)(yielding)(c)S =wtS =w2tS =(w− d)tSktSktSSSP6MFigure 5-27Comparisons between S andσof convenience, while true stress is determined according to the real materials states (stressconcentratio...

  • Page 202

    5.1Strengths of Hardened Concrete187800700600500400103104105106107108kt = 1Sm = 0Cycles to failure, NfStress amplitude, Sa(MPa)Figure 5-28An S-N diagramfound to be a straight line on a log– log plot, the relationship between stress amplitude andfatigue cycles can be written asσar= A(Nf)B(5-30)...

  • Page 203

    188Chapter 5Hardened ConcreteIf more than one amplitude or mean level occurs in a fatigue test, the fatigue life may be estimatedby summing the cycle ratios, called the Palmgren-Miner rule:NiNfi= 1(5-35)where Ni is the number of applied cycles underσi orσai, and Nfi is the number of cycles to...

  • Page 204

    5.2Stress–strain Relationship and Constitutive Equations18910060804020106 cycles0100608040200Minimum stress as a percentof static strengthMinimum stress as a percentof static strengthFigure 5-29A fatigue design diagram (ACI 215R-74)where ai is the initial crack size obtained from inspection (if...

  • Page 205

    190Chapter 5Hardened Concreteare used to measure the deformation. If a very stiff machine is being used, for normal-strengthconcrete, the stroke control is good enough to obtain the post-peak response. However, forhigh-strength concrete, the stroke control cannot determine sufficient downward mo...

  • Page 206

    5.2Stress–strain Relationship and Constitutive Equations191SpecimenExtensometerFigure 5-32Notched specimen used for uniaxial tension testthis way unstable failure near the peak load (resulting from the sudden release of stored elasticenergy) is avoided. The load shared by the concrete is obtain...

  • Page 207

    192Chapter 5Hardened ConcreteLVDT2413PZTFigure 5-33Uniaxial tension test setup for unnotched concrete specimenTensile Strength (MPa)5432100.0200.040.060.080.1Displacement (mm)Figure 5-34The stress–deformation curve of unnotched concrete specimensignals from the AE transducers provide valuable i...

  • Page 208

    5.2Stress–strain Relationship and Constitutive Equations193elastic part is characterized by uniform deformation and “global” behavior of the material. Inthe second part, due to the damage (indicated by the occurrence of AE events) in the specimen,the modulus of the material starts to reduce...

  • Page 209

    194Chapter 5Hardened Concretein which, E sh is the modulus of elasticity of concrete in compression, P0 the load correspondingto a stress level of 5 MPa, P the load corresponding to 0.4 fc, A the area over which the loadis applied, l the measuring length, andδn the mean value of the deformation ...

  • Page 210

    5.2Stress–strain Relationship and Constitutive Equations195AggergateMatrix(a)(b)(c)Figure 5-37The square-in-square model: (a) the discrete system; (b) the representa-tive volume; and (c) the sliced system(b) Series model (isostress model): In this kind of model, it is assumed that the force int...

  • Page 211

    196Chapter 5Hardened ConcreteIt should be noted that in all the above equations, MPa is used for strength and stress, and GPafor Young’s modulus.5.2.3 Constitutive equationsA constitutive equation is a relation between two physical quantities that describes the response ofa material or substanc...

  • Page 212

    5.3Dimensional Stability—Shrinkage and Creep197whereσc is the compressive stress,σc,u the ultimate compressive stress,εc the compressivestrain, andεc,u the strain corresponding toσc,u. By using the exponential power series expansion,Equation 5-60 can be rewritten asσc=2.7182Ec,u εc1+εc...

  • Page 213

    198Chapter 5Hardened ConcreteFigure 5-39Formation of plastic shrinkage crackPlastic shrinkage usually leads to a downward movement of the solid and heavier ingredi-ents in the surface layer. This downward movement may be resisted by the large size of coarseaggregates or by the top layer of reinfo...

  • Page 214

    5.3Dimensional Stability—Shrinkage and Creep199described in the 1930s by Lyman (1934) as a factor contributing to the total shrinkage. However,in the earlier days, it was noted that autogenous shrinkage occurred only at very low w /c ratios,far below the practical w /c range, and did not draw m...

  • Page 215

    200Chapter 5Hardened Concrete50 mmStrain gaugeFilmThermometer100 mmSpecimenSteel moldTeflon sheetFigure 5-41Method of measuring autogenous shrinkage of cement pastevolume or chemical shrinkage. When the hydration products percolate to form a structuralskeleton, autogenous shrinkage can be restrai...

  • Page 216

    5.3Dimensional Stability—Shrinkage and Creep201Figure 5-42Absorbed water filmThree basic mechanisms are responsible for the shrinkage of Portland cement concrete.One is the disjointing pressure that is related to the water absorbed on the surface of C–S–H.Water is absorbed in the layers of...

  • Page 217

    202Chapter 5Hardened Concretewhere pc is the capillary pressure of water in a pore, pv is the vapor pressure, andp is thesuction pressure. By substituting the Kelvin equation into the Laplace equation, we getp=−νRTMln(RH)=−ln(RH)K(5-68)From this equation, it can be seen that suction pressure...

  • Page 218

    5.3Dimensional Stability—Shrinkage and Creep203TL'LTFigure 5-44Shrinkage crack generated by restraintpermits the passage of water, is detrimental to appearance, reduces shear strength, and exposesthe reinforcement to the atmosphere.The magnitude of the ultimate shrinkage is primarily a function...

  • Page 219

    204Chapter 5Hardened ConcreteFigure 5-45Free-drying shrinkage measurement using a Demac gage on a cylinderspecimenSpecimenSteel ringWood basePlanAraldite sealerSection I-I 375 mm305 mm254 mm140 mmFigure 5-46Ring-shaped specimen for restrained shrinkage testis associated with geometry and non-stre...

  • Page 220

    5.3Dimensional Stability—Shrinkage and Creep205Figure 5-47Elliptical ring test for constrained shrinkageat a more predictable position. The test apparatus not only can discriminate the extension ofmortar or concrete in a short time, but also can lead to an early shrinkage crack. Therefore,the n...

  • Page 221

    206Chapter 5Hardened ConcreteMoreover, SRA can reduce the long-term drying shrinkage by 50%, and there is a significantimprovement in the restrained shrinkage performance. Even for concrete with proper curing atwhich the drying shrinkage would reduce to a minimum, there is still a substantial re...

  • Page 222

    5.3Dimensional Stability—Shrinkage and Creep207High loading rateIntermediate loading rateLow loading rateεσFigure 5-49Hysteresis behavior under high and low loading ratesFinal deflection ∆FInitial deflection ∆I∆F/∆I = 2–3Figure 5-50The long-term deformation of reinforced concrete be...

  • Page 223

    208Chapter 5Hardened ConcreteReinforcingsteel∆lRC =∆lC =∆lSFigure 5-51Parallel model for a reinforced concrete columnmake sure that sufficient prestress can be applied. Moreover, in some cases, restressing of theprestressed tendon has to be carried out to compensate the stress caused by cr...

  • Page 224

    5.3Dimensional Stability—Shrinkage and Creep209particles are chemically bonded, no slip can occur. If only van der Waals interaction exists, slipcan occur under some conditions. For instance, when there is a sufficient thickness of waterlayers between the C–S–H particles, the water can red...

  • Page 225

    210Chapter 5Hardened ConcreteEηFigure 5-53Maxwell model(time-independent) part is represented by a spring with modulus E , and the viscous (time-dependent) part is represented by a dashpot of viscosityη. The equations regarding theequilibrium, compatibility, and constitutive relationship are as...

  • Page 226

    5.3Dimensional Stability—Shrinkage and Creep211Stress, σStress, εTime, tTime, tt1t1Figure 5-54Creep behavior under constant stress for the Maxwell modelThe strain will stay constant for t> t1. The stress and strain are plotted against time asshown in Figure 5-54.(2) Relaxation behavior (co...

  • Page 227

    212Chapter 5Hardened ConcreteEηFigure 5-56Kelvin-Voigt model(1) Creep behavior under constant stress applied from 0< t< t1. The governingequation is a first-order differential equation, which can be solved by the followingprocedures. Multiplying each side of the governing equation by exp ...

  • Page 228

    5.3Dimensional Stability—Shrinkage and Creep213The above behavior is illustrated in the second part of the curve shown in Figure 5-57b.(2) Relaxation behavior (constant strain applied at t= 0). At t= 0, the dashpot istheoretically rigid. In other words, the strain should be zero. To force the s...

  • Page 229

    214Chapter 5Hardened ConcreteStress,σStress,εTime, tTime, t1 + 211 + 2 + 3123Figure 5-60Illustration of the superposition principlea nonconstant stress can be obtained by superposition, as illustrated in Figure 5-60. To applysuperposition, any increase in stress level is replaced by a new const...

  • Page 230

    5.3Dimensional Stability—Shrinkage and Creep215Figure 5-62The experimental set-up for measuring creepwhere C t is the creep value at time t (in days) after being loaded, D a constant, and C u theultimate creep.5.3.3 Test method for creepThe experimental setup for measuring creep is shown in Fig...

  • Page 231

    216Chapter 5Hardened ConcreteperimeterAAAFigure 5-63Three shapes with same section area but different perimeter(d) Theoretical thickness: The theoretical thickness is defined as the ratio of the section areato the semi-perimeter in contact with the atmosphere, as shown in the following equation:...

  • Page 232

    5.4Durability217(Ulm et al., 2000; Sun et al., 2002; Le Bell´ego et al., 2003; Kuhl et al., 2004; Nguyen et al.,2007). As a result of durability studies, many countries have proposed durability-based designguidelines (DuraCrete, 2000; CCES, 2004; MDPRC, 2007).5.4.1 Causes of deterioration and ma...

  • Page 233

    218Chapter 5Hardened ConcreteTable 5-2Typical values of permeability coefficients of concrete materialsTypePorosity(%)Average Pore SizePermeability CoefficientHCP20100 nm6× 10−12 cm/secAggregate3– 1010µm1–10 × 10−12 cm/secConcrete20– 40nm– mm100– 300× 10−12 cm/secpaste is of...

  • Page 234

    5.4Durability219Hence, the solution of the second Fick’s law for a semi-infinite plane has the formC(x, t)= C0 1− erfx2√Dt(5-97)where C (x , t ) is the ion or gas concentration at distance x and time t , C 0 the ion or moistureconcentration at the higher concentration surface, and erf the ...

  • Page 235

    220Chapter 5Hardened ConcreteFigure 5-66Permeability cella condition in a year. Hence, the considerable length of time required for testing the concreteand the difficulties of attaining a steady-state outflow can be regarded as disadvantages for thesteady-flow method.In cases of good-quality c...

  • Page 236

    5.4Durability221Figure 5-67Penetration depth test with an autoclavewhere x is the depth of penetration of concrete (m), v the fraction of the volume of concreteoccupied by the pores, and T the time duration under pressure (sec). The value of v representsdiscrete pores, such as air voids, which ar...

  • Page 237

    222Chapter 5Hardened ConcreteFigure 5-68Rapid chloride permeability test setupTable 5-3Classification of concrete quality using chlorideion penetrabilityCharge Passed (Coulombs)Chloride Ion Penetrability>4000High2000– 4000Moderate1000– 2000Low100– 1000Very low<100Negligiblemounting t...

  • Page 238

    5.4Durability223100 mmAB100 mm100 mmconcretespecimenCa(OH)2Ca(OH)2+NaClFigure 5-69Measurement of diffusivity coefficientA typical curve of chloride concentration in chamber B obtained from an experiment has astrong nonlinearity between the chloride concentration and time initially. However, afte...

  • Page 239

    224Chapter 5Hardened Concreteby providing points of easy access to the body of the concrete to aggressive agents that mightotherwise not seriously affect the material.5.4.5.1 Cause of crackingTable 5-4 summarizes the kinds of cracking that can occur due to interactions in the concretematerials an...

  • Page 240

    5.4Durability225Table 5-5Type of cracking in concrete structuresNature of CrackCause of CrackingRemarksLarge, irregular, frequently withheight differentialInadequate support,overloadingSlabs on ground, structural concreteLarge, regularly spacedShrinkage cracking,thermal crackingSlabs on ground, s...

  • Page 241

    226Chapter 5Hardened Concretebreakdown of the passive film on the steel, and carbonation-induced corrosion is caused by ageneral breakdown of passivity by neutralization of the concrete.5.4.6.1 Carbonation-induced corrosionCarbonation occurs due to the penetration of carbon dioxide from the atmo...

  • Page 242

    5.4Durability227important parameter controlling the rate of carbonation (Bentur et al., 1997). The quality of theconcrete is a function of the composition of the binder (i.e., whether Portland cement or blendedcement was used), the water/cement ratio, the water/binder ratio, and the curing condit...

  • Page 243

    228Chapter 5Hardened Concreteas large as six and half times the original Fe. This expansion creates cracking and spalling insidethe concrete, and finally destroys the integrity of the structural concrete and causes failures ofbuildings and infrastructures.As a result, chloride-induced corrosion ...

  • Page 244

    5.4Durability229corrosion of reinforcing steel can be very large. For example, a survey by the China Academy ofEngineering in 2002 reported that the annual cost due to corrosion of reinforcing steel in Chinareached 100 billion Chinese Yuan. So it is desirable to know clearly the mechanism of corr...

  • Page 245

    230Chapter 5Hardened Concretewith the necessary notations of chemical reactions. At the anode site, the iron dissociates to formferrous ions and electrons:Fe→ Fe2+ + 2e−(anodic reaction)(5-105)The electrons move through the metal toward the cathodic site but the ferrous ions are dissolvedin t...

  • Page 246

    5.4Durability231judge the possibility of corrosion. A big drawback is that half-cell potential is highly dependenton the condition of the concrete at the time of measurement. For instance, moist concrete willyield different measurements from dry concrete.The application of the acoustic emission (...

  • Page 247

    232Chapter 5Hardened ConcreteBy substituting Equations 5-110 and 5-111 into 5-114, we can obtain the pressure expressionasp=4µcµs2µs+ (ks− 1)aa(5-115)The stress produced at surrounding concrete interface is then derived asσθθ=4µsµc2µs+ (ks− 1) µcaa= Caa(5-116)For steel, the shear mo...

  • Page 248

    5.4Durability233poor performance. Thus, training is necessary for properly producing, handling, and applyingthe coating, and repairing field damage to epoxy-coated bars. Moreover, the bond propertiesbetween the concrete and the epoxy-coated rebars are not as strong as between concrete andconvent...

  • Page 249

    234Chapter 5Hardened Concreteleads to severe cracking thereafter. Two general types of attacks can occur (Tang, 1987): (1)alkali –carbonate attack with dolomitic limestone aggregate (some argillaceous dolomites) iscalled an alkali –carbonate reaction (ACR), and (2) alkali –silica attack wit...

  • Page 250

    5.4Durability235The degree of AAR is affected by (1) presence of water—if there is no water, there is noexpansion; (2) alkali content—if the alkali content (Na2O and K2O) is less than 0.6%, there isno reaction, and concrete containing more than 3 kg/m3 of alkali can be considered to have ahig...

  • Page 251

    236Chapter 5Hardened Concretethe expansion of test specimens has been considered to be the most dependable way to evaluateaggregate reactivity, and a number of test procedures have been devised. The testing methodscommonly used include standard test methods, such as the mortar bar test (ASTM C227...

  • Page 252

    5.4Durability237In the gel fluorescence test method, a 5% solution of uranyl acetate is applied on the surface ofthe specimen, then the specimen is viewed under an ultraviolet (UV) light. A yellowish greenfluorescent glow means that AAR is present. Since AAR can cause significant deterioration...

  • Page 253

    238Chapter 5Hardened Concrete5.4.8 Deterioration caused by freeze-thawingConcrete is a porous material. As the cement and water in fresh concrete react to form a hardenedpaste binding the coarse and the fine aggregates together, voids are left in the originally water-filled space among the ceme...

  • Page 254

    5.4Durability239water in the capillary pores due to the volume expansion of ice. Such pressure, if not relieved,can result in internal tensile stresses that may cause local failure of the concrete. On subsequentthawing, the expansion caused by ice is maintained so that there is now new space avai...

  • Page 255

    240Chapter 5Hardened Concrete5.4.9 Degradation caused by sulfate attackSulfate attack is one of main factors causing deterioration of concrete durability. It is generallyregarded as an expansion due to the reaction of sulfate with some hydration products in cementpaste. Portland cement itself con...

  • Page 256

    5.4Durability241sulfate (MgSO4) reacts to form gypsum and destabilizes C–S–H, the strength-governing phase incement paste. This is because Mg2+ and Ca2+ ions associate well, since they have equal valenceand similar ionic radii, which can lead to a reaction between magnesium sulfate and the C...

  • Page 257

    242Chapter 5Hardened ConcreteThe resistance of concrete to sulfate attack depends primarily on the permeability anddiffusivity of the concrete, the type and amount of cement in the concrete, and the type andamount of mineral additives in the concrete. Low permeability and diffusivity provide the ...

  • Page 258

    5.4Durability243ConcreteReinforcing steelCracking due tocorrosion of steelCracking due tofreezing and thawingPhysical abrasion due towave action, sand andgravel and floating iceChemical decompositionof hydrated cementChemical decompositionpattern: 1. CO2 attack2. Mg ion attack3. Sulfate attackAtm...

  • Page 259

    244Chapter 5Hardened ConcreteFigure 5-77Seawater tank for marine environmental simulation test(Mehta, 1980). Low permeability can reduce the penetration of salt, sulfate, and water; besides,low-permeability concrete normally has high strength and good erosion resistance to the marineenvironment. ...

  • Page 260

    5.4Durability245Figure 5-78Themarineexposuretest siteinQingdao, China

  • Page 261

    246Chapter 5Hardened Concretefactors. Many researchers have undertaken studies along this direction. For example, Sun et al.(1999, 2002) have conducted experiments on concrete with a combination of loading, chloridediffusion, and freeze– thaw to investigate the coupling effect on performance. H...

  • Page 262

    Problems2472. A specimen of shrinkage-compensating concrete of 0.25× 0.25× 2.5 m is made with 12 steel rebars(12 mm in diameter) inside of the same length. The specimen expands during the wet curing period. IfEc= 15 GPa, Es= 200 GPa, and free expansion strain= 0.0003 at the time, estimate the f...

  • Page 263

    248Chapter 5Hardened Concrete250 mm250 mm100 mmRepaired polymer concreteFigure P5-6REFERENCESAllen, R.T.L., Edwards, S. C., and Shaw, J.D.N. (1993) The repair of concrete structures, London: BlackieAcademic & Professional.Alonso, C. and Andrade, C. (1994) “Lifetime of rebars in carbonated c...

  • Page 264

    References249Clifton, J. R., Beeghley, H. F., and Mathey, R. G. (1975) “Nonmetallic coatings for concrete reinforcingbars,” Building Science Series 65, U.S. Department of Commerce, National Bureau of Standards.Damidot, D., Nonat, A., and Barret, P. (1990) “Kinetics of tricalcium silicate hy...

  • Page 265

    250Chapter 5Hardened ConcreteMinistry of Development of the People’s Republic of china () (2007) Chinese DesignCode of Concrete Structure Durability ().Mitsui, K., Li, Z., Lang, D., and Shah, S.P. (1994 “Relationship between microstructure and mechanicalproperties of the paste– aggregate in...

  • Page 266

    CHAPTER6ADVANCED CEMENTITIOUSCOMPOSITESIn this chapter, the advanced cement-based composites, such as fiber-reinforced concrete, polymer-modified concrete, ultra-high-strength concrete, self-compacting concrete, and engineered cementcomposites, are introduced. Most of them have been developed r...

  • Page 267

    252Chapter 6Advanced Cementitious Composites0.000.020.040.060.080.10012345Steel fiber(0.5% in volume)Polypropylene fiber(0.5% in volume)Plain concreteTensile strength (MPa)Displacement (mm)Figure 6-1Load– displacement curvesIn conventional applications of fiber cementitious composites, usually...

  • Page 268

    6.1Fiber-Reinforced Cementitious Composites2536.1.2 Factors influencing the propertiesThe properties of fiber-reinforced, cement-based composites can be influenced by many param-eters, such as fiber type, fiber amount, matrix variation, and manufacturing methods. In thissection, these parame...

  • Page 269

    254Chapter 6Advanced Cementitious CompositesCrimped-end wire(Hooked)Flattened-end slitsheet / wireMachined chipStraight slit sheet or wireDeformed slit sheet or wireFigure 6-2Different shapes and surface textures of steel fibersfiber to 1.8 for a low-modulus fiber. The stronger fibers are ass...

  • Page 270

    6.1Fiber-Reinforced Cementitious Composites255whereσcu= ultimate stress in fiber-reinforced concreteσmu= ultimate stress in the matrixoσf= stress in the fiberEm= Young’s modulus of matrixεmu= ultimate strainVm= matrix volume ratioVf= fiber volume ratioFor a high fiber volume fraction, t...

  • Page 271

    256Chapter 6Advanced Cementitious Compositesincrease the bond properties with the fibers, improve the matrix toughness, and enhance thematrix tensile strength and, hence, the mechanical properties of FRC.(d) Processing methods: Recent studies have shown that the response of fiber-reinforcedcomp...

  • Page 272

    6.1Fiber-Reinforced Cementitious Composites257Figure 6-6The extrusion processproducts formed under high shear and high compressive forces are denser and stronger, fiberalignment is controllable, and the product shape is flexible and good for mass production. Withproperly designed dies and prope...

  • Page 273

    258Chapter 6Advanced Cementitious Compositesthick) and made a significant improvement in extrudate formulas. Generally speaking, the matrixformed through the extrusion process is dense and good in flexural strength. It can provide aseal effect for the phase-changing materials.6.1.3 Fiber – ce...

  • Page 274

    6.1Fiber-Reinforced Cementitious Composites259(0.25 in.) in diameter. The loading fixture is connected to the servo hydraulic actuator and theentire specimen fixture moves with the actuator. A restraining frame that can make contact withthe specimen’s brass guide plates is connected to a load...

  • Page 275

    260Chapter 6Advanced Cementitious CompositesFigure 6-9Typical pullout fibers from a three-point bending test6.1.4 Mechanical propertiesAs mentioned earlier, the incorporation of fibers into cement-based composites mainly improvestheir toughness, bending, and tensile properties. In this section,...

  • Page 276

    6.1Fiber-Reinforced Cementitious Composites261OAσBCD123Stage 4εFigure 6-10Strain-hardening behavior of steel fiber-reinforced cementitiouscompositedispersed at end of this stage. Stage 2 is from A to B. In this stage, randomly distributed microc-racks start to localize and form the first majo...

  • Page 277

    262Chapter 6Advanced Cementitious CompositesThe steel fiber used has a length of 32 mm, and an equivalent diameter of 0.8 mm with a tensilestrength of 810 MPa and Young’s modulus of 200 GPa.It can be seen from the figure that with the increase of the fiber volume fraction ratio, notonly is t...

  • Page 278

    6.1Fiber-Reinforced Cementitious Composites263Deflection (mm)Flexuralstress (MPa)Without fly ashWith fly ash03214035302520151050Figure 6-13Stress–deflection curves of an extruded FRC thin plateFiber-reinfored beamUnreinforced matrix beam(closed-loop testing system)It =Aera OABFAera OAKLI(ACI) ...

  • Page 279

    264Chapter 6Advanced Cementitious CompositesPDeflectionFiber-reinforcedbeamBCDEJOIHGLVDT or dial gaugeZeroloadcapacityI5 =Area OABCIArea OAJI10 =Area OABDHArea OAJI30 =Area OABEGArea OAJ3d5.5d15.5dTotal Load, PdAFigure 6-15Definition of toughness index by ASTMLVDT or dial gaugePDeflectionADCBOFi...

  • Page 280

    6.1Fiber-Reinforced Cementitious Composites265Figure 6-17Hybrid macrofiber- and microfiber-reinforced cementitious compositeto optimize their advantages. For example, by incorporating micro- and macrofibers into acement-based composite at same time, the microfibers can restrain the developmen...

  • Page 281

    266Chapter 6Advanced Cementitious Composites0043213530252015105Deflection (mm)Flexural stress (MPa)Glass: PP:PVA40:0:6020:40:4040:20:40Total Vf = 5%20:80:0Figure 6-18Flexural response of hybrid composites combing glass/PP/PVA fibers(Peled, et. al., 2000)Fiber-reinforced mortar : Since mortar con...

  • Page 282

    6.1Fiber-Reinforced Cementitious Composites267fibers contribute not only directly to the compressive resistance of the composite throughparallel support, but also indirectly to the resistance through the confining effect on thematrix. The flexural strength of SIFCON can reach 60 MPa, which is ...

  • Page 283

    268Chapter 6Advanced Cementitious CompositesFigure 6-19Extruded heat insulation productsFigure 6-20Extruded imitation wood-productsFigure 6-21Extrusion process in a plant

  • Page 284

    6.1Fiber-Reinforced Cementitious Composites269Figure 6-22Extruded products can be easily machined (milling)Figure 6-23Industry-extruded products with several different functionsshown in Figure 6-22. Other industrial extruded products include functional blocks with cablechannels and a heat insulat...

  • Page 285

    270Chapter 6Advanced Cementitious CompositesFigure 6-24Industry-extruded wall panel with heat insulation coreAnother popular product of fiber-reinforced cement-based composites, the engineeringcement composite (ECC), is introduced in detail in a later section.6.2 HIGH-STRENGTH CEMENTITIOUS COMPO...

  • Page 286

    6.2High-Strength Cementitious Composites271The w /c or w /b ratio is a key parameter in making high-strength concrete. From Abrams’law and the gel space ratio introduced earlier, it is easily seen that a low w /c or w /b ratiocan lead to high compressive strength. Thus, the basic measure usuall...

  • Page 287

    272Chapter 6Advanced Cementitious Composites0510152025300102030405060708090NSCHSCCompressive Strength (MPa)Age (day)Figure 6-25Compressive stress development of normal-strength concrete (NSC) andhigh-strength concrete (HSC)LoadNormal concreteHigh strength concreteLoadFigure 6-26Failure mode of no...

  • Page 288

    6.2High-Strength Cementitious Composites273Table 6-4Effectiveness of microsilica in reducing permeability of concreteCementWDRAaMicrosilicaWater-to-PowderPermeabilityContent (Lb/Yd3)(wt.%)(wt.%)RatioCoefficient, K (m/s)170002.38120× 10−10170102.091160× 10−101700102.3210× 10−101701102.10...

  • Page 289

    274Chapter 6Advanced Cementitious Compositesthe presence of equal amounts of chloride ions is the same regardless of the microsilica contentof the concrete; i.e., there is no negative influence of microsilica to nullify or outweigh thebeneficial effects of a refined pore structure.The effectiv...

  • Page 290

    6.2High-Strength Cementitious Composites2750204060801101001,00010,000Pore radius (nm)Relative volume (%)without SF at 7-daywithout SF at 63-daywith SF at 7-daywith SF at 63-dayFigure 6-27Effects of the addition of silica fume on pore size distribution06012018024007142128Curing time (days)Compress...

  • Page 291

    276Chapter 6Advanced Cementitious CompositesTable 6-5Temperature resistance of DSPTemp.Wt. LossFlexural StrengthFlexural StrengthVac. Leak RateVac. Leak Rate(◦C)(%)(psi) before PI(psi) after PI(torr/min) before PI(torr/min) after PI2004.54,6504,8500.1n/a3005.04,2004,9006.004006.23,8506,55011.00...

  • Page 292

    6.2High-Strength Cementitious Composites277Table 6-6Compositions of representative MDF materialsConstituentParts of WeightWeight %Volume %Calcium aluminate cement10084.365.2Polyvinyl alcohol/acetate75.912.3Glycerin0.70.61.4Water119.321.1When the polymer is removed by heating at high temperature, ...

  • Page 293

    278Chapter 6Advanced Cementitious CompositesTable 6-8Characteristics of conventional concrete, high-strength concrete, and ultra-high-strengthconcreteConventionalConcreteHigh-StrengthConcreteUltra-High-StrengthConcreteCompressive strength(MPa)<50∼100>200Water– binder ratio>0.5∼0.3&...

  • Page 294

    6.2High-Strength Cementitious Composites279or negligible presence of Portlandite because of the pozzolanic reaction of a large amount ofsilica fume. By using mercury intrusion porosimetry, it was also found that UHSC has (4) a lowporosity (1 to 3%) as a result of the low w /b ratio and pozzolanic...

  • Page 295

    280Chapter 6Advanced Cementitious Composites5000250102030Fr(MPa)405060C40RPC200Fiber reinforced concreteFr750ε(×10−6 m/m)125010001500Figure 6-31Flexural strength comparisonFigure 6-32The thin-shelled canopies of the Shawnessy Light Rail Train Station inCalgary, Canadaof UHSC. As shown in Figu...

  • Page 296

    6.3Polymers in Concrete281Figure 6-33Application of UHSC in Pavement Cover Plate in high speed railway inChinaFigure 6-34Fiber influence on UHSC impact resistanceThe fibers used in UHSC are usually special steel fibers 12 mm long and 0.2 mm in diameter,originally used in rubber tire production...

  • Page 297

    282Chapter 6Advanced Cementitious Composites6.3.2 Polymer concretePolymer concrete (PC) is produced by premixing a two-part polymer system, composed ofmonomers or prepolymers together with hardeners (cross-linking agent), which is then addedto aggregates to produce a hardened plastic material wit...

  • Page 298

    6.3Polymers in Concrete283particularly suited for bridge overlays. Polymer concrete is especially suitable for areas subjectto chemical attack.Polymer concrete is mixed, placed, and consolidated in a manner similar to conventionalconcrete. With some harsh mixtures, external vibration is required....

  • Page 299

    284Chapter 6Advanced Cementitious CompositesTable 6-10Characteristics of different latexesLatex TypeAcronymSolids (%)Viscosity (cps)MFFTa (◦C)pHStyrene– butadieneSB4720– 501210Acrylic copolymersPAE4720– 10010– 129– 10Styrene acrylic copolymersSA4875– 500010– 186– 9Polyvinyl acet...

  • Page 300

    6.3Polymers in Concrete2850.30.40.50.60.700.10.2SB latex solids/cement ratioWater/cement ratioslump = 150 nmslump = 100 nmslump = 50 nmFigure 6-35Workability of styrene/butadiene latex improved concretemortar and 4–6% for concrete. The entrained air voids act as a lubricant and hence improve th...

  • Page 301

    286Chapter 6Advanced Cementitious CompositesFigure 6-36Casting of disk-like specimens for pull-off strength measurementFigure 6-37Measurement of pull-off strength using a pull-off testerlatexes exceed the bond strength of the unmodified control by factors of 2– 3. The pore-sealingeffects of la...

  • Page 302

    6.3Polymers in Concrete287Figure 6-38Casting of prisms for slant shear measurementTable 6-11Permeability of different types of concretePermeability RatingCharge Passed (C)Type of ConcreteHigh>4000High water/cement, conventional (>0.6) PCCModerate2000– 4000Moderate water/cement, convention...

  • Page 303

    288Chapter 6Advanced Cementitious CompositesFigure 6-39Casting of cubic specimens for determination of compressive strengthTable 6-12Typical mechanical properties of concretes containing polymersPCLMCPICPolymerizedPolyester(MMA)aControlLMCMMAContainingImpregnatedStyreneThermal-Polymer/Agg.MoistAi...

  • Page 304

    6.3Polymers in Concrete289LMC can be used for emergency concreting jobs in mines, tunnels, ceramic tile adhesivesand grouting, swimming pool finishes, and industrial floor toppings, as well as the production ofhigh-strength precast products. As a coating, it has been used for basement and exter...

  • Page 305

    290Chapter 6Advanced Cementitious CompositesTable 6-13Typical mixture proportioning of mortar and concrete modified with latexMortar Parts by WeightConcrete Parts by WeightPortland cement1.001.00Sand3.502.50Stone—2.00Latex, 48% solids0.310.31Water0.240.24Flow, ASTM C230, cm120Slump, ASTM C143,...

  • Page 306

    6.3Polymers in Concrete291Table 6-14Physical properties of typical products used in concrete roadway repairsEpoxy ResinGrouts, Mortars,and ConcretesPolyester ResinGrouts, Mortars,and ConcretesCementitiousGrouts, Mortars,and ConcretesPolymer-ModifiedCementitiousSystemsCompressive strength(MPa)55...

  • Page 307

    292Chapter 6Advanced Cementitious CompositesTable 6-15Testing methods for evaluating the performance ofrepair mortarsTestMethod of TestingDetermination of compressive strengthBS 6319-2:1983Measurement of pull-off strengthBS 1881-207:1992Determination of shear strengthBS En 12615:1999Measurement o...

  • Page 308

    6.4Shrinkage-Compensating Concrete293Original stateWithout constraint,shrinkage on dryingExpansion puts steel in tension,but concrete in compressionStress loss due to shrinkageUnder constraint, tensilestress develops; cracks happenPortland cement concreteType K cement concreteResidual expansion...

  • Page 309

    294Chapter 6Advanced Cementitious Composites1221300±0.5j10355±0.58R3±0.0099.5±0.5099.5±0.501-Steel plate2-RebarUnit (mm)Figure 6-41A restrained frame for expansion rate measurement on concreteTable 6-16A typical mix proportion of shrinkage-compensating concrete (kg/m3)SeriesBinderCoarse Aggr...

  • Page 310

    6.4Shrinkage-Compensating Concrete295the temperature of the concrete mixture to below 29◦C. Because of the quicker stiffeningand setting of expansive concrete under hot and windy conditions, plastic shrinkage crackseasily occur and create more serious problems than normal Portland cement. Hence...

  • Page 311

    296Chapter 6Advanced Cementitious Composites6.5 SELF-COMPACTING CONCRETESelf-compacting concrete (SCC) or self-consolidation concrete is a high-fluidity concrete (HFC).Self-compacting means it can be easily placed and consolidated by its own gravity in a formwork,even with highly congested reinf...

  • Page 312

    6.5Self-Compacting Concrete297SCC project proved that SCC was practical for application using a variety of local materials,and that the expected benefits were obtainable in real construction practice. The working groupon SCC set up under RILEM TCI45-WSM was converted to a new RILEM workgroup (TC...

  • Page 313

    298Chapter 6Advanced Cementitious Compositesalso measures the maximum nominal diameter that the SCC can reach after lifting the slumpcone without limiting the time. Usually, the SCC should be able to reach a nominal diameterof 600 mm. And (4) the flow test can also provide some information on th...

  • Page 314

    6.5Self-Compacting Concrete29975 mm150 mm75 mm500 mm425 mmFigure 6-44Schematic diagram of a V-funnelTable 6-18Recommended values of V-funnel timeSourceRange (sec)European Federation of National Trade Associations (2002)6– 12Precast/Prestressed Concrete Institute (2003)6– 10Self-compacting Con...

  • Page 315

    300Chapter 6Advanced Cementitious CompositesClearspacing360 mm300 mm30 mmφ12 mm100 mmFigure 6-45Schematic diagram of a J-ringDaczko, 2003; Khayat et al., 2004). Ideally, the clear spacing between the steel bars of the J-ringshould be the same as the minimum clearance of the steel reinforcing bar...

  • Page 316

    6.5Self-Compacting Concrete301of the passability of SCC. Regarding the flow reduction, 50 mm is an index accepted by allresearchers and guidelines.6.5.2.4 U-box testThe U-box test was originally developed in Japan (Hayakawa et al., 1993). In this test, a spe-cially designed U-shaped tube, compri...

  • Page 317

    302Chapter 6Advanced Cementitious Composites(RILEM, 2002; Sonebi, 2004; Self-Compacting Concrete European Project Group, 2005; Testing-SCC Project Group, 2005a), but the most commonly used version has a length of 700 mm. Asliding gate is inserted at the bottom of the vertical compartment. A numbe...

  • Page 318

    6.5Self-Compacting Concrete30315 minutes, 2 liters (about 4.8 kg) of the top portion of the concrete sample is poured gently ontothe sieve at a height of 500 mm. The fine portion of the concrete without sufficient adhesion tothe aggregate particles will drip through the openings of the sieve to...

  • Page 319

    304Chapter 6Advanced Cementitious Composites36124824Time (h)Electrical resistivity (Ohm·m)1551020257260NCPtPSCC-0Figure 6-47The electrical resistivity of SCC and normal concreteTable 6-22Mix proportions of concrete per cubic meter (kg/m3)Viscosity Modifying AgentNameWaterCementFly AshSandCoarse ...

  • Page 320

    6.5Self-Compacting Concrete30504Electrical resistivity (Ohm·m)4681012812Time (h)PtpSCC-1SCC-2SCC-3SCC-0162024Figure 6-48The electrical resistivity curves of SCC with various VMAs up to 24 hoursof the paste at lower water– powder ratios. Usually, the powder content is increased up to600 kg/m3 o...

  • Page 321

    306Chapter 6Advanced Cementitious CompositesWaterCementFine aggregateCoarse aggregateWaterCementFine aggregateCoarse aggregateConventional concrete mixtureSelf-compacting concrete mixtureFigure 6-49Mix proportions of conventional and self-compacting concrete mixturesA low aggregate content in the...

  • Page 322

    6.5Self-Compacting Concrete3076.5.3.2 Viscosity-modifying agent type SCCIn a VMA type of SCC, to satisfy the rheological requirements of SCC, superplasticizer and—VMAs are incorporated into SCC mixtures. The incorporation of superplasticizers can largelydecrease the SCC yield stress with a limi...

  • Page 323

    308Chapter 6Advanced Cementitious Compositessite is a lack of knowledge about the lateral pressure generated by SCC on the formwork (Shahet al., 2009).Formwork pressure depends on the fluidity and cohesion of the SCC, rate of vertical rise,and the method of placing (from the top or from the bott...

  • Page 324

    6.5Self-Compacting Concrete309Table 6-23The mix proportion of a C60 self-compacting concrete (kg/m3)CementFly AshSandCrushed LimestoneWaterSuperplasticizer3602408008401757.1Table 6-24Properties of the fresh and hardened C60 concreteFresh Concrete After 1 Hour of CastingCompressive Strength (MPa)A...

  • Page 325

    310Chapter 6Advanced Cementitious Composites6.6 ENGINEERED CEMENTITIOUS COMPOSITEEngineered cementitious composites (ECC) are special types of random short-fiber-reinforced,cement-based composites. The representative characteristic of ECC is its excellent ductility andtoughness. The early work a...

  • Page 326

    6.6Engineered Cementitious Composite311and is referred to as the complementary energy. Since the maximum value (area B) of thiscomplementary energy Jb occurs whenσ increases to the peak stressσ0, andδ to the crackopeningδ0, it implies an upper limit on the matrix toughness as a condition for ...

  • Page 327

    312Chapter 6Advanced Cementitious Composites6.7 TUBE-REINFORCED CONCRETESteel has the advantages of high strength and excellent ductility. When steel is used as a structuralmember, especially a compressive member, the cross section is usually small and hence stiffnessis limited. Concrete has adva...

  • Page 328

    6.7Tube-Reinforced Concrete313Figure 6-53Application of CFST as a short axially loaded column in Tianjin Station,China (Photo provided by Linhai Han)moment frame connections, since they transfer relatively large axial forces to the column, whichmust be distributed between the steel and concrete. ...

  • Page 329

    314Chapter 6Advanced Cementitious Composites(a)(b)Figure 6-54(a) Guangzhou TV Tower under construction and (b) site view of finishedtower in China (Photo provided by Linhai Han)Figure 6-55Wushan CFST arch bridge, Chongqing China

  • Page 330

    6.7Tube-Reinforced Concrete315(a) Cross sections of hollow CFST(b) Cross sections of fibrous-composite-tube (Outside) reinforced concrete with steel insideFigure 6-56Typical cross sections of hollow CFST or composite concrete-filledtubular memberBucklingoutwardBucklinginwardBuckling inwardBuckli...

  • Page 331

    316Chapter 6Advanced Cementitious CompositesGirderInternal hollowCFSTInsidesteel tubeConcreteOutsidesteel tubeFoundationFigure 6-58Compositetypeof tall bridgepiera steel tube having an inner surface and a concrete core cast within the steel tube. Under normalconditions, the concrete core is bonde...

  • Page 332

    6.11Discussion Topics3176.9 STRUCTURAL LIGHTWEIGHT CONCRETEStructual lightweight concrete is defined as a concrete having compressive strength in excess17 MPa with a bulk density less than 1950 kg/m3. To make lightweight concrete, light weightaggregate has to be used. Nowadays, structural lightw...

  • Page 333

    318Chapter 6Advanced Cementitious CompositesFigure 6-59Heavyweight concrete for soundproofing15202530354045500100200300400500Frequency/HzTransmission loss/dBConcreteGypsum+foamGypsum+airHeavyweightconcreteFigure 6-60Experimental results of sound shielding with different constructionmaterialsWhat...

  • Page 334

    Problems319Can you think of a case suitable for the application of fiber-reinforced concrete?Can you design a fiber-reinforced concrete with strain-hardening behavior?How can you improve concrete strength using micro engineering?Suppose that you are a civil engineer. Which materials would you r...

  • Page 335

    320Chapter 6Advanced Cementitious CompositesREFERENCESACI (1997) 503.4-92 Standard specification for repairing concrete with epoxy mortars, American ConcreteInstitute.ACI (1998) 503R-93 (Reapproved 1998) Use of epoxy compounds with concrete, American ConcreteInstitute.ACI Committee 237 (2007) Se...

  • Page 336

    References321Daczko, J.A. (2003) “A comparison of passing ability test methods for self-consolidating concrete,” Pro-ceedings of the 3rd international RILEM symposium on self-compacting concrete, RILEM PublicationSARL, pp. 335– 344.Daczko, J. and Kurtz, M. (2001) “Development of high volu...

  • Page 337

    322Chapter 6Advanced Cementitious CompositesHwang, S.D., Khayat, K.H., and Bonneau, O. (2006) “Performance-based specifications of self-consolidatingconcrete used in structural applications,” ACI Materials Journal , 103(2), 121– 129.Isenberg, J.E. and Vanderhoff, J.W. (1974) “Hypothesis ...

  • Page 338

    References323Li, V.C., (1998) “Engineered cementitious composites– tailored composites through micromechanical mod-eling,” Fiber reinforced concrete: present and the future, Eds. N. Banthia et al, CSCE, Montreal, pp.64– 97.Li, V. C. and Leung, C.K.Y. (1992) “Steady state and multiple cr...

  • Page 339

    324Chapter 6Advanced Cementitious CompositesMori, A. and Baba, A. (1994) “A method for predicting the operating characteristics curing extrusionmolding process for cementitious materials.” In:Brandt, A.M., Li, V.C., and Marshall, I.H., eds.,Proceedings of the international symposium on brittl...

  • Page 340

    References325Sonebi, M. (2004) “Applications of statistical models in proportioning medium-strength self-consolidatingconcrete,” ACI Materials Journal , 101(5), 339– 346.Sonebi, M. Grunewald, S. and Walraven, J. (2007) “Filling ability and passing ability of self-consolidatingconcrete,”...

  • Page 341

    CHAPTER7CONCRETE FRACTURE MECHANICS7.1INTRODUCTIONAccording to the tensile stress– strain curve, materials can be divided into brittle materials,quasi-brittle materials and ductile materials (see Figure 1-10). As shown in Figure 1-10a, brittlematerials break suddenly when the stress reaches max...

  • Page 342

    7.1Introduction327b0b0σσFigure 7-1Lattice structure under stressingshown in Figure 7-1. Furthermore, if we assume that only adjacent neighbors interact, we havethe situation shown in Figure 7-2. Two ions will attract each other when b> b0 and repel eachother when b< b0.Let F be the force ...

  • Page 343

    328Chapter 7Concrete Fracture MechanicsbFb0bFFigure 7-2Force acting on two neighboring ionsLinear elastic fracture mechanics (LEFM) theory was developed in 1920 with Griffith(1921) as the founder. His original interest was on the effect of surface treatment on the strengthof solids. It had been ...

  • Page 344

    7.1Introduction329science concerned itself with the fracture processes on the scale of atoms and dislocations tothat of impurities and grains and provided an understanding on the origin and driving force ofmicrocracks. Large-scale engineering mechanics provided analysis methods for stress and def...

  • Page 345

    330Chapter 7Concrete Fracture Mechanicsproposed a crack band model based on the concept of strain softening to explain the fractureprocess of concrete. Wecharatana and Shah (1982, 1983) used a compliance based model tocalculate the length of the fracture process zone, which was represented by tra...

  • Page 346

    7.2Linear Elastic Fracture Mechanics331the edge of the hole. Theσmax is much larger than the normal stress,σN. This phenomenonis called a stress concentration. The stress concentration factor, Kt, for the given loadingcondition in Figure 7-3, can be expressed asKt=σmaxσN= 1+2ac(7-7)where a an...

  • Page 347

    332Chapter 7Concrete Fracture Mechanicsbased on the concentration factor is not valid for a structure with a sharp crack; therefore,fracture mechanics should be introduced.(b) Stress intensity factor : In fracture mechanics, cracks are classified into mode I (openingmode), mode II (shearing mode...

  • Page 348

    7.2Linear Elastic Fracture Mechanics333value but Kt approaches infinity. The value of KI accounts for the singularity of the stress fieldin the crack tip, and is a function of load, specimen geometry and size, boundary condition, andcrack length.The fundamental postulate of linear elastic fract...

  • Page 349

    334Chapter 7Concrete Fracture Mechanicsthe displacement extrapolation techniques exhibited some erratic characteristics and are highlysensitive to the nodal displacement distribution. In other words, fortuitously, more accuratedisplacements do not always give more accurate SIFs because of the int...

  • Page 350

    7.2Linear Elastic Fracture Mechanics335A reliable, highly accurate and easily implemented procedure to extract the SIFs shouldhave the following features: (1) The procedure should make full use of the COD data to increasethe accuracy of the results, and the information of COD fields should not b...

  • Page 351

    336Chapter 7Concrete Fracture MechanicsBPPFigure 7-6A specimen with an edge crack under loadingFor simplicity, body forces are neglected. The total potential energy in the structure can beexpressed as= U− F+ W(7-23)where U= U(a, ε) is the strain energy of the structure and a function of crack ...

  • Page 352

    7.3The Crack Tip Plastic Zone337For the condition of fixed displacement, we haveG=−P 22B∂C∂a(7-28)Define Gc= 1/B (dW /da) as the critical strain energy release rate of the materials; then G= Gcrepresents the condition for the equilibrium state of the structure during crack propagation. Si...

  • Page 353

    338Chapter 7Concrete Fracture Mechanicswithσy:σy=KI2π r ∗p= σys(7-31)and we haver ∗p =K 2I2πσ 2ys=σ 2a2σ 2ys(7-32)However, the size of the actual plastic zone must be larger than r ∗p because it will not satisfyequilibrium by just simply cutting off the stress area above the yield s...

  • Page 354

    7.3The Crack Tip Plastic Zone339A different approach to find the size of plastic zone was followed by Dugdale (1960).Dugdale assumed the length of plastic zone to be much greater than the thickness of the sheetand modeled the plastic zone as a yield strip ahead of the crack tip. Dugdale applied ...

  • Page 355

    340Chapter 7Concrete Fracture MechanicsThe integral result isKρ= 2paπarccossa(7-42)Applying this result to the Dugdale crack, the integral had to be taken from s= a to a+ ρ.Hence, a had to be substituted for s and a+ ρ for a, while p= σys.Kρ= 2σysa+ ρπarccosaa+ ρ(7-43)According to Dugda...

  • Page 356

    7.4Crack Tip Opening Displacement341CTOD2a2a+2rpCODFigure 7-11Sketch of crack opening displacementIt can be seen that if there is no crack propagation, when x= a, then CTOD= 0. When x= 0,COD reaches maximum,CODx=0 =4σEa(7-49)Since the stress is usually two or three orders of magnitude smaller th...

  • Page 357

    342Chapter 7Concrete Fracture Mechanics7.5 FRACTURE PROCESS IN CONCRETETo study fracture progress in concrete, uniaxial tension tests have been carried out with mon-itoring of the microcrack occurrence using the acoustic emission technique. The test setup isshown in Figure 7-12. As can be seen fr...

  • Page 358

    7.5Fracture Process in Concrete34301000200030004000Time (second)0.01.02.03.04.05.06.0Tensile stress (MPa)02004006008001000Accumulated event number020406080100Event rate (per minute) Tensile stress Accumulated event number Event rateFigure 7-13Tensile stress and accumulated acoustic events as func...

  • Page 359

    344Chapter 7Concrete Fracture Mechanics(a)(b)(c)(d)2101801501209060300020406080 100 020406080 100 020406080 100 020406080 100X-direction (mm)X-direction (mm)X-direction (mm)X-direction (mm)Y-direction (mm)Figure 7-14The distribution of microcracks that occurred during the loading stagebetween (a)...

  • Page 360

    7.5Fracture Process in Concrete345Centre holeDisplacementheld measurementPnotchP2LPP−1.0 −0.50.00.51.0−1.0 −0.5−1.0−1.5−2.0−2.5−3.0−4.0−3.5−1.0−1.5−2.0−2.5−3.0−4.0−3.50.00.51.0(a) Load = 1324 lbCrack length = 1.38 in.−1.0 −0.50.00.51.0−1.0 −0.5−1.0−...

  • Page 361

    346Chapter 7Concrete Fracture MechanicsDepth = 56 mmDepth = 28 mmDepth = 14 mm0.00.10.20.30.40.50.60.00.20.40.60.8Ratio of crack size to depthCritical stress intensity factor (MN/m3/2)Figure 7-17Dependency of the stress intensity factor on the crack size in concretelinear elastic fracture mechani...

  • Page 362

    7.6Nonlinear Fracture Mechanics for Concrete347σ(w)dxσ(w)xa0a∆awtInitial crackftApplied load, PFigure 7-18Modeling of cohesive stress for a quasi-brittle crackBy analoging Dugdale’s model, an effective inelastic crack or effective quasi-brittle crack ina concrete can be drawn. Figure 7-18 s...

  • Page 363

    348Chapter 7Concrete Fracture Mechanicsdissipation mechanism is represented by a nonzero stress intensity factor and the Dugdale-Barenblatt energy dissipation mechanism is represented by the traction term. It seems that itis proper to use these two energy dissipation mechanisms to describe the pr...

  • Page 364

    7.7Two-Parameter Fracture Model349LS = 4ba0 = b/3Ptba0CMODH0a0Figure 7-19Three-point bending test setup for the two-parameter modelCMOD*CCMODPOCuCiUnloadingat peak loadCMODσcσFigure 7-20Loading and unloading procedureCTOD =CTOD* + CTODPCMOD =CMOD* + CMODPInitianl crackσσFigure 7-21The schemat...

  • Page 365

    350Chapter 7Concrete Fracture MechanicsThe value of the critical crack tip opening displacement CTODc can then be determined basedon the obtained values of CMODec:CTODec = CMODecg3acb(7-62)In the above three equations, g1, g2 and g3 are geometrical functions for calculating KSIc,CMODec,and CTODec...

  • Page 366

    7.7Two-Parameter Fracture Model351such as concrete, the stable crack extension occurs before the critical fracture. Since CTODc isdefined at the tip of the initial crack, it may primarily account for the growth in size of the weakprocess zone.7.7.2 Determination of fracture parameters for the tw...

  • Page 367

    352Chapter 7Concrete Fracture Mechanicswhere Ci is the initial compliance calculated from the load– CMOD curve and g2(α0) isg2 (α0)= 0.76− 2.28α0+ 3.78α20 − 2.04α30 +0.66(1− α0)2(7-68)whereα0= (a0+ HO) / (b+ HO), in which HO is the height of the holding plates for the clipgage or L...

  • Page 368

    7.7Two-Parameter Fracture Model3537.7.3 Some applications of the two-parameter model(a) Material length, Q : When the values of K SIc and CTODec are known for a concrete, somematerial characteristic properties can be identified. For example, a material length, Q , canbe defined asQ=E× CTODcK s...

  • Page 369

    354Chapter 7Concrete Fracture MechanicsBeam Death (m)000.40.81.21.62246810Critical Nominal Stress (MPa)ac = 0ac = 10 mmFigure 7-24Critical nominal stress predicted by the two-parameter modelIf the values of KIc and ac are determined from the two-parameter model, the size effecton the tensile nomi...

  • Page 370

    7.8Size Effect Model3550.001.001.101.201.301.401.500.902.004.006.008.0010.00bQMORf1MORf1CEB·FIP (Q = 8)= 0.6 +0.4b(m)<1b4bPQ = (E·CTODc)2Ksk(Ksk)2f1 = 1.4705 E·CTODcTheoretical PredictionFigure 7-25Effect of beam depth on MOR by the two-parameter fracture model andCEB-FIP model code02468101...

  • Page 371

    356Chapter 7Concrete Fracture Mechanicswhere A1 is a constant, D the characteristic dimension of the structure, and s the size coefficient,which is a measure of the size effect for a structure with different geometries and loading patterns.The so-called size effect law was developed by Bazant (1...

  • Page 372

    7.8Size Effect Model357WcmWcpWcmdpdpapapdmdmamamWcp==Figure 7-27Two geometrically similar specimens with a crackenergy released at failure, Wtotal, depends on fracture length, fracture bandwidth, or area of thefracture zone; (b) cracks at failure are similar (i.e., following geometric similarity)...

  • Page 373

    358Chapter 7Concrete Fracture MechanicsIt may be assumed that the geometrical function g(α1, α2) is positive, i.e., g(α1, α2) > 0. Thenwe can expand g(α1, α2) with respect toα2,at α2= 0:g(α1, α2)= g(α1,0)+ g(α1,0)α2+ ···(7-91)By substituting equation 7-91 into 7-90, we getσN=2...

  • Page 374

    7.8Size Effect Model359Log(D0)Log(σN)1Nonlinear fracturemechanicsStrengthcriterionLog(Bft)Linear elastic fracture mechanicscriterionLog(D)2Figure 7-29The size effect law, together with the strength criterion and the LEFMcriterionThe brittleness number,β, depends not only on the material fractur...

  • Page 375

    360Chapter 7Concrete Fracture MechanicsNote thatlimD→∞DD+ D0= 1(7-102)andlimD→∞gacD= ga0D(7-103)These two results fromac are negligible compared to the initial crack length when the structuresize approaches infinity. Thus, we haveGf=B 2f 2t D0Ec2nga0D(7-104)This equation relates the mate...

  • Page 376

    7.8Size Effect Model361Inversing the equation gives1c−2nσ 2N=cfga0D+ ga0DDEGf=cfga0DEGf+ga0DDEGf(7-110)If we take 1/c2n σ 2Nas y, D as x , and cfg (a0/D) /EGf and g(a0/D) /EGf as constants, we havea linear equation.7.8.2 Method of Bazant et al. to determine Gf and cf(a) Specimens and test pro...

  • Page 377

    362Chapter 7Concrete Fracture Mechanics(b) Test results and calculations: First, the corrected maximum loads, P 0jshould be obtainedby taking the weight of the specimen into account:P0j = Pj+Sj2LJWj(7-111)where Pj is the maximum load, Sj the span, Lj the total length, and Wj the weight of thespec...

  • Page 378

    7.8Size Effect Model363For S/b= 8,g1a0b= 1.11− 1.552a0b+ 7.71a0b2− 13.55a0b3+ 14.25a0b4(7-121)Linear interpolation may be used to obtain g1(α0) for the other values of S /b.The values of the material fracture energy Gf can be determined fromGf=g(α0)EA(7-122)The critical value of the fractur...

  • Page 379

    364Chapter 7Concrete Fracture Mechanics7.9 THE FICTITIOUS MODEL BY HILLERBORG7.9.1 The modelThe basic premise of the present analysis is that the best available fracture model for concreteis the cohesive crack of the fictitious crack model, pioneered and generalized by Hillerborget al. (1976). H...

  • Page 380

    7.9The Fictitious Model by Hillerborg365numerical analysis. The expression ofσ= σ(ft, w) can be linear, for example,σ= ft(1− w/wc)or exponential, for example,σ= fte−A(w/wc).The fictitious crack model requires three parameters: ft, GF, and the shape ofσ(w). Whenthe shape ofσ(w) is given...

  • Page 381

    366Chapter 7Concrete Fracture Mechanicswcftww1σ1σFigure 7-32Bilinear curve modeling of the closing pressureft0.3 ftw1w2wcwσFigure 7-33Trilinear curve modeling of the closing pressurewcftwσσ(w) = fteAwBFigure 7-34Exponential curve modeling of the closing pressurewc is found using this approac...

  • Page 382

    7.9The Fictitious Model by Hillerborg367wc0.4 ftwσσ(w) = 0.4 ft(1 − w/wc)1.5Figure 7-35Power curve modeling of the closing pressure7.9.3 Test method to determine GFA three-point bend beam is recommended to be used. The size of the beam depends on themaximum size of aggregate. The notch depth ...

  • Page 383

    368Chapter 7Concrete Fracture Mechanicsa0a0SLtbPPPwPaW0W1W2bδ0δδFigure 7-36Experimental setup and load-displacement curvegFigure 7-37Lateral loading setupBy noting the influence of gravity in these two loading patterns, which are different fromthe downward loading pattern, we can readily writ...

  • Page 384

    7.10R-Curve Method for Quasi-Brittle Materials369gFigure 7-38Upward loading setupthe GF values may partially be due to the unwanted energy absorption outside the fracture zone.The value of GF was found to be 90 N/m from some experiment results.7.10 R-CURVE METHOD FOR QUASI-BRITTLE MATERIALS7.10.1...

  • Page 385

    370Chapter 7Concrete Fracture Mechanicsrising function of crack extension. When the value of Gq increases, due to the increase of appliedload, the value of R also increases due to the incremental of crack length. Therefore, Gq= Rcan only serve as a necessary condition for failure. A crack may be ...

  • Page 386

    7.10R-Curve Method for Quasi-Brittle Materials371Leta0+ ac= αa0(7-147)Then we havea0=acα− 1(7-148)and Equation 7-146 becomes(α− 1)Gi= α( ac)dGdai(7-149)orαα− 1( ac)dGd( ac)− G= 0(7-150)This is a typical form of the Euler equation and its solution can be obtained by the variableexcha...

  • Page 387

    372Chapter 7Concrete Fracture MechanicsFailure criteria:Gq = R∂a∂R∂a∂GqGq-curveGq, Raa0 acR-curvePerfectly brittlematerials=Figure 7-40Schematic of the R-curveUsing Gq= 0at a= 0 results in the following equation:Gqc =−∞n=11n!d n Gqdan(a− ac)n(7-153)For materials with a precritical s...

  • Page 388

    7.10R-Curve Method for Quasi-Brittle Materials373withd0=α− 1α(7-159)This R-curve can be used for materials with a small crack extension, such as metals. Forquasi-brittle materials, more terms have to be considered. Ouyang et al. (1991) developed anexpression for n= 2 as follows:12αα− 12c2...

  • Page 389

    374Chapter 7Concrete Fracture Mechanicswhere f1 is a geometrical factor of infinitely sized structure for the stress intensity factor. Forthe tension mode specimen its value is 1.0 for center crack specimen, and 1.12 for single edgecrack tensile specimen.Substituting Equations 7-164 and 7-167 in...

  • Page 390

    Problems375Do you think fracture-based design will soon become dominant for civil engineers? Why?For shear and flexural design of reinforced concrete structures, which one is more suitable touse in fracture mechanics as a design guideline?PROBLEMS1. A type of steel has a KII value of 66 MPa√m ...

  • Page 391

    376Chapter 7Concrete Fracture Mechanicsfrom the equation of CMODc = (4σca0/E )g2 (α0),where t is the beam thickness and b the beam height,referring to Figure P7-4 (self-weight of the beam can be ignored).CiCv02.55.07.510.012.515.017.520.002505007501000Lood,P (N)Crack mouth opening displacement,...

  • Page 392

    Problems377KI=2p√π a(a− a2− b2)rbbbaaσσFigure P7-5bA round crack under distributed loading6. For n= 2, derive the solution of the R-curve (with detailed procedures) given byR+∞n= 11n!d n Rdcnαα− 1n(−c)n = 0(7-173)7. Consider a semi-infinite crack in a thin plate as shown in Figu...

  • Page 393

    378Chapter 7Concrete Fracture Mechanics8. Using the configuration shown in Figure P7-8, show that for plane stress, we have the following (Hint :The relationship between K and G for mode I can be applied to mode II):KII=Pt√2h(7-175)hatFigure P7-8A thin plate with an edge crack under plane stre...

  • Page 394

    References379REFERENCESBazant, Z.P. (1984) “Size effect in blunt fracture: concrete, rock, metal,” Journal of Engineering Mechanics,ASEC , 110(4), 518– 535.Bazant, Z. P. and Kazemi, M. T. (1990) “Determination of fracture energy, process zone length andbrittleness number from size effect,...

  • Page 395

    380Chapter 7Concrete Fracture MechanicsLeicester, R.H. (1973) Effect of size on the strength of structures, Report paper No. 71, CSIRO Forest Prod-ucts Laboratory, Division of Building Research Technology, Commonwealth Scientific and IndustrialResearch Organization, Australia.Li F. and Li, Z. (2...

  • Page 396

    CHAPTER8NONDESTRUCTIVE TESTINGIN CONCRETE ENGINEERING8.1INTRODUCTION8.1.1 General descriptionThere are two kinds of tests, destructive and nondestructive, that can be utilized to assessthe properties of concrete material or structures. Destructive testing obtains the materials orstructural proper...

  • Page 397

    382Chapter 8Nondestructive Testing in Concrete Engineeringand infrastructures by estimating the properties and performance of materials and structures.NDT-CE can localize and measure the defects or damage inside a structure for repair or removalpurposes. It also can be used to find the position ...

  • Page 398

    8.1Introduction383Detection possibilityDefect sizeDetection limitFigure 8-1No clear cutoff in detection resolutionor crack is detected, it can be allowed to remain if its size is less than a critical value. Moreover,tolerance can be applied to the inspection interval on different concrete structu...

  • Page 399

    384Chapter 8Nondestructive Testing in Concrete Engineeringbut the signal processing scheme sometimes plays a significant role in the data interpretationprocedure. Nowadays, signal processing (SP) has become an essential and necessary procedurein NDT measurements. Signal processing can be analog ...

  • Page 400

    8.1Introduction385the test specimen. The signals gathered reflect the nature of the test object. Building dynamicsis an example. In building dynamics, the natural frequency or eigenfrequency of a structure(a building, a bridge, etc.) is excited by a random load and measured. The mode shapes cana...

  • Page 401

    386Chapter 8Nondestructive Testing in Concrete Engineeringa concrete structure has gone through a fire, the residual strength of the damaged concretehas to be determined in order to make decisions for renovation work. The true steel yieldstress of a concrete structure during service and after a ...

  • Page 402

    8.1Introduction387Mechanical waves are not harmful to the human body, which is an important advantage overradiation.The basic theory involved in MWT methods is elastic wave generation, propagation, andreception. Wave propagation involves reflection, transmission, and scattering, as well as diffr...

  • Page 403

    388Chapter 8Nondestructive Testing in Concrete Engineering(b) Electromagnetic wave technique (EMT): Among NDT methods in concrete engineering,the electromagnetic wave technique is one of the most powerful, as most nonmetal materials areamenable to electromagnetic waves. This kind of technique use...

  • Page 404

    8.1Introduction389T-girders and metallic anchors in prefabricated three-layer concrete elements, the location ofplastic and metallic leads, measurement of cover thickness of concrete, and moisture measure-ment of concrete. The artificial birefringence properties can be found for ceramics and cem...

  • Page 405

    390Chapter 8Nondestructive Testing in Concrete EngineeringReferenceelement RRTest elementRTR1R2Figure 8-2Basic circuit for the electrical resistance probe techniqueof associated sampling techniques required for locating the probes in a large structure subject tolocalized corrosion.(e) Magnetic me...

  • Page 406

    8.1Introduction391magnetization characteristics, location, and geometry of the metal. The inductance of the coilcan be used to measure coil-to-place distance if the relationship between mutual inductanceand the coil-to-place distance is known. The magnetic induction theory has resulted in thedeve...

  • Page 407

    392Chapter 8Nondestructive Testing in Concrete EngineeringThe analysis is extended into the change of the stiffness of the structure to access the damagedegree of the building under inspection.Building dynamics techniques are widely used in structural engineering. Simple methodsare useful for ass...

  • Page 408

    8.1Introduction393frequency and is referred to as the relaxation time. The specific damping capacity and associateddynamic response of the material are characterized by the damping coefficient, which can beexpressed byα=1NlnA0An(8-2)whereα is the damping ratio; A0 the vibration amplitude of t...

  • Page 409

    394Chapter 8Nondestructive Testing in Concrete Engineeringconcrete, some energy is absorbed, some energy passes through, and a significant amount isscattered by collisions with electrons in the concrete. So when employingγ -rays in examiningconcrete, there are basically two modes of transmissio...

  • Page 410

    8.2Review of Wave Theory for a 1D Case3958.2.1 Derivation of the 1D wave equationFor an elastic solid, that is homogeneous, isotropic, and linear elastic, we have the followingequations:By Hooke’s lawεxx=1Eσxx− v σyy+ σzzεyy=1Eσyy− v (σxx+ σzz )(8-5a)εzz=1Eσzz− v σyy+ σxxεxy=...

  • Page 411

    396Chapter 8Nondestructive Testing in Concrete EngineeringFor the stress expressions, we haveσxx= 0σyy=ν1− νσxx(8-10)σzz=ν1− νσxxSubstituting into Equation 8-5, we haveεxx=1Eσxx− ν σyy+ σzz=1E(1+ ν)(1− 2ν)1− νσxx(8-11)Or in term of stress, we haveσxx= E1− ν(1+ ν)(...

  • Page 412

    8.2Review of Wave Theory for a 1D Case397For the one-dimensional stress case, we haveC2L =Eρ(8-17)8.2.2 Solution for a 1D wave equation8.2.2.1 Longitudinal wave caseThe wave equation for the longitudinal case is∂2U∂x 2 =1C 2L∂2U∂t 2(8-15)where CL represents the longitudinal wave velocity...

  • Page 413

    398Chapter 8Nondestructive Testing in Concrete EngineeringThe second integral is made with respect toα, givingU= f(α)+ g(β)(8-27)orU= ft−xCL+ gt+xCL(8-28)This is the so called D’Alembert solution. The term f(t− x /CL) represents a pulse propa-gated with the velocity of CL in the positive...

  • Page 414

    8.2Review of Wave Theory for a 1D Case399Note thatC2L =Eρfor plane stress(8-18)C2L =λ+ 2µρfor plane strain(8-19)Thus, for the plane strain case, we haveC 2LC 2T=2(1− v)1− 2v(8-35)For the plane stress case, we haveC 2LC 2T= 2(1+ v)(8-36)The solution of the S-wave equations can be obtained ...

  • Page 415

    400Chapter 8Nondestructive Testing in Concrete Engineeringand for f= 0, we haveσxx= ρCL∂U∂t(8-42)This means that the stress can be expressed as a function of the rate of wave propagation anddifferent directions give different signs. The termρCL is also called acoustic impedance.8.2.2.4 Spe...

  • Page 416

    8.2Review of Wave Theory for a 1D Case401The physical meaning of the wavelength (denoted asλ) is the distance between two sequentialcrests (or troughs). This generally is measured in meters; it is also commonly measured innanometers for the optical part of the electromagnetic spectrum.The variab...

  • Page 417

    402Chapter 8Nondestructive Testing in Concrete EngineeringWe can derive the following relationships:T=2πωf=1T=ω2πω= 2π fk=2π fCL(8-54)Example of the variable separation methodSolve the following 1D wave equation using the variable separation method.Uxx=1C 2LUttU|x=0 = 0U|x=l = 0Solution:Le...

  • Page 418

    8.3Reflected and Transmitted Waves403The second case isλ= 0:X(x )= C1x+ C2From boundary conditions X (0)= 0 and X (l)= 0,C2= 0C1l+ C2= 0Again, X(x )≡ 0 (No meaning)The third case isλ > 0:X(x )= C1 cos√λx+ C2 sin√λxFrom boundary conditions X (0)= 0 and X (l)= 0,C1= 0C2 sin√λl= 0Si...

  • Page 419

    404Chapter 8Nondestructive Testing in Concrete EngineeringhALCx− aCLta −−gx− aCLCLta +−x= ap, CLpA, CLAfCLtx−Figure 8-7One-dimensional wave propagation at an interface between two mediumsThe reflection and transmission behavior of the wave front at an interface plays an importantrole...

  • Page 420

    8.3Reflected and Transmitted Waves405where AR is the displacement amplitude of reflected wave; AI the displacement amplitude ofincident wave; and AT the displacement amplitude of transmitted wave; andσR=ρAC ALρCL− 1ρAC ALρCL+ 1σI=z− 1z+ 1σI= RσIσT=2ρAC ALρAC AL + ρCLσI=2zz+ 1σ...

  • Page 421

    406Chapter 8Nondestructive Testing in Concrete EngineeringWhen the wave fronts propagate on the boundary between two materials with differentproperties, with an angle not normal to the interface, the reflection and transmission will dependon the angle. Letθ be the wave incidence angle. The re...

  • Page 422

    8.5Main Commonly Used NDT-CE Techniques4078.5 MAIN COMMONLY USED NDT-CE TECHNIQUES8.5.1 Ultrasonic technique8.5.1.1 Principle of ultrasoundAs mentioned earlier, the ultrasonic technique (UT) is based on time-varying deformations orvibrations in materials, which are generally referred to as acoust...

  • Page 423

    408Chapter 8Nondestructive Testing in Concrete EngineeringAsymmetricSymmetricFigure 8-9Asymmetric and symmetric Lamb wavesWith Lamb waves, a number of modes of particle vibration are possible, but the two mostcommon are symmetrical and asymmetrical, as shown in Figure 8-9. The complex motion of t...

  • Page 424

    8.5Main Commonly Used NDT-CE Techniques4098.5.1.2 Technical features and advancesWhen applying UT to concrete or other cement-based materials and structures, some difficultiescan be encountered due to the material features. First, concrete is an inhomogeneous, porous,multiscale, and heterogeneou...

  • Page 425

    410Chapter 8Nondestructive Testing in Concrete Engineeringwas developed. A pair of powerful 40-kHz transducers produce an ultrasound beam to punchthrough and test brick or concrete samples without contact (APCNDT, 1998). The powerfultransducers matched the high-performance electrical circuits, wh...

  • Page 426

    8.5Main Commonly Used NDT-CE Techniques411Power supplyPulser circuitMaker circuit(optional)ClockSweep circuitReceivercircuitEcho intensityOscilloscope screenFlaw Test pieceSound beamSearch unitInitial pulse Flaw echoSweep traceBack reflectionFigure 8-10Sketch of the A-scan techniquePower supplyPu...

  • Page 427

    412Chapter 8Nondestructive Testing in Concrete Engineeringthe echoes inside the window are displayed in a bright point format, of which the brightness isproportion to the amplitude of the echo. The co-ordinates of the point displayed are just those ofthe source. Thus, a lateral cross-sectional pl...

  • Page 428

    8.5Main Commonly Used NDT-CE Techniques413transducer is placed on the top surface of a steel plate in contact with fresh concrete. The principleof the shear wave reflection measurement consists of monitoring the reflection coefficient of theultrasonic waves at an interface formed between the s...

  • Page 429

    414Chapter 8Nondestructive Testing in Concrete EngineeringInitial setting time (hours)Time of point A (hours)0246103546728AcceleratorSilicaPlainSuperplasticizerRetarderFigure 8-15Relationship between setting time and reflection lossCompressive strength (MPa)Reflection loss (dB)0102030502134040R2...

  • Page 430

    8.5Main Commonly Used NDT-CE Techniques415Figure 8-17A typical apparatus for using the longitudinal transmission methodVelocity (×1,000 m/sec)Age of concrete (hours)01235103020405004Reference16 ml/kg8 ml/kg25 ml/kgFigure 8-18A representative plot of wave velocity versus timeA typical plot of the...

  • Page 431

    416Chapter 8Nondestructive Testing in Concrete EngineeringThis embedded ultrasonic system has many advantages. First, it has good coupling betweenthe transducer and the matrix. Second, the method is very effective for hydration measurementof large-scale or underground concrete structures. Last, b...

  • Page 432

    8.5Main Commonly Used NDT-CE Techniques417Figure 8-20Placement of the transducers before castingTo measure the hydration process of fresh cement-based materials, the transducers shouldbe fixed in a predetermined position in a formwork before the casting of fresh concrete or othercement-based mat...

  • Page 433

    418Chapter 8Nondestructive Testing in Concrete EngineeringVelocity (×1,000 m/sec)Time (hours)11.522.53.51040206070035030Stage 2Stage 3Stage 4Stage 1Figure 8-22Development of the acoustic velocity in fresh concreteof the received signal. A threshold is preset based on the noise level. The time wh...

  • Page 434

    8.5Main Commonly Used NDT-CE Techniques419Wave length (mm) Time (hours)020406014020406080010012080Figure 8-23The calculated values of wavelengthDynamic modulus, E (GPa)Time (hours)05101520204060800Figure 8-24The calculated values of a dynamic Young’s modulusthe same period. The dynamic modulus ...

  • Page 435

    420Chapter 8Nondestructive Testing in Concrete EngineeringAE sources may also include the local stress distributions associated with chemical action, suchas alkali –aggregate reaction and corrosion of steel inside concrete. The AE signals carry thesource information and follow the elastic wave ...

  • Page 436

    8.5Main Commonly Used NDT-CE Techniques421to adding channels requires, great effort due to the increasing interaction among channels andthe fast expanding data and cost of equipment.The early AE testing instruments used analogue electrical devices. The ability to captureinstantaneous AE events an...

  • Page 437

    422Chapter 8Nondestructive Testing in Concrete Engineeringextensive series of investigations has been carried out by Maji and Shah (1988), Li and Shah(1994), Maji et al. (1990), Ouyang et al. (1991), and Landis et al. (1993). In these tests, concrete,mortar, and low-volume-fraction FRC specimens ...

  • Page 438

    8.5Main Commonly Used NDT-CE Techniques423the surface displacement. Preamplifiers are normally necessary because the outputs from thetransducers are usually low. The pre-amplifiers have two functions. One is to amplify the signalreceived by the AE transducers, usually using two magnification s...

  • Page 439

    424Chapter 8Nondestructive Testing in Concrete Engineeringspecific transducer located at a specific position. It can be seen from the figure that the first arrivaltime of the wave is different for different signals because the distances from the transducer tothe source of AE are different. Th...

  • Page 440

    8.5Main Commonly Used NDT-CE Techniques425It should be pointed out that solving Equations 8-71 through 8-73 together will provide not onlythe source location but also the wave velocity.The method is easy to expand to a 3D case. In this case, Equation 8-68 becomese1i= (x− x1)2+ (y− y1)2+ (z−...

  • Page 441

    426Chapter 8Nondestructive Testing in Concrete EngineeringAs an update, the Physical Acoustics Company (PAC) has developed software, PAC-PARS,using an artificial neural network (ANN) analysis system to characterize AE signals in a moreadvanced way. It uses twelve basic parameters in an AE signal...

  • Page 442

    8.5Main Commonly Used NDT-CE Techniques427Ch1Trigger signalidentifierThe LeCroy dataacquisition system6103Trigger6128Fan-outTR8828Digitizer8901AGPIBData analysisand storagePostanalysisPreamplifiers andband pass filtersCh2Ch3Ch4Ch5Figure 8-27Experimental setup for studying crack occurrenceThe acou...

  • Page 443

    428Chapter 8Nondestructive Testing in Concrete EngineeringA plain concrete specimen was tested in direct tension and monitored by AE measurementin mean time. Figure 7-31 (see Chapter 7) shows its deformation– time curves. It can be seenfrom the figure that the deformations in the specimen vary...

  • Page 444

    8.5Main Commonly Used NDT-CE Techniques429observed in the figure for regime (c), which corresponds to a stress level from 0.8ft to ft.Amajor crack has developed from the localization zone and is propagated across the width of thespecimen. The phenomenon agrees with the findings of Li and Shah (...

  • Page 445

    430Chapter 8Nondestructive Testing in Concrete EngineeringConcrete3% NaCl electrolytePlexiglas poolResistorRebarsTransducerPreamplifierAE systemFigure 8-30Experimental setup for a corrosion test of reinforcementFor steel, the shear modulus is about 81 GPa and the Kolosou constant is around 2. The...

  • Page 446

    8.5Main Commonly Used NDT-CE Techniques431AE event numberTime (Days)103020500Accumulated event number2005000250200150100500Current (mA)10030040040Galvanic currentFigure 8-31Comparison of the accumulated number of AE signals with galvaniccurrentxCorrosion spotTransducerRebarLFigure 8-32Measurement...

  • Page 447

    432Chapter 8Nondestructive Testing in Concrete EngineeringLocation along the rebar (in)51510200Number of AE events401200206080100Figure 8-33Calculated source locations of corrosionFigure 8-34The actual corrosion conditions of the reinforcementfrom carbonation attack to the concrete surface beneat...

  • Page 448

    8.5Main Commonly Used NDT-CE Techniques433LVDT_1LVDT_2PCeramic tileConcrete cubeSteel plateRigid supportL-shapesteel plateFigure 8-35Test setup for debonding detection of ceramic tiles on concreteComputerPrinterAE equipmentLeCroy 6103Pre-amplifierFigure 8-36The AE measurement system for debonding...

  • Page 449

    434Chapter 8Nondestructive Testing in Concrete Engineeringwas used to communicate with a personal computer via a GPIB board. The operation of theLeCroy system was controlled by a Physical Acoustics Catalyst program, which also stored thedigitized data on the computer’s hard disk. Three thousand...

  • Page 450

    8.5Main Commonly Used NDT-CE Techniques4350510152025303500.030.060.090.120.150.1800.030.060.090.120.150.18Displacement (mm)Load (kN)(a)05101520253035Displacement (mm)Load (kN)(b)20 cyclesFigure 8-38Acoustic emission under (a) cyclic and (b) monotonic loading of push-offtest048121600.030.060.090.1...

  • Page 451

    436Chapter 8Nondestructive Testing in Concrete Engineering0501001500306090120150Horizontal PositionVertical Position(a)0306090120150Horizontal Position050100150Vertical Position(c)0306090120150050100150Horizontal PositionDepth Position(b)0306090120150Horizontal Position050100150Depth Position(d)F...

  • Page 452

    8.5Main Commonly Used NDT-CE Techniques437and its use is actively growing (Brandes et al., 1998). A potentially important application ofquantitative AE is to monitor bridges and buildings to assess the degree of damage and servicelife. To know the history and the present situation, AE might be a ...

  • Page 453

    438Chapter 8Nondestructive Testing in Concrete Engineeringreceived by means of a microphone in air or a transducer on the specimen surface. IE works inthe acoustic and low ultrasonic frequency band. The received signals are analyzed mainly by thefast fourier transform (FFT). The multireflection ...

  • Page 454

    8.5Main Commonly Used NDT-CE Techniques439testing, in which the type of defects and shapes of structures are frequently met. ASTM C1383(2004) has proposed a standard test method based on the use of the impact-echo method tomeasure the thickness of plate-like concrete members. This method includes...

  • Page 455

    05101520254.7048.992Frequency (kHz)0510152025Frequency (kHz)MagnitudeW/C = 0.5, 8.0 Hours8.51216.384MagnitudeW/C = 0.5, 2.0-Day0510152025Frequency (kHz)0510152025Frequency (kHz)7.80214.912MagnitudeW/C = 0.5, 1.0-Day10.048 kHz19.296 kHzW/C = 0.5, 28.0-DayMagnitude0510152025Frequency (kHz)051015202...

  • Page 456

    8.5Main Commonly Used NDT-CE Techniques441A1=−8.6457LD2+ 24.443LD− 12.478(8-91)B1= 34.599LD2− 101.72LD+ 56.172(8-92)C1=−34.681LD2+ 105.98LD− 62.731(8-93)where L/D is length to diameter ratio.The calculated Poisson’s ratio from the experiments is plotted as a function of age inFigure 8...

  • Page 457

    442Chapter 8Nondestructive Testing in Concrete EngineeringAge (Days)1218300624Dynamic modulus of elasticity (GPa)010204030Plain concrete, w/c = 0.5Plain concrete, w/c = 0.6Figure 8-44Dynamic modulus versus agesThe calculated results for the dynamic modulus are plotted as a function of age inFigur...

  • Page 458

    8.5Main Commonly Used NDT-CE Techniques443xTransducer 1VRTransducer 2Impact sourceABCDFigure 8-45Surface wave velocity measurement for concrete strength assessmentwhere dBC is a function of frequency and can be visualized as the ratio of the amplitude of thesignal from the far accelerometer to th...

  • Page 459

    444Chapter 8Nondestructive Testing in Concrete Engineeringwhere V is the total volume of the mixture. Hence, one could deduce the volume componentfrom the measured velocity provide the materials of the constituents are known.From the point of view of concrete quality control, water content is one...

  • Page 460

    8.5Main Commonly Used NDT-CE Techniques445of defects in bare or overlaid reinforced concrete decks. In the testing of concrete, normallyshort-pulse radar is used, which is the electromagnetic analog of sonic and ultrasonic pulse-echomethods. In this method, the equipment generates electromagnetic...

  • Page 461

    446Chapter 8Nondestructive Testing in Concrete EngineeringInterpreting the radar image is not so easy sometimes. If the simulation technique is usedtogether with the analysis of the radar response image, the void as well as the shape of the voidcan be discovered, while it is very difficult to di...

  • Page 462

    8.5Main Commonly Used NDT-CE Techniques447Table 8-1Wavelength ranges of visiblelightWavelength (nm)Color400– 450Violet450– 480Blue480– 510Blue-green510– 550Green550– 570Yellow-green570– 590Yellow590– 630Orange630– 700Redobject to radiate or its emissivity. The amount of infrared r...

  • Page 463

    448Chapter 8Nondestructive Testing in Concrete EngineeringWhen an analysis of the surface temperature field is required, the surface temperature profile ofan object will have to be recorded and an infrared camera is required for scanning and recording.An infrared camera is a radiometer that mea...

  • Page 464

    8.5Main Commonly Used NDT-CE Techniques449There are two different ways in which infrared equipment can be deployed for thermog-raphy nondestructive evaluation, depending on the specific application envisaged. In general, athermograph can be deployed either in a passive or an active fashion. In t...

  • Page 465

    450Chapter 8Nondestructive Testing in Concrete EngineeringThe values of B and K may vary across the plane of the tile due to the variation ofthe tile/wall bound conditions, thus causing a temperature variation, which can be detected by athermal camera. Here, the lateral thermal conduction, the th...

  • Page 466

    8.5Main Commonly Used NDT-CE Techniques451(a)(b) Figure 8-47Surface temperature distribution of a debonded tile sample with the upperhalf dry and the lower half filled with water: (a) uniform heating of the inspected face,and (b) after cooling for half an hourTwo procedures for calibration are u...

  • Page 467

    452Chapter 8Nondestructive Testing in Concrete Engineering(a)(b)(c)Figure 8-48Tile with debonded area filled with airin and a lower surface temperature during heat outflow. Figure 8-48 shows thermogramsobtained on a tile sample with air defects under an external thermal stimulation. Figure8-48a...

  • Page 468

    8.5Main Commonly Used NDT-CE Techniques453Figure 8-49The lower-temperature areas (indexed by upward arrows) indicating thedefected areas filled with water or moistureFigure 8-50Thermogram indicating air-filled defect area of the external wallarrows). Due to water having infiltrated the porous ...

  • Page 469

    454Chapter 8Nondestructive Testing in Concrete EngineeringFigure 8-51Thermogram indicating several small air-filled defect areas on the externalwall of buildingMoreover, even fairly small defects can be detected by the thermography technique. InFigure 8-51, the smallest “hot spot” was only a...

  • Page 470

    8.5Main Commonly Used NDT-CE Techniques455For ceramic tiles, the emissivity is about 0.6–0.8, not high enough to ignore the effectof the surface reflection. Moreover, due to the smooth surface, more specular than diffuse,the intensity of the reflected radiation is not constant in all directio...

  • Page 471

    456Chapter 8Nondestructive Testing in Concrete Engineering(a)(b) A B C D E F GImage 1……+Time++Image2Image nFigure 8-52(a) Thermal trend analysis approach and (b) the development of the spotsover the series of images at different timesactual surface temperatures of points P1 and P2 are almost ...

  • Page 472

    8.5Main Commonly Used NDT-CE Techniques457Table 8-2The field of view and instantaneous field of view for atypical cameraDistance to ObjectField of ViewIFOV1 m0.35× 0.26 m1.1× 1.1 mm5 m1.76× 1.32 m5.5× 5.5 mm10 m3.52× 2.63 m11× 11 mm50 m17.6× 13.2 m55× 55 mmmany detectors, arranged in an...

  • Page 473

    458Chapter 8Nondestructive Testing in Concrete EngineeringI(α) = I0 cosααI0Figure 8-54The radiation from an object with the angle of viewshown in Figure 8-54, if we combine the two effects sketched above, i.e., the radiator beinglooked at by a thermal camera at an angle ofα, the expression fo...

  • Page 474

    8.6Noncontacting Resistivity Measurement Method459VoltmeterCopper rodSaturated coppersulphate solutionPorousplugReinforcementFigure 8-55Reinforcement potential measurement by the half-cell methodTable 8-3Classification of the likelihood of corrosion by half-cell potentialPotentials over an area&...

  • Page 475

    460Chapter 8Nondestructive Testing in Concrete EngineeringFigure 8-56A noncontact resistivity test apparatus for cement-based materialssetting process. In general, fresh concrete behaves essentially as an electrolyte with a resistivityof the order of 1·m, a value in the range of semiconductors, ...

  • Page 476

    8.6Noncontacting Resistivity Measurement Method461Alternating current supply AmmeterVoltmetersssElectrodes withcouplantCurrent flow fineEquipotential surfaceFigure 8-57Four-probe resistivity test of concretethis standard, the difference between two half-cell readings taken at the same location wi...

  • Page 477

    462Chapter 8Nondestructive Testing in Concrete Engineering1981; Whittington et al., 1981), and others used external force to fasten the electrodes andconcrete specimen from two ends.These measures are effective only at the beginning of experiments. As the hydrationof cement proceeds, shrinkage wi...

  • Page 478

    8.6Noncontacting Resistivity Measurement Method4638.6.2 Formulation of resistivity calculationThe resistance can be found from Equation 8-125. Since the resistance of a specimen depends onthe geometric parameters, resistance is therefore not significant for material research. The resis-tivity is...

  • Page 479

    464Chapter 8Nondestructive Testing in Concrete EngineeringSupposing the whole resistance is R, which equals all resistance elements connected in parallel.Then1/R= 1/ R1+ 1/ R2+ 1/ R3+ ···=∞i=11/ Ri= h 2πρrexrin(1/r) dr= h 2πρ ln(rex/rin)(8-128)hence, R=2πρh ln(rex/rin)(8-129)The resist...

  • Page 480

    8.6Noncontacting Resistivity Measurement Method465Transformer coreand specimenOscilloscopeData acquisitioninterfaceComputerAmplifierGeneratorV IFigure 8-60Measurement system for the resistivity test8.6.3.1 Resistivity measurements of cement specimensWhen using this system to monitor the resistivi...

  • Page 481

    466Chapter 8Nondestructive Testing in Concrete EngineeringElectrical resistivity (Ω-cm)Time (min)02004008001,0001,0002,0003,0000600123Figure 8-61Resistivity of cement pastes (w/c= 1. 0.30, 2. 040, 3. 0.50)Electrical resistivity (Ω-cm)Time (min)02004008001,2001,0002,0003,00006001,000123Figure ...

  • Page 482

    8.6Noncontacting Resistivity Measurement Method467Electrical resistivity (Ω-cm)Time (min)02004008001,0001,0002,0003,0000600Figure 8-63Repeatability of the measuring system8.6.4 Applications8.6.4.1 Hydration dynamicsNoncontact electrical resistivity measurement can be used to study the dynamics ...

  • Page 483

    468Chapter 8Nondestructive Testing in Concrete EngineeringTime (h)Capillary Porosity00.10.70.60.50.40.30.224487296120144168P0.5P0.4P0.3Figure 8-64Comparison of theoretically predicted and measured porosity (solid linesare the theoretical porosity developments from GEM-based equation; dots are the...

  • Page 484

    Problems469What are the differences among A-scan, B-scan, and C-scan?In what way is the acoustic emission method unique?How does infrared thermography detect defects below the surface of a materials?Can you give some examples of NDT in concrete engineering?How are the durability problem and NDT r...

  • Page 485

    470Chapter 8Nondestructive Testing in Concrete Engineeringrelative density,ρ= 2.3. If the reflection factor measured from the first interface at 1 day is−0.77,calculate the modulus of the concrete at that time. What will be the reflection factor at the age of 1day at the second interface?St...

  • Page 486

    Problems4716. The resistivity of a fresh concrete can be measured using the transformer principle. The cement-basedring specimen acts as a secondary in the transformer. For a concrete ring with the shape and dimensionshown in the following figure, show that the resistivity can be calculated by u...

  • Page 487

    472Chapter 8Nondestructive Testing in Concrete EngineeringA0.48 ABack interfaceFigure P8-89. A material has the following properties: for plane strain case, CL (P-wave velocity)= 5612 m/s, CT(shear wave velocity)= 3000 m/s, and densityρ= 7800 kg/m3. Find Poison’s ratio, the shear modulus,and Y...

  • Page 488

    References473Favro, L. D., Ahmed, T., Crowther, D., Jin, H. J., Kuo, P. K., and Thomas, R. I. (1991) “Infrared thermal-wave studies of coatings and composites,” Proceedings SPIE, 1467, Thermosense VIII, Orlando, FL,pp. 290– 294.Gros, X. E. (1997) NDT data fusion, London: Arnold.He, Z., Li, ...

  • Page 489

    474Chapter 8Nondestructive Testing in Concrete EngineeringLi, Z., Wei, X., and Li, W. (2003) “Preliminary interpretation of Portland cement hydration process usingresistivity measurements,” ACI Materials Journal, 100(3), 253– 257.Li, Zongjin and Shah, Surendra P. (1994) “Microcracking loc...

  • Page 490

    References475Sack, D. and Olson L. (1995) “High speed testing technologies for NDT of structures.” In Schickert, G. andWiggerhanser, H., eds., International Symposium Non-Destructive Testing in Civil Engineering(NDT-C,E), Sept. 26– 28, Berlin, pp. 43– 50Sansalone, M. (1997) “Impact-echo...

  • Page 491

    CHAPTER9THE FUTURE AND DEVELOPMENTTRENDS OF CONCRETEDue to the unique advantages of concrete, it will continue to be the most popular and mostwidely used material in the new century. The demand for concrete will keep increasing in thefuture. Subsequently, the research and development of concrete ...

  • Page 492

    9.1Sustainability of Concrete4779.1.1 Scientific utilization of more industry wasteOne way to make concrete sustainable is to utilize industry waste or by-products to replace theraw materials for making concrete, such as cement and aggregates. The industry by-productsutilized to replace cement a...

  • Page 493

    478Chapter 9The Future and Development Trends of ConcreteFigure 9-1Recycled waste glass as an aggregate for concretefume, but is much cheaper. Hence, it has great potential for future application in concrete. Moredetails on metakaolin can be found in Chapter 2.Industrial waste that can be utilize...

  • Page 494

    9.1Sustainability of Concrete479some technique to overcome the problem and ensure the quality of the concrete made of recycledaggregates.9.1.2 Low energy and low CO2 emission bindersTo reduce the environmental impact of Portland cement, efforts have been made to search forother type of binders wi...

  • Page 495

    480Chapter 9The Future and Development Trends of ConcreteTable 9-2Workability of HBC high-strength, high-performance concrete in comparison with OPCconcreteConcreteCementFly AshWaterSuperplasticizer Initial Slump Slump at 90 minTypeAmount (kg/m3) W/B (kg/m3)(kg/m3)(%)(cm)(cm)C60 HBC4140.321041651...

  • Page 496

    9.1Sustainability of Concrete481Figure 9-2Application of new HBC concrete in the Three Gorges DamPortland cement concrete mixtures, which are usually designed to obtain high strength at earlyage, are very crack-prone. The interconnections between surface and interior cracks, microcracks,and voids...

  • Page 497

    482Chapter 9The Future and Development Trends of ConcreteC1C2Mixtures of the concrete seriesControl sample50403020100After F&T testCompressive strength (MPa)C3C4C5Figure 9-3Comparison of compressive strengths of control samples and samplesthat underwent the freezing and thawing test for the c...

  • Page 498

    9.2Deep Understanding of the Nature of Hydration483504030C2 control sampleC2 after F&T testC1 control sampleC1 after F&T test20100Compressive strength (MPa)Figure 9-5Representative stress–strain curves of the concrete seriesThe degradation of concrete materials under frost attack begins...

  • Page 499

    484Chapter 9The Future and Development Trends of Concreteof hydrated cement paste. Numerical methods are commonly used to simulate the C–S–H struc-tures. As mentioned earlier, the structure of C–S–H, the major hydration product of cement,has not been revealed yet. Moreover, as concrete is...

  • Page 500

    9.3Load-Carrying Capability–Durability Unified Service Life Design Theory485Each of these methods has advantages and disadvantages. The quantum methods are nor-mally more accurate than the potential-based methods in describing atomic positions, interactionenergies, and spectroscopic properties...

  • Page 501

    486Chapter 9The Future and Development Trends of Concreteof only by the details described in the code, such as the cover thickness of a structure undera certain environmental condition. There is no scientific formulation to quantify the effect ofenvironmental conditions. In addition, the codes d...

  • Page 502

    9.4High Toughness and Ductile Concrete487Regularity of structure response to timePerformanceServicerequirementTimeFigure 9-7Regularity of concrete structure performance as function of timeof material and structure under the coupling effect of loading and environmental conditions,the study of stru...

  • Page 503

    488Chapter 9The Future and Development Trends of Concretein overlay practice. However, LMC does not offer much improvement in tensile strength andtoughness for concrete. It is still a quasi-brittle material.Even with these methodologies, the quasi-brittle nature of concrete is still there. Hence,...

  • Page 504

    References489C–S–H and self-polymerization to eliminate concrete’s quasi-brittle nature and open an era fora new generation of concrete, i.e., the fourth generation of concrete.REFERENCESAllen A. J., et al. (2004), “In-situ quasi-elastic scattering characterization of particle size effect...

  • Page 505

    490Chapter 9The Future and Development Trends of ConcreteScrivener, K. L., et al., 2004. “Quantitative study of Portland cement hydration by X-ray diffraction/ Rietveldanalysis and independent methods.” Cement Concrete Res., 34 (9) 1541– 1547.Scrivener, K. L. and Kirkpatrick, R. J. (2007) ...

  • Page 506

    INDEXAAAR, see Alkali–aggregate reactionAbnormal setting (fresh concrete), 104–105Absolute specific gravity (ASG), of aggregates,27–28Absolute volume method (mix design), 108Accelerators, 69, 76ACI equation, for predicting creep, 214–215Acoustic emission (AE) technique, 387, 419–437cha...

  • Page 507

    492IndexAggregates, (continued)in self-compacting concrete, 306shape of, 18, 31size of, 17texture of, 18, 31and unit weight, 15Aggregate/cement ratio, 18, 101Aggregate/coarse aggregate ratio, 101Aggregate fraction, 215Aggregate pullout test (bond strength), 184Aggregate stiffness, and shrinkage/c...

  • Page 508

    Index493magnesium oxychloride cement, 67–68magnesium phosphoric cement, 63–67advantages and applications of, 63–65development of, 65–67Portland cement, 34–58basic tests of, 54–58chemical composition of, 36–38dynamics of hydration, 42–51hydration, 38–42manufacture of, 34–36role...

  • Page 509

    494IndexConcrete:advantages of, 10–13classifications of, 14–15definition of, 1factors influencing properties of, 16–19admixtures, 18aggregate, 17–18cement content, 17curing, 19mixing procedures, 18water/cement, water/binder, or water/powderratios, 16–17historical development of, 1–...

  • Page 510

    Index495Dense aggregates, 29, 30Density (D):of aggregates, 27–28and compressive strength, 94of C-S-H, 485Destructive testing, 381Diffusion cell test method, 221–223Diffusivity, durability and, 217–219Diffusivity coefficient measurement,221–223Digital image processing (DIP), 445–446Digi...

  • Page 511

    496IndexFFalse setting, 104Fatigue strength, 184–189Fiber-reinforced cementitious composites (FRC),251–270defined, 251fiber-cement bond properties, 258–260FRC products, 265–270hybrid FRC, 264–265influences on properties of, 253–258mechanical properties of, 260–264Fiber-reinforced...

  • Page 512

    Index497and aggregate characteristics, 100–101ball penetration test, 99–100bleeding, 102–103and cement content, 100compaction factor, 97–98definition of, 94–95factors affecting, 100measurement of, 95–100segregation, 102setting of concrete, 103–106slump loss, 103slump test, 95–96a...

  • Page 513

    498IndexHigh-strength cementitious composites,(continued)brittleness, 279composition of, 278microstructure of, 278–279High-strength concretes (HSC), 15, 16, 270–272efficient utilization of, 483two-parameter fracture model, 354–355High-volume fly ash (HVFA) concrete, 316Hillerborg’s fic...

  • Page 514

    Index499Low-heat Portland cement (LHPC), 51Low-strength concretes, 15, 16MMacrodefect-free (MDF) materials, 276–277additives in, 16microstructures of, 162Macrostructure, 140Magnesium oxychloride cement (MOC), 67–68Magnesium phosphoric cement (MPC), 63–67advantages and applications of, 63–...

  • Page 515

    500IndexModerate-strength concretes, 15, 16Modulus of elasticity, 193–196Modulus of rupture (MOR), 174Moisture conditions (aggregates), 26Moisture content (MC):calculations, 26–27measurement of, 28–29NDT-CE testing of, 386Molecular dynamics (MD) methods, 484Monosulfoaluminate, 39MOR (modulu...

  • Page 516

    Index501principle of ultrasound, 407–408technical features and advances, 409–410wave theory for 1D case, 394–403derivation of 1D wave equation, 395–397solution for 1D wave equation, 397–403Nonhydraulic cement concrete, 1Nonlinear fracture mechanics, 346–348Normal casting method (FRCs)...

  • Page 517

    502IndexProperties of concrete: (continued)curing, 19mixing procedures, 18water/cement, water/binder, or water/powderratios, 16–17and transition zone, 155–156Pullout test (FRCs), 258–260Pultrusion (FRCs), 256Pumping concrete, 130, 131Push-out test (bond strength), 180–183P-waves, see Long...

  • Page 518

    Index503U-box test, 301V-funnel test, 298–299viscosity-modifying agent type SCC, 307Series model (modulus of elasticity), 195Setting:defined, 103of fresh concrete, 103–106abnormal setting, 104–105definition, 103–104determining time for (new method),105–106and hydration, 42of LMC, 285n...

  • Page 519

    504IndexStrength(s): (continued)uniaxial tensile strength, 171–174and mix design, 107NDT-CE testing of, 385–386shrinkage-compensating concrete, 295specific, 14tensile, 14uniaxial tensile, 171–174Strength test:control methods for, 165–166Portland cement, 57Stress, 164Stress concentration ...

  • Page 520

    Index505Toxic waste:geopolymer treatment of, 59MPC binding of, 66Transducers, calibration of, 166–167Transition zone, 152–156improvement of, 160–161and properties of concrete, 155–156significance of, 153–155structure of, 155, 156Transverse (S-) waves, 394, 398–399Triaxial stress test...

  • Page 521

    506IndexW (wet) condition, 26Weight method (fresh concrete mix design),108Well-graded aggregates, 29, 30Wet (W) condition, 26Workability:defined, 94fresh concrete, 94–106and admixtures, 101and aggregate characteristics, 100–101ball penetration test, 99–100bleeding, 102–103and cement cont...