Research Article Causes of Early Age Cracking on Concrete...

Research ArticleCauses of Early Age Cracking on Concrete Bridge DeckExpansion Joint Repair Sections

Jared R Wright1 Farshad Rajabipour2 Jeffrey A Laman3 and Aleksandra RadliNska4

1 Department of Civil and Environmental Engineering The Pennsylvania State University 3127 Research DriveState College PA 16801 USA

2Department of Civil and Environmental Engineering The Pennsylvania State University 231M Sackett BuildingUniversity Park PA 16802 USA

3Department of Civil and Environmental Engineering The Pennsylvania State University 231J Sackett BuildingUniversity Park PA 16802 USA

4Department of Civil and Environmental Engineering The Pennsylvania State University 231D Sackett BuildingUniversity Park PA 16802 USA

Correspondence should be addressed to Jared R Wright jaredwright4gmailcom

Received 7 October 2013 Revised 6 February 2014 Accepted 11 February 2014 Published 17 March 2014

Academic Editor Andreas Kappos

Copyright copy 2014 Jared R Wright et alThis is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Cracking of newly placed binary Portland cement-slag concrete adjacent to bridge deck expansion dam replacements has beenobserved on several newly rehabilitated sections of bridge decks This paper investigates the causes of cracking by assessing theconcrete mixtures specified for bridge deck rehabilitation projects as well as reviewing the structural design of decks and theconstruction and curing methods implemented by the contractors The work consists of (1) a comprehensive literature review ofthe causes of cracking on bridge decks (2) a review of previous bridge deck rehabilitation projects that experienced early-agecracking along with construction observations of active deck rehabilitation projects and (3) an experimental evaluation of the twomost commonly used bridge deck concrete mixtures Based on the literature review the causes of concrete bridge deck crackingcan be classified into three categories concrete material properties construction practices and structural design factors The mostlikely causes of the observed early-age cracking were found to be inadequate curing and failure to properly eliminate the riskof plastic shrinkage cracking These results underscore the significance of proper moist curing methods for concrete bridge decksincluding repair sectionsThis document also provides a blueprint for future researchers to investigate early-age cracking of concretestructures

1 Introduction

Longitudinal early age cracking of concrete repair sec-tions adjacent to bridge deck expansion dam replacements(Figure 1) has been observed on several newly rehabilitatedbridge decks This research was aimed at assessing the causesof cracking in these full-depth concrete repair sections andcreating a methodology to quantify these causes Transverseearly age cracking of concrete bridge decks has been acommon problem reported by many state DOTs [1ndash11]Although many studies have been performed since the 1980sto identify the causes and effective mitigation practices forearly age cracking on concrete bridge decks very few studies

have focused on cracking in repair sections especially next torehabilitated deck expansion dams The published literatureaddressing cracking in deck repair sections is limited [12ndash17] and focuses mostly on closure pour acceleration [12]complete shear failure of reinforcing steel [14] or the dura-bility of specific repair materials such as polymer-modifiedcementitious concrete and epoxy-binder concretes [15ndash17]This paper evaluates the causes of the observed longitudinalcracking by assessing the effect of concrete material proper-ties construction and curing practices and structural designof repair sectionsThe authors maintain that the longitudinalearly age cracking observed in repair sections near bridgedeck dams is similar in nature to the transverse cracking of

Hindawi Publishing CorporationAdvances in Civil EngineeringVolume 2014 Article ID 103421 10 pageshttpdxdoiorg1011552014103421

2 Advances in Civil Engineering

Expansion joint

Crack

Crack

Figure 1 Early age longitudinal concrete cracking on concreteadjacent to bridge deck dam rehabilitations (cell phone 45 times 2inches for comparison)

newly constructed bridge decks Restrained shrinkage andthermal contraction result in tensile stress development inconcrete with the potential of cracking that is predominantlyin the direction perpendicular to the longest dimension ofthe concretemember (ie transverse for full bridge decks andlongitudinal for dam repair sections)

2 Research Objective

The main objective of this research is to identify the causesof longitudinal early age cracking in concrete deck segmentsplaced adjacent to the newly replaced bridge deck expansionjointsThis study satisfies this objective via a three-part inves-tigation into the cracking propensity of concrete repairs onbridge decks placed in the recent decade through a case studyinvolving bridge decks in Pennsylvania These three partsconsist of (1) a comprehensive literature review (2) a reviewof past bridge deck rehabilitation projects that experiencedearly age cracking and construction inspection of activebridge dam rehabilitation projects and (3) an experimentalevaluation of the fresh and hardened properties of concretein the laboratory to quantify the risk of cracking of thetwo most commonly used concrete mixtures for bridge deckconstruction and rehabilitationThis three-part investigationcan then be utilized by other researchers to investigate earlyage cracking occurrences on bridges under their purview

3 Literature Review

The factors that affect early age cracking on concrete bridgedecks are divided into three categories (1) concrete mate-rial properties (2) construction practices and (3) struc-tural design factors Each section that follows identifies theprimary and secondary contributors to early age concretecracking on bridge decks

31 Concrete Material Properties Concrete material proper-ties have been the subject of the majority of past researchfor the mitigation of early age cracking on bridge decksExcessive slump [2 5ndash7 18 19] excessive cement content[2 5ndash7 18ndash23] and excessive compressive strength [4 6 22]

are commonly recognized as the primary contributors to theearly age cracking of concrete Fiber reinforcement [6 11 24ndash27] significantly reduces concrete cracking

Previous research shows a clear correlation betweenslump and the tendency of concrete to crack at early ages [1024 28] Increased slump can increase the settlement of freshconcrete over reinforcing bars and result in cracking [10]Maximum allowable slump values of 50mm [29] 635mm[30] or 89ndash100mm [7] have been proposed

There is a strong positive relationship between concretecracking and increased cement content [6 10 20] Cementpaste is the phase in concrete that undergoes shrinkage whileaggregates do not shrink and have a lower coefficient ofthermal expansion In addition high cement content resultsin higher heat of hydration and increased risk of thermalcracking [6 18] The maximum recommended cement con-tent to prevent early age cracking has been reported as 362to 430 kgm3 of concrete However 297 to 320 kgm3 is alsonoted to do the trick [7] The literature also recommendsa cement paste fraction not greater than 035 including aircontent [6 10] (27 if excluding air content [7])

An increase in the compressive strength of concreteis usually achieved by increasing the cement content andreducing the water to cementitious materials ratio (wcm)which results in higher heat of hydration [31ndash33]and higherdrying and autogenous shrinkage as well as higher modulusof elasticity and lower creep [6 23 34] A highermodulus andlower creep result in higher tensile stresses from shrinkage[6 23 34] In addition lower wcm increases the need forproper moist curing due to lack of bleed water which resultsin higher risk of plastic shrinkage cracking [2] Several studieshave recommended narrowing the range of allowable wcmto reduce cracking as mixtures with too low or too highwcm have been shown to be more susceptible to cracking[10 21 30 35] Allowable wcm in the range 040 [5] to 048[29] has been suggested with a more recent study suggestinga wcm in the range 042 to 045 [7] Concrete strength muchhigher than that specified by structural design should not bepermitted as it exacerbates cracking [4]

Other factors that affect the heat of hydration and risk ofthermal cracking include cement type and fineness batchingtemperature ambient temperature and solar radiation [30]and coefficient of thermal expansion of concrete [31 36ndash40] Secondary concrete material properties that are knownto modestly influence early age cracking are aggregate type[1 6 7 18 21] cement type [2 6] air content [6 9 21 22]use of mineral admixtures [6 22 31 41ndash46] type of chemicaladmixtures [6 7 11 22 46ndash51] and concrete properties suchas Poissonrsquos ratio [6] and thermal conductivity [31 40]

32 Construction Practices Construction methods and siteambient conditions can contribute to early age crackingof concrete Inadequate moist curing [4 6 7 10 11 45]insufficient compaction [6 7 52] and ambient conditionsthat promote rapid evaporation of bleed water [5 6 41 53ndash55] contribute the most to early age cracking

Insufficient vibration of concrete together with insuffi-cient cover thickness over top reinforcement can increase

Advances in Civil Engineering 3

plastic and settlement cracking [52] This is especially signif-icant for concrete with high water content and high slumpUndervibration of concrete tends to cause an increase incracking while overvibration has little effect [6] A well-graded mix may mitigate these effects

Plastic shrinkage cracking is directly related to the evap-oration rate of bleed water from the surface of fresh concrete[36 53 55] Plastic cracks occur when the bleed waterevaporates faster than the rate of bleeding and as such thesurface of fresh concrete dries resulting in capillary tensilestresses [51] Evaporation rate is a function of the ambientrelative humidity concrete and air temperatures and windspeed and can be estimated based on the nomograph inACI 308R-01 [53] Special considerations such as installingwind breaks or fog sprayers should be implemented whenevaporation rates exceed 1 kgm2hr for normal concrete and05 kgm2hr for concrete with low wcm [6]

Proper moist curing reduces cracking caused by plasticshrinkage in fresh concrete Delayed curing tends to increasethe cracking risk Also use of chemical evaporation retarderscan help to decrease the number of cracks formed before thestart of moist curing Curing should begin immediately afterfinishing [6 10 45]When wet burlaps are used the first layerof presoaked burlap should be applied 10minutes after strike-off with the application of a second layer within 5 additionalminutes [7] Moist curing should continue for a minimum of7 days [4] but 14 days is preferred [56]

The sequence and length of concrete deck placement canhave some (secondary) contribution to early age cracking[22 35 52]This however is primarily relevant in continuousmultispan bridges where flexural cracking can appear innegative moment regions caused by the dead load of concretethat is subsequently placed in the positive moment area [52]Unless due to a mistake in structural design of the decktensile stresses caused by dead and live loads on the bridgeare far smaller than the restrained shrinkage stresses and areunlikely to result in early age cracking [6 10 20] Vibrationsdue to adjacent traffic lanes will only contribute to plasticcracking when concrete is undervibrated or has too high ofslump [52]

33 Structural Design Factors Structural design factors thatare recognized as primary contributors to early age concretedeck cracking include inadequate cover thickness [6 10] andimproper reinforcing bar sizes and spacing [4ndash6 10 20 2128 37 57] A top cover depth of 50ndash75mm on monolithicbridge decks has exhibited the least amount of cracking[10] At least a 50mm concrete cover is necessary to avoidsettlement cracking [6] Increasing the reinforcement barsize and spacing increases the cracking risk of bridge decks[5 10 25 58] The use of a maximum bar size of 5 andmaximum bar spacing of 150mm has been recommended[4 5 35]

Secondary structural design factors that influence earlyage deck cracking include bridge structure type [10] bridgedeck type [4 6 10 59] deck thickness [5 6 9 20 21 29 35]deck end conditions [4 10 20] girder type [6 10 20 45] and

mechanical loading [4 6 10 20] Review of the joint detailwill assist in this part of the investigation

4 Review of Past and Active DeckRehabilitation Projects

This section provides the information obtained from sitevisits to 11 past bridge deck expansion dam rehabilitationprojects and 2 active deck dam rehabilitation projects inPennsylvania The variables considered by the research teamduring these site visits include the following

(1) concrete mixture proportions and material proper-ties wcm cementitious materials content cementtype aggregate type and content mineral and chemi-cal admixtures plastic air content slump (design andmeasured at site) and 28-day compressive strength(structural design minimum required by job speci-fications and laboratory test results)

(2) construction and curing practices removal of olddam and adjacent concrete cleaning and preparingthe repair area cleaning and epoxy coating of existingrebar within the repair area installing new damand additional rebar placement compacting andfinishing concrete ambient air temperature relativehumidity and wind speed concrete temperature atplacement curing methods and duration

(3) structural design factors reinforcing bar size andspacing and cover thickness

The most important findings are provided below

41 Concrete Material Properties Records showed that thepast projectsrsquo concrete mixtures yielded laboratory tested 28-day compressive strength results of up to 394MPa whichis 43 higher than the strength required by the structuraldesign (276MPa) and 27 higher than the strength requiredby the job specifications (310MPa) A similar observationwas made during the review of active projects The excessivestrength of concretemakes itmore prone to early age crackingdue to a higher shrinkage higher stiffness and lower capacityfor creep and stress relaxation The slumps measured were inexcess of 200mm which is in contrast with the literature rec-ommendations of 50ndash100mm [7 10 29 52 57]This excessiveslump can contribute to settlement cracking To prevent suchoccurrences in the future the authors recommend enforcinga maximum allowable slump and a maximum allowable 28-day compressive strength which should not be considerablyhigher than theminimum slump and strength required in theproject specifications

42 Construction Practices During observation of construc-tion practices in active projects it was observed that thefinished concrete surfaces remained exposed to evaporationfor 30 to 40 minutes past final finish without application ofan evaporation retarder Also ambient condition monitoringand evaporation remediation equipment (ie fog sprayeretc) were not present at the site Such practices can signifi-cantly increase the risk of plastic shrinkage cracking Average


summer temperature highs in northern Pennsylvania are29∘C and the average summer lows are 17∘C Average after-noon relative humidity readings are 53 The average winterhigh temperatures are 1∘C and the average winter low tem-peratures are minus7∘C with average afternoon relative humidityreadings of 60 Without proper monitoring oversight ofconcrete placed in the afternoon during the summer plasticshrinkage can be expectedThe literature recommendation ofapplication of the first layer of presoaked burlap 10 minutesafter the strike-off and a second layer within 5 minutes [7]was not followed The QA team mentioned that it has notmandated the contractor to adhere to strict moist curingpractices on the dam rehabilitation projects It could bereasoned that similar curing practices were followed by thesame contractor on the past projects that experienced earlyage cracking

43 StructuralDesign Factors Upon reviewof the joint detailthe required longitudinal and transverse reinforcing steel inthe bridge deck dam area was calculated based on both ACI318-11 [56] and AASHTO LRFD 2012 [60] requirements fortemperature and shrinkage steel (Table 1) The calculationsindicated that the actual bar area per foot of deck basedon the as-built drawings of past projects was adequateAlso diaphragm beams were consistently located below theconcrete deck dam repair sections providing substantialsupport to withstand the load at that location The majorityof reinforcing bar sizes were number 5 and number 6 witha bar spacing of 6 inches The deck cover thickness wasbetween 50 and 75mmThese conditionsmatch the literaturerecommendations [5 6 10 35] Early age concrete crackingtherefore is unlikely caused by structural design of the deckand reinforcing bars

5 Experimental Evaluation ofBridge Deck Concrete Mixtures

The objectives of this task were to experimentally evaluatethe cracking risk of concrete mixtures commonly used forbridge deck rehabilitation These mixtures are denoted hereasMixture number 1 andMixture number 2Mixture number1 was used on all the bridge decks that experienced earlyage concrete cracking Mixture number 2 was subsequentlydeveloped and implemented by the state for use on bridgedecks With a reduction in the paste content and slightincrease in the wcm it is demonstrated thatMixture number2 provides a significant improvement in both field appli-cations (no cracking) and laboratory experiments (demon-strated below) which is expected from the literature recom-mendations [6 10 20] The experimental method providedherein can be used by future researchers to investigate thecracking propensity of their concrete mixtures

51 Materials Table 2 provides the concrete mixture propor-tions for Mixture number 1 and Mixture number 2 Mixturenumber 1 used a wcm of 043 while Mixture number 2 useda wcm of 044 The coarse aggregate was an ASTM C33number 57 crushed limestone with an oven dry (OD) specific

gravity of 270 and absorption capacity of 023 The fineaggregate met ASTMC33 with an OD specific gravity of 252absorption capacity of 202 and fineness modulus of 260Quarries were the same as outlined by previous bridge deckdam rehabilitation projects

An ASTMC150 type I cement with an ASTMC989 grade100 ground granulated blast furnace slag (GGBFS) as a 35cement replacement byweightwas used in bothmixturesThehydration of binary OPC-GGBFS binders when comparedto conventional 100 OPC binders tend to have a reducedearly age strength while the pozzolanic reaction allows thesystem to attain a similar or greater later age (28 and 90days) strength An air-entraining admixture midrange waterreducer and set retarding admixture were used to achieve atarget plastic air content of 60 and slump of 100mm

52 Experimental Methodology and Results The tests per-formed on the concrete mixtures were separated into threecategories (1) fresh properties (slump test ASTM C143-05a and plastic air content ASTM C231-10) (2) mechanicalproperties (indirect tensile strength ASTMC496-11 uniaxialcompressive strength ASTM C 39-05 and elastic modu-lus ASTM C469-10) and (3) shrinkage and temperatureproperties (drying shrinkage ASTMC157-08 restrained ringshrinkage ASTMC1581-09 heat of hydration ASTMC1064-08 and coefficient of thermal expansion ASTM C531-00)Since the wcm was greater than 042 autogenous shrinkagewas deemed negligible (60) A description of the experimentsalong with the results and discussion is provided below

521 Fresh Properties Slumps measured were between 89and 115mm and within the acceptable range of 100 plusmn 38mmThe air content range was between 54 and 64 Thesevalues are adequate when compared to literature [7 10 2952 57] and within the acceptable range of 60 plusmn 15

522 Mechanical Properties Mechanical property testingwas performed using a standard load frame All specimenswere moist cured for their duration until moments beforetesting Uniaxial compressive strength (119891

119888

1015840) of concrete wasmeasured at 1 3 7 28 and 90 days With the aid of a com-pressometer the 1- 7- and 28-day elasticmoduli (MOE) wereobtainedwithin the elastic region of the concrete stress-straincurve from the 50120583120576 point to 40 of the ultimate (failure)stress for each age (ie known as the chordmodulus)The119891

119888

1015840

and MOE measurements were obtained using 101 times 203mmconcrete cylinders Three duplicate specimens were cast for119891119888

1015840 testing and two duplicate specimens were cast for MOEtesting The indirect tensile strength testing was performedon 150 times 300mm cylinders allowed to moist cure for 28 daysbefore testing The indirect tensile strength value recorded isthe average of two duplicate specimens

Table 3 provides the results of the mechanical propertiestesting Mixture number 1 had a greater 7- 28- and 90-day 119891

119888

1015840 due to a lower wcm Mixture number 1 had alower 1-day MOE The two mixtures had comparable 7-and 28-day MOE The 28-day 119891

119888

1015840 of Mixture number 1 andMixture number 2 was 421MPa and 383MPa which are


Table 1 Temperature and shrinkage steel calculations for bridge decks

Jobnumber

Bridgenumber Direction Bar areafoot of deck

(inand2ft)

ACI tempera-tureshrinkage

(inand2ft)

LRFDtemperatureshrinkage

(inand2ft)1 1 Westbound Pier 1 1448 0027 00721 1 Westbound Pier 2 1448 0027 00721 1 Westbound Pier 3 1448 0027 00721 1 Eastbound Pier 1 1448 0029 00761 1 Eastbound Pier 2 1448 0029 00761 1 Eastbound Pier 3 1448 0029 00761 2 Westbound Pier 1 (span 1) 1448 0031 00721 2 Westbound Pier 1 (span 2) 1448 0029 00681 2 Westbound Pier 2 (span 3) 1448 0031 00721 2 Westbound Pier 2 (Span 2) 1448 0029 00681 2 Eastbound Pier 1 (span 1) 1448 0029 00681 2 Eastbound Pier 1 (span 2) 1448 0027 00651 2 Eastbound Pier 2 (span 3) 1448 0029 00681 2 Eastbound Pier 2 (Span 2) 1448 0027 00652 1 Westbound Pier 1 137 0031 00852 1 Westbound Pier 2 137 0031 00852 1 Eastbound Pier 1 137 0031 00852 1 Eastbound Pier 2 137 0031 00852 2 Westbound Pier 1 1448 0029 00762 2 Westbound Pier 2 1448 0029 00762 2 Eastbound Pier 1 1448 0027 00722 2 Eastbound Pier 2 1448 0027 00722 3 Westbound Pier 1 (Span 1) 1696 0029 00682 3 Westbound Pier 1 (Span 2) 1696 0027 00652 3 Westbound Pier 2 (Span 2) 1448 0027 00652 3 Westbound Pier 2 (Span 3) 1448 0029 00682 3 Eastbound Pier 1 (Span 1) 1696 0031 00722 3 Eastbound Pier 1 (Span 2) 1696 0027 00652 3 Eastbound Pier 2 (Span 2) 1696 0027 00652 3 Eastbound Pier 2 (Span 3) 1696 0029 00683 1 Eastbound Pier 1 (Span 1) 1333 0031 0073 1 Eastbound Pier 2 (Span 1) 1333 0031 0073 2 Pier 1 (Span 1) 1565 0033 00723 2 Pier 1 (Span 2) 1565 0032 00693 2 Pier 2 (Span 2) 1565 0032 00693 2 Pier 2 (Span 3) 1565 0033 00723 3 Pier 1 (Span 1) 1565 0033 00723 3 Pier 1 (Span 2) 1565 0032 00693 3 Pier 2 (Span 2) 1565 0032 00693 3 Pier 2 (Span 3) 1565 0033 00723 4 Pier 1 (Span 1) 1565 0035 00753 4 Pier 1 (Span 2) 1565 0033 00723 4 Pier 2 (Span 2) 1565 0033 00723 4 Pier 2 (Span 3) 1565 0035 0075


Table 2 Mixture proportions and experimental results for Mixturenumber 1 and Mixture number 2

Mixture number 1 Mixture number 2Proportions byweight kgm3

Proportions byweight kgm3

Cementitious material 390 362Cement 254 236GGBFS 136 127Waterlowast 168 160Coarse aggregate 1103 1103Fine aggregate 603 645wcm 043 044Cementitious pasteContent () 356 338

Peak heat of hydration(∘C) 36 36

Concrete COTE(strain∘C) 869119864 minus 06 844119864 minus 06

Thermal strain (120583120576) 116 113Unrestrained dryingShrinkage (120583120576) 418 378

28-day indirect tensilestrength 259 282

Age of cracking duringrestrained ring test (day) gt28 11 15 gt40 gt40 gt40

Average stress rate forrestrained ring test(MPaday)

019 008

lowastIncluding the water mass necessary to saturate aggregates

considerably larger than the structural design requirementsof 276MPa and the literature recommendations of 207 to310MPa for bridge deck applications [6] The reduced earlyage stiffness of Mixture number 2 assists in preventing earlyage cracking The reduced paste content and pozzolanicreaction of the binary OPC-GGBFS system facilitate reducedearly age stiffness while still obtaining later age stiffness andstrength values that allow the carrying of loads necessary forvehicular traffic Also these binary systems create a complexmicrostructure that makes the system more resistant tomoisture and chloride ingress [31] Asmentioned before highcompressive strengths are generally attributed to low wcmand higher cement contents These conditions favor higherstress development and higher cracking risk of concretedue to a higher heat of hydration higher drying shrinkagehigher modulus of elasticity and lower creep Overall the useof excessively strong concretes should be avoided and maycontribute to the cracking noticed in this study Table 2 showsMixture number 2 was developed for better performanceby reducing the paste content Also Table 3 shows Mixturenumber 2 has a greater tensile strength thanMixture number1 (259MPa and 282MPa resp)This greater tensile strengthmay also assist in the reduced cracking propensity of Mixturenumber 2

523 Shrinkage and Temperature Properties The heat ofhydration of fresh concretewasmeasured according toASTMC1064-08 using type T thermocouples placed mid-heightof well-insulated 152 times 152mm concrete cylinders Beforethe test all type T thermocouples were calibrated in thetemperature range 0ndash60∘C The thermocouple output wasrecorded automatically by a data acquisition unit once every30 minutes after casting concrete Two specimens were testedfor each mixture

The coefficient of thermal expansion (COTE) was mea-sured using equivalent mortar specimens in a saturatedcondition according to ASTM C531-00 Mortar bars ((25 times25 times 280mm) according to ASTM C490-11) were preparedby excluding the coarse aggregates from the previouslydeveloped concrete mixturesThis is specified by ASTMC531to limit the temperature gradients that could develop inlarger concrete prisms (75 times 75mm cross section) Mortarswere mixed according to ASTM C305-06 and cast in prismmolds using a vibrating table Gage studs were placed at theopposite 25 times 25mm ends to facilitate length measurementsTesting began after the specimens were moist cured for 14days The results from four duplicate prisms were used andaveraged to determine the COTE of each mixture in thesaturated condition The saturated specimens were heatedto a temperature of 80∘C while being fully submerged insaturated lime-water bath After at least 16 hours at 80∘C thespecimensrsquo length was recorded to the nearest 00025mmThe specimens were then submerged back into the limewaterbath and cooled to a temperature of 60∘C After at least 16hours at 60∘C the specimensrsquo lengths were recorded Thistemperature cycle (80∘C to 60∘C and reverse) was continueduntil the specimens reached a constant length upon coolingto 60∘CThis took approximately 1ndash3 weeks Once a constantlength was achieved at 60∘C prism shrinkage ceased and thetrue COTE was obtained

For drying shrinkage concrete specimens were cast in75 times 75 times 280mm rectangular molds with embedded studsThree duplicate specimens were tested for each mixtureThe initial length measurements were upon demolding at24 hours with a comparator After initial measurements thespecimens were submerged in a limewater bath for 27 daysAfter the curing period was complete the specimensrsquo lengthwas measured and drying commenced The specimens wereallowed to dry in an ambient condition of 228plusmn1∘C and 50plusmn5 RH Comparator length measurements were performedperiodically with the final measurements occurring 157 daysafter casting (ie total drying time was 129 days)

The restrained shrinkage of the two mixtures was mea-sured using a restrained ring test per ASTM C1581-09 Thetest setup includes a concrete annulus that is cast around asteel ring After 24 hours of curing under wet burlap thespecimens were demolded by removing the exterior card-board mold The concrete top surface was then sealed withaluminum tape which allowed the concrete to dry from itsoutside circumference inside an environmental chamber thatcontrolled the ambient conditions at 228plusmn05∘C and 50plusmn2RHThe resulting shrinkage deformations were measured byfour symmetrically placed strain gages mounted on the innersurface of the steel ring (at mid-height) These data allow


Table 3 Compressive strength and elastic modulus of Mixture number 1 and Mixture number 2

AGE Mixture number 1 (wcm = 043) Mixture number 2 (wcm = 044)Compressive strength MPa Elastic modulus MPa Compressive strength MPa Elastic modulus MPa

1 109 20111986404 110 17511986404

3 212 mdash 213 mdash7 287 31811986404 261 32211986404

28 421 36911986404 383 36911986404

90 431 mdash 409 mdash

calculation of the tensile stresses that develop inside concreteas a result of restrained shrinkage As the stresses inside theconcrete growwith time the stressesmay eventually reach thetensile strength of the material leading to concrete crackingThe age at which cracking occurs and the stress magnitudeat the time of cracking provide a good indication of thesusceptibility of the concrete mixture to early age crackingThree duplicate ring specimens were cast for each mixture

Table 2 provides the results for the temperature andshrinkage property experiments The peak heat of hydrationwas approximately 361∘C for both mixtures This temper-ature is reasonable for type I cement with 35 GGBFSreplacement by weight [31] The COTE provided in Table 2is the estimated concrete COTE that is calculated using thelaw of mixtures (31) based on the measured mortar COTEthe volume fraction of coarse aggregates and the COTEof limestone coarse aggregates (6119864 minus 06∘C) The measuredmortar COTE values for Mixtures number 1 and number2 were 1051119864 minus 06∘C and 1012119864 minus 06∘C respectivelyTherefore the concrete COTE for Mixtures number 1 andnumber 2 can be calculated as 869119864minus06∘Cand 844119864minus06∘Crespectively It should be noted that Mixture number 1 wasanticipated to show a greater COTE based on its greater pastecontent

Thermal strains were estimated based on the COTEand the peak temperature resulting from the heat of hydra-tion (361∘C) assuming that the concrete eventually coolsdown to the ambient temperature of 228∘C For Mixturesnumber 1 and number 2 the resultant thermal contractionstrains were approximately 116 120583120576 and 113 120583120576 respectivelyas noted in Table 2 The table also provides the results ofunrestrained drying shrinkage measurements The ultimatedrying shrinkage (at 129 days of drying) was recorded forMixture number 1 as 418 120583120576 and for Mixture number 2 as378120583120576 The drying shrinkage evolution for these mixtures ispresented in Figure 2 These values are in agreement withtypical literature results for concrete containing moderatelevels of GGBFS [46 61]

Table 2 also presents the results for the restrained ringshrinkage test For Mixture number 1 cracking occurred at 11days (at a maximum steel strain level of minus35 120583120576) for ring 2 andat 15 days (at amaximumsteel strain level ofminus34120583120576) for ring 3while no cracking occurred up to 28 days for ring 1 althoughthe steel strain climbed to minus42 120583120576 at this age for ring 1 Thestrain development between all three rings was consistentThe phenomenon of only one ring not exhibiting crackinghas been observed before and does not indicate inaccuracyof the test method [62] but corresponds to inherent material

0 20 40 60 80 100 120 140 160

Time (days)

Moist Drying

Mixture number 1

Mixture number 2

curing

minus400

minus300

minus200

minus100

0

100

200

Stra

in (120583

120576)

Figure 2 Drying shrinkage strain development over time forMixture number 1 and Mixture number 2

variability of concrete For Mixture number 2 the straindevelopment between the rings was consistent At 28 daysring 1 and ring 2 had a maximum steel strain level of minus56120583120576while ring 3 had amaximum steel strain level ofminus53120583120576 At thetermination of the test at 40 days no cracking was observedin the rings for Mixture number 2

According to ASTM C1581-09 an average stress rate atcracking can be determined based on the elapsed time atcracking or if no cracks are visible the last day of testingThe average magnitude of the restrained shrinkage stressrate for the two mixtures was calculated accordingly andis provided in Table 2 The strain development over time ispresented in Figure 3 for Mixture number 1 and Figure 4 forMixture number 2 Please note the strain value jumps inFigure 4 at 14 days and 28 days are artifacts of the DAQ andnot cracking of the concrete The average calculated stressrate for Mixture number 1 is 019MPaday which indicates amoderate to high potential for cracking according to ASTMC1581 where cracking is expected for specimens between theages of 7 and 14 days The average calculated stress rate forMixture number 2 is 008MPaday indicating a low potentialfor cracking where cracking is not expected within the first28 days The reduced paste content and slightly higher wcmof Mixture number 2 resulted in lower shrinkage and lowerrisk of cracking Considering that Mixture number 1 wasimplemented on all bridge decks that exhibited early agecracking the results obtained here indicate that a transitionto Mixture number 2 along with its decreased paste contentand higher wcm improves the durability against early deckcracking in field applications


0 7 14 21 28Specimen age (days)

Cracks initiatedminus80

minus60

minus40

minus20

0

20

40

60

Stee

l rin

g str

ain

(120583120576)

Figure 3 Restrained ring strain development over time for Mixturenumber 1 Each line denotes the average of four (4) strain readingsfor one ring Three (3) rings were tested

0 7 14 21 28 35Specimen age (days)

no cracking

minus80

minus60

minus40

minus20

0

20

40

60

Stee

l rin

g st

rain

(120583120576)

Figure 4 Restrained ring strain development over time forMixturenumber 2 Each line denotes the average of four (4) strain readingsfor one ring Three (3) rings were tested

6 Conclusions

Themain objective of this research was to identify the causesof longitudinal early age cracking in concrete deck segmentsplaced adjacent to the newly replaced bridge deck expansionjoints and to provide a blueprint of steps necessary to performthis type of investigationThe steps consisted of (1) a literaturereview of the causes of early age cracking on bridge decks(2) a review of past and active bridge deck rehabilitationprojects and (3) an experimental evaluation of the two mostcommonly used bridge deck concrete mixtures

The following conclusions can be stated

(i) Themost likely causes of the observed early age crack-ing are inadequate moist curing practices and failureto properly eliminate the risk of plastic shrinkagecracking during constructionMoist curingmust startas soon as possible and proper remediation tech-niques must be readily available at the constructionsite to limit the rate of water evaporation from thesurface of fresh concrete

(ii) The 28-day 119891119888

1015840 of the placed concrete exceeded therequired structural design strength of 276MPa by upto 43 Also the measured slumps were in excess of200mm These excessive strength and slump values

further exacerbate the risk of early age crackingConstruction specifications should include languageto limit themaximum allowable compressive strengthand slump of concrete and to evaluate the concrete forearly age shrinkage cracking

(iii) A comprehensive experimental evaluation of bridgedeck concrete mixtures showed that Mixture number2 performs better against early age cracking A lowercement paste content lower COTE lower dryingshrinkage and lower compressive strength are factorsthat have improved the performance of Mixturenumber 2

(iv) A review of the structural design of the deck andreinforcing bars suggested that the observed early agecrackingwas not likely caused by the structural designfactors

Overall an integrated approach to ensure proper selec-tion and design of concrete materials proper structuraldesign of the deck (including the repair section) and properconstruction and curing methods is needed to minimizeearly age cracking of concrete deck and repair sectionsConstruction specifications and quality assurance practicesmust be updated as needed to benefit from the availableknowledge in the literature to prevent early age crackingFurther research is needed to quantify the effect of cracks onthe durability and service-life expectancy of bridge decks andto identify the best remediation techniques and the optimumtime to repair the existing cracked bridge decks

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The experiments performed during this research occurredat Penn Statersquos Civil Infrastructure Testing and EvaluationLaboratory (CITEL) and Villanova Universityrsquos StructuralEngineering Teaching and Research LaboratoryThe researchteam would like to thank the Pennsylvania Department ofTransportation (PennDOT) personnel who contributed tothe success of this project specifically Mr Paul King theprojectrsquos technical advisor The authors thank Ms DanielleLombardi Mr Dennis Morian Mr Chris Cartwright DrShervin Jahangirnejad Mr Michael Salera and Mr DanFura for their assistance and insight The authors also thankMr Michael Casper of Penn State for his thorough editorialreview This paper consists of the major finding of the FinalProject Report no FHWA-PA-2012-006-100303 submitted toPennDOTThe contents of this report reflect the views of theauthors who are responsible for the facts and the accuracyof the information presented herein This document is dis-seminated under the sponsorship of the US Department ofTransportationrsquos University Transportation Centers Programin the interest of information exchange The US Governmentassumes no liability for the contents or use thereof


References

[1] K Babaei and R Purvis ldquoPrevention of cracks in concretebridge decks report on Laboratory Investigation of ConcreteShrinkagerdquo Research Project 89-01 Pennsylvania Departmentof Transportation Harrisburg Pa USA 1994

[2] M Brown G Sellers K Folliard and D Fowler RestrainedShrinkage Cracking of Concrete Bridge Decks State-of-the-ArtReview TexasDepartment of Transportation Austin Tex USA2001

[3] K Folliard Use of Innovative Materials to Control RestrainedShrinkage Cracking in Concrete Bridge Decks Texas Departmentof Transportation Austin Tex USA 2003

[4] R Frosch D T Blackman and R D Radabaugh Investigationof Bridge Deck Cracking in Various Bridge Superstucture SystemsPurdue University West Layfayette Ind USA 2003

[5] T Kochanaski J Parry D Pruess L Schuchardt and J ZiehrldquoPremature cracking of concrete bridge decks studyrdquo FinalReport Wisconsin Department of Transportation MadisonWis USA 1990

[6] P Krauss and E Rogalla ldquoTransverse cracking in newly con-structed bridge decksrdquo NCHRP Report 380 TransportationResearch Board Washington DC USA 1996

[7] H A K McLeod D Darwin and J Browning ldquoDevelopmentand construction of Low-CrackingHigh Performance Concrete(LC-HPC) bridge decks construction methods specificationsand resistance to chloride ion penetrationrdquo SM Report 94University of Kansas Center for Research Lawrence Kan USA2009

[8] C Meyers ldquoSurvey of cracking on underside of classes B-1and B-2 concrete bridge decks in district 4rdquo Investigation 82-2 Division of Material and Research Missouri Highway andTransportation Department Jefferson City Miss USA 1982

[9] J B Poppe ldquoFactors affecting the durability of concrete bridgedecksrdquo Tech Rep FHWACASD-812 Division of Trans-portation Facilities California Department of TransportationSacramento Calif USA 1981

[10] T R Schmitt and D Darwin ldquoCracking in concrete bridgedecksrdquo Tech Rep K-TRANKU-94-1 Kansas Department ofTransportation Topeka Kan USA 1995

[11] R Maggenti C Knapp and S Fereira ldquoControlling shrinkagecracking available technologies can provide nearly crack-freeconcrete bridge decksrdquo Concrete International vol 35 no 7 pp36ndash41 2013

[12] P Zhu and Z J Ma ldquoSelection of durable closure pourmaterials for accelerated bridge constructionrdquo Journal of BridgeEngineering vol 15 no 6 pp 695ndash704 2010

[13] D H Chen and M Won ldquoField performance monitoringof repair treatments on joint concrete pavementsrdquo Journal ofTesting and Evaluation vol 36 no 2 pp 119ndash127 2008

[14] M M Sprinkel R Weyers C Blevins A Ramniceanu and SAWeyers ldquoFailure and repair of deck closure pour on interstate81rdquo Transportation Research Record no 2150 pp 119ndash128 2010

[15] D Cusson and N Mailvaganam ldquoDurability of repair materi-alsrdquo Concrete International vol 18 no 3 pp 34ndash38 1996

[16] G Tsiatas and J Robinson ldquoDurability evaluation of concretecrack repair systemsrdquo Transportation Research Record no 1795pp 82ndash87 2002

[17] N K Emberson and G C Mays ldquoSignificance of propertymismatch significance of property mismatch in the patch repairof structural concrete part 1 properties of repair systemsrdquo

Magazine of Concrete Research vol 42 no 152 pp 147ndash1601990

[18] D Darwin J Browning and W D Lindquist ldquoControl ofcracking in bridge decks observations from the fieldrdquo CementConcrete and Aggregates vol 26 no 2 pp 148ndash154 2004

[19] D P Bentz P Lura and J W Roberts ldquoMixture proportioningfor internal curingrdquoConcrete International vol 27 no 2 pp 35ndash40 2005

[20] M A Saadeghvaziri and R Hadidi ldquoTransverse cracking ofconcrete bridge decks effects of design factorsrdquo Journal ofBridge Engineering vol 10 no 5 pp 511ndash519 2005

[21] C French L Eppers Q Le and J FHajjar ldquoTransverse crackingin concrete bridge decksrdquo Transportation Research Record no1688 pp 21ndash29 1999

[22] T R Schmitt and D Darwin ldquoEffect of material properties oncracking in bridge decksrdquo Journal of Bridge Engineering vol 4no 1 pp 8ndash13 1999

[23] P K Mehta and P J M Monteiro Concrete MicrostructureProperties and Materials McGraw Hill New York 3rd edition2006

[24] M Grzybowski and S P Shah ldquoShrinkage cracking of fiberreinforced concreterdquo ACI Materials Journal vol 87 no 2 pp138ndash148 1990

[25] C Qi J Weiss and J Olek ldquoCharacterization of plastic shrink-age cracking in fiber reinforced concrete using image analysisand a modifiedWeibull functionrdquoMaterials and Structures vol36 no 260 pp 386ndash395 2003

[26] N Banthia and R Gupta ldquoInfluence of polypropylene fibergeometry on plastic shrinkage cracking in concreterdquo Cementand Concrete Research vol 36 no 7 pp 1263ndash1267 2006

[27] B Kim and W J Weiss ldquoUsing acoustic emission to quantifydamage in restrained fiber-reinforced cement mortarsrdquoCementand Concrete Research vol 33 no 2 pp 207ndash214 2003

[28] F H Dakhil and P D Cady ldquoCracking of fresh concrete asrelated to reinforcementrdquo ACI Journal vol 72 no 8 pp 421ndash428 1975

[29] M A Saadeghvaziri and R Hadidi ldquoCause and control oftransverse cracking in concrete bridge decksrdquo Final ReportFHWA-NJ-2002-19 Federal Highway Administration Wash-ington DC USA 2002

[30] Portland Cement Association Durability of Concrete BridgeDecks A Cooperative StudymdashFinal Report Portland CementAssociation Skokie Ill USA 1970

[31] S Mindess J F Young and D Darwin Concrete PearsonEducation Upper Saddle River NJ USA 2nd edition 2003

[32] American Concrete Institute ACI 231-10 Early-Age Crack-ing Causes Measurement and Mitigation American ConcreteInstitute Farmington Hills Mich USA 2010

[33] K A Riding J L Poole A K Schindler M C G Juenger andK J Folliard ldquoEvaluation of temperature prediction methodsformass concretemembersrdquoACIMaterials Journal vol 103 no5 pp 357ndash365 2006

[34] American Concrete Institute ACI 224R-01 Control of Crackingin Concrete Structures American Concrete Institute Farming-ton Hills Mich USA 2001

[35] New York State Department of Transportation ldquoThe state ofthe art bridge deckrdquo Final Report The Bridge Deck Task ForceAlbany NY USA 1995

[36] Z Grasley Internal relative humidity drying stress gradientsand hygrothermal dilation of concrete [MS thesis] Universityof Illinois at Urbana-Champaign Champaign Ill USA 2003


[37] S L Meyers ldquoThermal coefficient of expansion of Portlandcementmdashlong time testrdquo Industrial and Engineering Chemistryvol 32 no 8 pp 1107ndash1112 1940

[38] M Won ldquoImprovements of testing procedures for concretecoefficient of thermal expansionrdquo Transportation ResearchRecord no 1919 pp 23ndash28 2005

[39] C G ZoldnersThermal Properties of Concrete under SustainedElevated Temperatures Temperature and Concrete ACI Publi-cation SP-25 1971

[40] A Radocea ldquoModel of plastic shrinkagerdquoMagazine of ConcreteResearch vol 46 no 167 pp 125ndash132 1994

[41] M D Cohen J Olek and W L Dolch ldquoMechanism of plasticshrinkage cracking in portland cement and portland cement-silica fume paste and mortarrdquo Cement and Concrete Researchvol 20 no 1 pp 103ndash119 1990

[42] C Ozyildirim ldquoComparison of the air contents of freshlymixedand hardened concretesrdquo Cement Concrete and Aggregates vol13 no 1 pp 11ndash17 1991

[43] P Lura K van Breugel and I Maruyama ldquoEffect of curingtemperature and type of cement on early-age shrinkage of high-performance concreterdquo Cement and Concrete Research vol 31no 12 pp 1867ndash1872 2001

[44] K M Lee H K Lee S H Lee and G Y Kim ldquoAutogenousshrinkage of concrete containing granulated blast-furnace slagrdquoCement and Concrete Research vol 36 no 7 pp 1279ndash12852006

[45] D P Bentz and O M Jensen ldquoMitigation strategies for auto-genous shrinkage crackingrdquo Cement and Concrete Compositesvol 26 no 6 pp 677ndash685 2004

[46] S H Kosmatka and M L Wilson Design and Control ofConcrete Mixtures Portland Cement Association Skokie IllUSA 15th edition 2011

[47] A Radlinska F Rajabipour B Bucher R Henkensiefken GSant and J Weiss ldquoShrinkage mitigation strategies in cementi-tious systems a closer look at differences in sealed and unsealedbehaviorrdquo Transportation Research Record no 2070 pp 59ndash672008

[48] F Rajabipour G Sant and J Weiss ldquoInteractions betweenShrinkage Reducing Admixtures (SRA) and cement pastersquos poresolutionrdquoCement and Concrete Research vol 38 no 5 pp 606ndash615 2008

[49] J Weiss P Lura F Rajabipour and G Sant ldquoPerformance ofshrinkage-reducing admixtures at different humidities and atearly agesrdquo ACI Materials Journal vol 105 no 5 pp 478ndash4862008

[50] K J Folliard and N S Berke ldquoProperties of high-performanceconcrete containing shrinkage-reducing admixturerdquo Cementand Concrete Research vol 27 no 9 pp 1357ndash1364 1997

[51] P Lura B Pease G B Mazzotta F Rajabipour and J WeissldquoInfluence of shrinkage-reducing admixtures on developmentof plastic shrinkage cracksrdquo ACI Materials Journal vol 104 no2 pp 187ndash194 2007

[52] M A Issa ldquoInvestigation of cracking in concrete bridge decksat early agesrdquo Journal of Bridge Engineering vol 4 no 2 pp 116ndash124 1999

[53] American Concrete Institute Guide to Curing Concrete ACI308R-01 American Concrete Institute Farmington Hills MichUSA 2001

[54] F H Wittmann ldquoOn the action of capillary pressure in freshconcreterdquo Cement and Concrete Research vol 6 no 1 pp 49ndash56 1976

[55] G E Ramey A R Wolff and R L Wright ldquoStructural designactions to mitigate bridge deck crackingrdquo Practice Periodical onStructural Design and Construction vol 2 no 3 pp 118ndash1241997

[56] American Concrete Institute Building Code Requirements forStructural Concrete ACI 318R-11 American Concrete InstituteFarmington Hills Mich USA 2011

[57] K Babaei and N Hawkins ldquoEvaluation of bridge deck protec-tive strategiesrdquo NCHRP Report 297 Transportation ResearchRecord Washington DC USA 1987

[58] D P Bentz O M Jensen K K Hansen J F Olesen HStang and C-J Haecker ldquoInfluence of cement particle-sizedistribution on early age autogenous strains and stresses incement-based materialsrdquo Journal of the American CeramicSociety vol 84 no 1 pp 129ndash135 2001

[59] T T Cheng and D W Johnson ldquoIncident assessment oftransverse cracking in bridge decks construction and materialconsiderationrdquo Tech Rep FHWANC85-002 vol 1 FederalHighway Administration Washington DC USA 1985

[60] AASHTO LRFD Bridge Design Specifications American Associ-ation of State Highway and Transportation Officials Washing-ton DC USA 6th edition 2012

[61] E Tazawa A Yonekura and S Tanaka Drying Shrinkage andCreep of Concrete Containing Granulated Blast Furnace SlagACI SP114-64 American Concrete Institute Farmington HillsMich USA 1989

[62] A Radlinska Reliability-based analysis of early-age cracking inconcrete [PhD thesis] Purdue University West Lafayette IndUSA 2008

International Journal of

AerospaceEngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

RoboticsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014


Active and Passive Electronic Components

Control Scienceand Engineering

Journal of



RotatingMachinery


Hindawi Publishing Corporation httpwwwhindawicom

Journal ofEngineeringVolume 2014

Submit your manuscripts athttpwwwhindawicom

VLSI Design



Shock and Vibration


Civil EngineeringAdvances in

Acoustics and VibrationAdvances in



Electrical and Computer Engineering

Journal of

Advances inOptoElectronics


Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

SensorsJournal of


Modelling amp Simulation in EngineeringHindawi Publishing Corporation httpwwwhindawicom Volume 2014


Chemical EngineeringInternational Journal of Antennas and

Propagation




Navigation and Observation



DistributedSensor Networks



Expansion joint

Crack

Crack

Figure 1 Early age longitudinal concrete cracking on concreteadjacent to bridge deck dam rehabilitations (cell phone 45 times 2inches for comparison)

newly constructed bridge decks Restrained shrinkage andthermal contraction result in tensile stress development inconcrete with the potential of cracking that is predominantlyin the direction perpendicular to the longest dimension ofthe concretemember (ie transverse for full bridge decks andlongitudinal for dam repair sections)

2 Research Objective

The main objective of this research is to identify the causesof longitudinal early age cracking in concrete deck segmentsplaced adjacent to the newly replaced bridge deck expansionjointsThis study satisfies this objective via a three-part inves-tigation into the cracking propensity of concrete repairs onbridge decks placed in the recent decade through a case studyinvolving bridge decks in Pennsylvania These three partsconsist of (1) a comprehensive literature review (2) a reviewof past bridge deck rehabilitation projects that experiencedearly age cracking and construction inspection of activebridge dam rehabilitation projects and (3) an experimentalevaluation of the fresh and hardened properties of concretein the laboratory to quantify the risk of cracking of thetwo most commonly used concrete mixtures for bridge deckconstruction and rehabilitationThis three-part investigationcan then be utilized by other researchers to investigate earlyage cracking occurrences on bridges under their purview

3 Literature Review

The factors that affect early age cracking on concrete bridgedecks are divided into three categories (1) concrete mate-rial properties (2) construction practices and (3) struc-tural design factors Each section that follows identifies theprimary and secondary contributors to early age concretecracking on bridge decks

31 Concrete Material Properties Concrete material proper-ties have been the subject of the majority of past researchfor the mitigation of early age cracking on bridge decksExcessive slump [2 5ndash7 18 19] excessive cement content[2 5ndash7 18ndash23] and excessive compressive strength [4 6 22]

are commonly recognized as the primary contributors to theearly age cracking of concrete Fiber reinforcement [6 11 24ndash27] significantly reduces concrete cracking

Previous research shows a clear correlation betweenslump and the tendency of concrete to crack at early ages [1024 28] Increased slump can increase the settlement of freshconcrete over reinforcing bars and result in cracking [10]Maximum allowable slump values of 50mm [29] 635mm[30] or 89ndash100mm [7] have been proposed

There is a strong positive relationship between concretecracking and increased cement content [6 10 20] Cementpaste is the phase in concrete that undergoes shrinkage whileaggregates do not shrink and have a lower coefficient ofthermal expansion In addition high cement content resultsin higher heat of hydration and increased risk of thermalcracking [6 18] The maximum recommended cement con-tent to prevent early age cracking has been reported as 362to 430 kgm3 of concrete However 297 to 320 kgm3 is alsonoted to do the trick [7] The literature also recommendsa cement paste fraction not greater than 035 including aircontent [6 10] (27 if excluding air content [7])

An increase in the compressive strength of concreteis usually achieved by increasing the cement content andreducing the water to cementitious materials ratio (wcm)which results in higher heat of hydration [31ndash33]and higherdrying and autogenous shrinkage as well as higher modulusof elasticity and lower creep [6 23 34] A highermodulus andlower creep result in higher tensile stresses from shrinkage[6 23 34] In addition lower wcm increases the need forproper moist curing due to lack of bleed water which resultsin higher risk of plastic shrinkage cracking [2] Several studieshave recommended narrowing the range of allowable wcmto reduce cracking as mixtures with too low or too highwcm have been shown to be more susceptible to cracking[10 21 30 35] Allowable wcm in the range 040 [5] to 048[29] has been suggested with a more recent study suggestinga wcm in the range 042 to 045 [7] Concrete strength muchhigher than that specified by structural design should not bepermitted as it exacerbates cracking [4]

Other factors that affect the heat of hydration and risk ofthermal cracking include cement type and fineness batchingtemperature ambient temperature and solar radiation [30]and coefficient of thermal expansion of concrete [31 36ndash40] Secondary concrete material properties that are knownto modestly influence early age cracking are aggregate type[1 6 7 18 21] cement type [2 6] air content [6 9 21 22]use of mineral admixtures [6 22 31 41ndash46] type of chemicaladmixtures [6 7 11 22 46ndash51] and concrete properties suchas Poissonrsquos ratio [6] and thermal conductivity [31 40]

32 Construction Practices Construction methods and siteambient conditions can contribute to early age crackingof concrete Inadequate moist curing [4 6 7 10 11 45]insufficient compaction [6 7 52] and ambient conditionsthat promote rapid evaporation of bleed water [5 6 41 53ndash55] contribute the most to early age cracking

Insufficient vibration of concrete together with insuffi-cient cover thickness over top reinforcement can increase




























119888


119888

1015840




119888


119888




Jobnumber


(inand2ft)


(inand2ft)














019 008










1 109 20111986404 110 17511986404

3 212 mdash 213 mdash7 287 31811986404 261 32211986404

28 421 36911986404 383 36911986404






0 20 40 60 80 100 120 140 160

Time (days)

Moist Drying

Mixture number 1

Mixture number 2

curing

minus400

minus300

minus200

minus100

0

100

200

Stra

in (120583

120576)







minus60

minus40

minus20

0

20

40

60

Stee

l rin

g str

ain

(120583120576)



no cracking

minus80

minus60

minus40

minus20

0

20

40

60

Stee

l rin

g st

rain

(120583120576)


6 Conclusions




(ii) The 28-day 119891119888








Acknowledgments



References



































































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation




































119888


119888

1015840




119888


119888




Jobnumber


(inand2ft)


(inand2ft)














019 008










1 109 20111986404 110 17511986404

3 212 mdash 213 mdash7 287 31811986404 261 32211986404

28 421 36911986404 383 36911986404






0 20 40 60 80 100 120 140 160

Time (days)

Moist Drying

Mixture number 1

Mixture number 2

curing

minus400

minus300

minus200

minus100

0

100

200

Stra

in (120583

120576)







minus60

minus40

minus20

0

20

40

60

Stee

l rin

g str

ain

(120583120576)



no cracking

minus80

minus60

minus40

minus20

0

20

40

60

Stee

l rin

g st

rain

(120583120576)


6 Conclusions




(ii) The 28-day 119891119888








Acknowledgments



References



































































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation











Jobnumber


(inand2ft)


(inand2ft)














019 008










1 109 20111986404 110 17511986404

3 212 mdash 213 mdash7 287 31811986404 261 32211986404

28 421 36911986404 383 36911986404






0 20 40 60 80 100 120 140 160

Time (days)

Moist Drying

Mixture number 1

Mixture number 2

curing

minus400

minus300

minus200

minus100

0

100

200

Stra

in (120583

120576)







minus60

minus40

minus20

0

20

40

60

Stee

l rin

g str

ain

(120583120576)



no cracking

minus80

minus60

minus40

minus20

0

20

40

60

Stee

l rin

g st

rain

(120583120576)


6 Conclusions




(ii) The 28-day 119891119888








Acknowledgments



References



































































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation




















019 008










1 109 20111986404 110 17511986404

3 212 mdash 213 mdash7 287 31811986404 261 32211986404

28 421 36911986404 383 36911986404






0 20 40 60 80 100 120 140 160

Time (days)

Moist Drying

Mixture number 1

Mixture number 2

curing

minus400

minus300

minus200

minus100

0

100

200

Stra

in (120583

120576)







minus60

minus40

minus20

0

20

40

60

Stee

l rin

g str

ain

(120583120576)



no cracking

minus80

minus60

minus40

minus20

0

20

40

60

Stee

l rin

g st

rain

(120583120576)


6 Conclusions




(ii) The 28-day 119891119888








Acknowledgments



References



































































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation












1 109 20111986404 110 17511986404

3 212 mdash 213 mdash7 287 31811986404 261 32211986404

28 421 36911986404 383 36911986404






0 20 40 60 80 100 120 140 160

Time (days)

Moist Drying

Mixture number 1

Mixture number 2

curing

minus400

minus300

minus200

minus100

0

100

200

Stra

in (120583

120576)







minus60

minus40

minus20

0

20

40

60

Stee

l rin

g str

ain

(120583120576)



no cracking

minus80

minus60

minus40

minus20

0

20

40

60

Stee

l rin

g st

rain

(120583120576)


6 Conclusions




(ii) The 28-day 119891119888








Acknowledgments



References



































































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation












minus60

minus40

minus20

0

20

40

60

Stee

l rin

g str

ain

(120583120576)



no cracking

minus80

minus60

minus40

minus20

0

20

40

60

Stee

l rin

g st

rain

(120583120576)


6 Conclusions




(ii) The 28-day 119891119888








Acknowledgments



References



































































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation










References



































































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation






































RoboticsJournal of





Journal of



RotatingMachinery





VLSI Design



Shock and Vibration







Journal of



Volume 2014


SensorsJournal of





Propagation









Research Article Causes of Early Age Cracking on Concrete...

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