Fundamentals of Concrete Curing Methods in Construction Industry: A case study form theory to practice
K. B. Khetani1, Dr. Nilesh B. Prajapati2, Dr. J. R. Pitroda31M.Tech. (Civil) Construction Engineering and Management, Civil Engineering Department, BVM Engineering College, Vallabh Vidyanagar 388120, Gujarat, India
2Associate Professor, Information Technology Department, BVM Engineering College, Vallabh Vidyanagar 388120, Gujarat, India
3Associate Professor, PG Coordinator Construction Engineering and Management, Civil Engineering Department, BVM Engineering College, Vallabh Vidyanagar 388120, Gujarat, India
***
Abstract In the past few decades, advancement in concrete technology had occur in exponential curve. This leads to the use of concretes with lower water cementitious material ratios which results into early age cracking in young concrete if special precautions are taken. In theory, concrete curing is considered as an important process in a concrete construction works, but many times in real on site construction projects concrete curing process is often considered as low priority task or process. One of the prominent reason for this could be that the cost benefits of the good curing practices are not seen immediately, rather the consequences of poor curing will only appear in the later life of the concrete structure. The aim of this paper is to summarize the various advancements in concrete curing methods in past few decades and to review published work which evaluate the curing process in real world concrete structures.
Key Words: Concrete, Curing methods, Digitization, Humiditymonitoring,InternetofThings,Moisturedetection, Realtimemonitoring,Sensors,Temperaturemonitoring
1.INTRODUCTION
Inmodernerademandsofconcreteareincreasing, whilebudgetsareshrinkingandrawmaterialsarechanging everyday.Itcanonlybeachievedthroughensuringthatthe beststrengthisgainedfromthecementitiousmaterials.Still ithasbeenobservedthatatseveralsitescuringofconcrete is left to the decision and comfort of the unskilled labour. Thereisagreatneedtoeducateallstakeholdersinvolvedin aproject,fromtheowners’boardofdirectorstothelowest level worker, that curing process can actually be a good returnvalueformoney.Itseemsillogicalifthecementisnot allowed to hydrate for the bit of water, resulting into compromise in qualityandlongevityofanysmall orlarge concreteinfrastructure.
Thefundamentalbehindtheneedofconcretecuring is very simple. Concrete undergoes a chemical process knownas"cementhydration"togainitsdesignstrengthin which it requires the presence of water in the favourable rangeoftemperaturesoveradefinedperiodoftime.Curing
is the process of preventing the loss of moisture from the concrete whilst maintaining a satisfactory temperature regime[5].Insimplewords,concretecuringisthetaskwhich encouragesconcretehydrationuntilthedesiredproperties isobtainedintheconcrete.Moisturecuringonlyinfluences theouter30to50mmofaconcreteelement'ssurface,and that is a critical element[11]. This explains that moisture controlisn'tprimarilyusedtoimproveastructure'sstrength development, but it has a huge influence on the surface permeability and hardness, therefore it restricts a structure's design properties, particularly in extreme conditions.Thisisassociatedwithanincreasingadoptionof concreteswithwater cementratiosbelow0.4,whichmaybe morevulnerabletoself desiccation.Althoughexternalwater isnecessaryinordertoobtainthemaximumbenefitofsuch aconcreteatthesurface,thiswouldnotservemorethan30 mmbelowthesurface.Internalcuringtechniquesmightbe examinedinthisscenario.
Another positive trend is that the use of supplementary cementitious materials (SCMs), which hydratemoreslowlyandoveranextendedperiodsoftime.A well hydrated SCM combination will therefore provide substantiallygreaterpotentiallong termdurability,butan SCM combination that has already been exposed to air hastilywilllikelybemuchworsethananidenticallytreated plain cement concrete. Another important factor is that curing requires work to regulate the temperature of the concrete.Structuresorslabswhichweretoocoldduringthe initialseveralhoursfollowingdeploymentwillonlyhydrate slowly,ifthatwereeven.Thismaycreateaneedofleaving forms in place for extended periods of time or adopting preventivedevicestominimiseplasticshrinkagecrackingin a concrete. When the concrete structure is allowed to get excessivelyhotinthefirstfewhoursofhydrationprocess,it is more liable to cracks depending on the temperature differences between the internal core temperature and surfacetemperature.Concretewhichhydratesunderhigher temperatures seems to be more vulnerable to harmful chemicalreactionsandexternalchemicalreagentattack.
Whileitisrecognisedthatcuringisanimportantco factor, it does come at a cost and may cause delays in the
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constructiontimeline.Itisalsobelievedthatalackofcuring hasnomeasurableimpactontheconcrete'squalityorthe payvariablesassociatedwithanyofit.Whenexpensesand schedules are restricted, it's easy to underestimate the significance of curing. Concrete mixtures might be less flexiblethaninthepastduetothegreaterdemandsplaced on them. As a result, any activity that improves hydration andthusperformancewhileloweringthechanceofcracking is more significant than it has ever been. Finally, it's important to check whether the concrete curing process wentsmoothlyornot.Directmethods,suchascalculating the volume of curing compound per unit area, are easy to track, but they completely disregard regional differences, windliabilities,orevenifthejobwasfinishedwithintime limits. If methods other than curing substances are being adopted,theconcernofhowlongtheymustbeusedarises. Althoughperformance basedsolutionstoansweringthese issues have some appeal, they are often costly and inefficient. Payments are also considered a matter of assessment. Many agreements do have a part of the specificationsthatmakescuringapayelement,butwithout preciseassessment,it'shardtodeterminewhenpaymentis due,andthecashvalueassociatedtoitiseventuallyimpact worse than the potential damage to the building if it's ignoredorperformedinadequately.Curingisagreatideain theory, but in actuality, we must balance the system's implementationandachievementwithboththeeffortand costrequiredtogetthere
2. SCENARIO OF CONCRETE CURING IN REAL WORLD
2.1 Hot Climate
Alsayed et al. (1994) presentedresearchontheimpact of desert style curing upon normal concrete. One set was sprayed twice per day every day, another was burlap wrappedandsprayedtwiceperday,athirdwasenclosedby plastic,andthelastwaslefttotheenvironment.Thesamples weresubsequentlyexposedtoanaridclimateforayear.The resultsalongwithsomeoftheobservationsprovidedinthis paper reveal that the extent of the influence of curing on sample strength is influenced significantly by sample size, withhighereffectsshowninsmallersamples.Thedryersets' high early strengths may not be surprising, as a sample examined dry would often have greater strengths versus equivalent,wettedsamples.Theresultsshowthattheplastic sheets provided little moisture protection. The fact that perhapsthespecimencoveredinplastichadpoorabsorption results supports this argument. It brings up the question aboutwhethertheplasticwaseffectivelyenclosedallaround specimens to minimize water evaporation, given self desiccationisunlikelyataw/c0.45,andotherresearchhas demonstrated the advantages of efficient plastic wrap. Anotherpossibilityisthatthetimespanacrosswhichitwas usedwasinsufficient.Theweatherduringthetestperiodis not described in detail in the research, but the huge
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expansionsthatbeganaroundfourmonthsaregreaterthan theactualshrinking.Thisunusualpatterncanonlyreallybe explained by the variation in temperature and relative humidity status, which are most likely due to seasonal changes.Theresultswill beusefulinthatthosewhoshow how important it is to consider all of the aspects that can effect a mixture's performance, and then how such performancehasbeenmeasured.[2]
Hoppe et al. (1994) examinestheaccuracyofdurability indextriesinSouthAfricawhenitisusedtodeterminethe efficiencyofonsitecuring.Allofthetrialresultssuggestthat openconcreteseemstobemorepermeableversusconcrete that has been kept moistened all of the time. The curing component was only slightly beneficial in summer placed concrete,and,unexpectedly,performedworseinmoderate weather placements than exposed surfaces. A delayed spraying of the compound is thought to have caused solid concrete to harden sufficiently before even being treated. Later rainfall in the mild weather helped to hydrate the treated surfaces while keeping them dry. Improper application of curing chemicals, such as prolonging implementation,tendstohaveresultedinminimalbenefit, soonastheweatherismild.Alackofpropercuringresulted in a significant reduction in the system's maximum durability.[7]
With attempt to optimize specifications, Al Gahtani (2010) aimedtoassesstheinfluenceofcuringprocedureson concretequalities.Thegoalofcuringistokeeptheconcrete moist enough to allow hydration of the cement and supplementary cementitious material (SCM). In hot, dry areas,thisseemstobechallengingtodo.Curinghasagreater impactonpermeabilitythanitdoesonstrength.Forallofthe cementitioussystemsevaluated,providingprotectionwith curingsubstancesappearedtobemoreeffectivethanusing burlapthroughaspectsofshrinkage,strengthgain,andpulse velocity.Similarly,dryingshrinkagewasgreatestinburlap specimens and minimum in acrylic curing compound samples,whilethedifferenceswereminor.Theacryliccured samples had the highest concrete strength and ultrasonic pulsevelocity,whiletheburlapsampleshadthelowest.[1]
2.2 Cold Climate
The influence of SCMs, dose, and cure on scaling performancewasexploredbyBoyd and Hooton(2007).The study'smaingoalwastolinktestmethodsandproceduresto fieldperformance,howeveritdidshowthatusingacuring chemicalimprovesscalingresistance.Scalingresistancewas found to be reduced when SCM content was increased in laboratorystudies.Therewasnoevidenceofalinkbetween finishing time and scaling resistance. Apparently varying curingofthelaboratory testedsamplesshowedaconsistent trend. These samples treated using curing solution had superiorscalingresistancethanthosecoatedwithburlapand plastic. Only the fifty percent slag mixture, which was
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subjectedthroughoutthefieldfortenyearsand600freeze thaw cycles, displayed any apparent and modestscaling, whichwaslimitedtothepartsnevercuredwithcuringagent. Flyashlookedtoboostsurfacestrength,butslagappearedto decreaseit.Finishingvariationshadaminorimpact,whereas curinghadagreaterimpact.Thesamplescuredusingcuring compoundonceagainproducedthegreatestresults.Itwas highlightedthatlayingaslabwellaheadofitsfirstfreezing incidentmightbesupposedtoperformwellthanlayingaslab subsequenttothewinterseason.[9]
Bouzoubaa et al. (2011) investigated the impact of curingregimesonsaltscalingofpavementcombinationsin the field and in the lab. The fly ash and compound combinations performed poorly, and they were more susceptibletomaturityandcuringcomparedtoconventional concrete. Despite the fact that the research suggests that usingSCMsimprovesprospectivedurability,thisisnotthe case. These observations are most likely the product of a complexofthefollowingvariables.Scalingresistanceismost likely regulated by the degree of hydration in the system, with considerable benefits achieved from tiny hydration increments, particularly in some more developed systems. Such changes seem unlikely to impact influence on performance. SCM containing solutions are known to take longertohydrate.Thisindicatesthattwodaysofburlapare unlikelytobeenoughtoproducethemoisturelevelsinthe upperlayersrequiredforscalingresistance.Intermsofthe levelofsaturationjustatexterioraswellasthepossibilityof crackingafterrapiddryingwhenevertheburlapispeeled, curing compounds are anticipated to offer equal curing substantiallyhigherthantwodaysbeneathburlap.[3]
2.3 High Performance Concrete
Huo and Wong (2006) examinedthedynamicsofhigh performance concrete (HPC) samples exposed to various curing processes at an early age. Shrinkage, temperature change, and evaporation rate were all measured. Both relative drying & shrinkage effects of such typical curing techniques were demonstrated in this study. The need of earlyprotectionforroughlysevendayswasemphasizedonce again.[8]
Poursaee and Hansson (2010) wanted to see if increasing curing time from 3 to 7 days was useful or necessary. For 100 weeks, samples were monitored for internalstrain,moisturecontent,andtemperature.Thestrain rose over time in all prisms, with the control combination havinglowerstrainsandtheslagandflyashcombinations havinglittledifference.Therewasnoevidentpatterninthe influenceofwetcuringperiodoninternalstrain,accordingto the data. The resultsof this studyare unexpected, andthe reasonsforthelackofapatternovercuringperiodcannotbe justifiedbasedontheevidencesupplied.[14]
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Zhimin and Junzhe (2011) exploredtheroleofsteam curingwithbinderspeciesonconcretestrengthpropertiesat various depths. Many of the outcomes are in line with previousresearch,whileothersaresurprising.Theternary mixture's poor performance in relation to the OPC system does not match the given data. It's likely that perhaps the chemical of the concrete mixture ingredients made them unsuitable for combining in the proportions chosen. This adverseconsequenceofsteamontheoutermostlayer,onthe other hand, is consistent with previous experience. Steam curehadadeleteriouseffectatalldepthsstudied,according to unpublished research by the author. This has been explainedasaresultoffasterhydration,whichresultedina coarser,moreporousmicro structure.[6]
2.4 Performance Parameters
Petrou et al. (2001) looked at bridge deck cracking. Impropercuringwasindeedamaincausetocrackingin4of the decks studied, according to the study. In addition, structuraldeflectionsmustbebalancedbymixturestiffness, alongwithstructuralstrength,permeability,&crackingrisk. The discussion of the impact of slump upon cracking risk mustbehandledwithcaution.Thepaste waterproportionof asolutionhasadirectinfluenceonshrinkage.Thereexisteda connection among slump and cracking when slump was predominantlyregulatedbywatercontentinacombination, however this link is no longer valid in today's technology, whenslumpisregulatedbymixproportions.[12]
InSouthDakota, Johnston and Surdahl (2007) explored therelationshipbetweenanumberofparametersthataffect cracking within continuously reinforced concrete (CRC) pavement.Thefindingsbackwiththetheorythatavarietyof conditions can increase the chance of cracking. Although someparameters,suchastemperature,haveagreatimpact, theyaredifficulttomanage;hence,modifyingthesomewhat smaller variables that can be modified, including such acceleratedcuring,couldstillhaveasignificantimpact.[10]
To track curing, Radlinski et al. (2008) employed maturity measures. Maturity is a method for predicting a concrete'scompressivestrengthdependingontheproductof temperatureanddurationundergonebya mixture.Oneof thegoalsofthestudywastoseeifthemethodologycouldbe usedtomonitormixeswithaddedcementitiousingredients. The heat profile's lack of sensitivity towards curing is remarkable.Theauthorsattributethistotheavailabilityof water in the system, yet more extra water for hydration mightresultinahigherhydrationheat.Thespecimenthatis permitted to be evaluated dry, from the other side, is predicted to have better instead of lesser strengths. It's possible that the effect exists but is less than the data collecting precision. The consequences of intermittent wetnessshouldbecarefullyconsidered.Thestudyreliedon compressionstrengthmeasurementson150mmcylinders. Examinationofporosityatthefacesofsuchvarioussamples
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wouldalmostcertainlyhaveresultedinadifferentoutcome. Theresultsindicatetheimpactofcuringtechniquemostlyon long period hydration of a cementitious material once again.[15]
Bouzouba et al. (2010) analysed the effect of mixture parametersoncarbonationprocessesinbothlaboratoryand field testing. Curing for longer than three days appears to providelittlebenefitintermsofcarbonation.It'salsoworth noting thatcarbonation inhigher gradeconcrete mixtures waslessaffectedbyflyashlevels.[4]
Peyton et al. (2012) likewise looked into bridge deck cracking.In2005,fiveunder constructionbridgedeckswere evaluated to see which of these conditions contributed to cracking:Structuraldesign,materialqualities,proportioning of mixtures, construction methods, and curing methods Despitethefactthatallofthebridgesweretreatedusingboth curing chemical & moist burlap and plastic, considerable crackingwasnoted,particularlyinthosewherecuringbegan late. This underlines the importance of properly timing curingtogetthebestbenefit.[13]
The goal of Tamayo's (2012) research was to see if lithiumsilicateadditivesraisestheriskonplasticshrinkage crackingacross4Arkansasbridgedecks.Aportionofevery floor had been sprayed using lithium silicate like a completing aid, while the rest was treated with standard curingchemical.Althoughthelithiumsilicatewasemployed toreducecrackingratherthanasacuringagent,thisclaims toalsobeproductiveandcost efficient.[16]
3. CONCLUSION
Concretecuringisvitalforconstructionswhichhavebeen subjected to harsh conditions, particularly in terms of ultimate durability. In dry regions, self desiccating combinations must be avoided because supplementary water techniques may indeed be hard to implement. The probabledurabilityofaconcretestructurecanbedrastically decreasedifcuringtreatmentsareappliedlate.Somestudies foundthatcuringcompoundsperformedmuchbetter,while manyothersclaimedburlapandplastictobepreferable.If curingsubstancesareplacedbeforebleedinghasstopped, effectiveness is likely to suffer. Curing chemicals tend can provide protection comparable to moist curing for 3 to 7 days. Curing is necessary for the most quality parameters over 3 to 7 days, with extended duration required for concretecontainingSupplementarycementitiousmaterials. Althoughsteamcuringcanincreaseitsstrength,itcanalso reduce durability. The possibility of cracks can indeed be reduced with proper curing. Lithium silicate compounds tend to be beneficial in preventing bridge deck damage. Optimizingandregulatingthepaceofthecuringappearsto improvecuringeffectiveness.
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damagedconcretewithpost fire curing”,Construction and Building Materials, 237, 117564. doi.org/10.1016/j.conbuildmat.2019.117564
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