Estimate the causes of crack in concrete structure based on Japan Concrete Institute (JCI) guideline

1. Safety Methodology Assessment in Civil Engineering – Assignment
By : PUTIKA ASHFARKHOIRI (putikaa@civil.eng.osaka-u.ac.jp) /ID: 28J16118
Estimate the causes of crack in concrete structure based on Japan
Concrete Institute (JCI) guideline
Introduction
There are manyconcrete structure worldwide.Toevaluate crackonconcrete structure is important
and needtobe consideredinordertodetermine crackrepairingmethod.Simpleandsystematically
investigationtodetermine cause estimationof the crackhas beendone byJapan Concrete Institute.
Theymade a procedure of investigationof cracksto the applicationof repairand strengthening.
Practical Guideline forinvestigation,Repairand Strengtheningof CrackedConcrete Structureshas
beendevelopingsince 1980 until theirlastupdatedversionin2013. The contentscoversthe
practicable investigationof crackedconcrete membersorstructures, cause estimation,evaluation,
judgementandnecessityof repairorstrengthening,selectionof the mosteffective repairand
strengtheningmethod. The mainobjective of the investigationistocollectdatafor estimationthe
cause of crackingand judge the necessaryrepairmethodand strengthening. The procedure from
the investigationof cracksisshownbelow in Fig.1

2. Crack investigation
1. Standard Investigation
The investigationiscarriedoutinshort periodbyinvestigatingthe visual inspectionandthe
existingdocumentsof the structure. The objective of the investigationistocollectdatafor
the estimationof the causesof crackingof a structure or its members.Thisisalsonecessary
for subsequentevaluationof cracks, judgementof necessityof repairandstrengthening.The
investigationcanbe done withoutanyexperimentsorlongtermobservation. We can do
standardinvestigationbyinvestigatingthe documentsof the buildingorvisual observation
of the structure.
1.1 Documents investigation
What documentsthatwe needto investigate?Below are the itemswe needtoinvestigate
The engineeringdrawingof the building
1. Designreportandspecificationof the building
Thisinclude engineeringdrawingsof the structures,structural designcalculation
arrangementsandrulesthatis usedtobuildthe structure.The designreportsalsohave
the constructionspecificationof the buildinglike materialsused,dimension,steel bar
layoutdrawing,etc.
2. Constructionrecord
The constructionrecordmeansthe conditionof the buildingwhenitsconstructed.
Recentstandardsof ISO 9000 seriespromote contractorandownerto storage the
constructionrecordsfor5 to 10 years. Therefore, the constructionrecordsare including
the materialsused,mixtureproportionsof concrete,placingof concrete,experimental
data of qualitycontrol (e.g. tensile test, etc.) andthe environmental conditionswhere
the buildingsplaced(e.g. groundprofile condition, etc.)
3. Historyof pastinvestigation(repairand strengthening)
Recordedpastinvestigationisveryimportantandvaluabletodetermine the cause of
crack. We can knowthe historyof the dailyandroutine inspectiondone byinspector.
Dailyinspectioncoversthe date atcrack occurrence,the crack propagationandthe
claimfor the residents,whileroutine inspectioncoversdefectand deterioration of
concrete whichare difficulttorecognize bydailyinspection.
4. Climate and geographical conditions
We can obtainthe climate conditionsfromthe metrological agenciesorobservations.
Temperature,relative humidity,winddirectionsandwindvelocity,etc.Forthe building
close to seashore,we alsoneedthe wave heightandwave directionsalsothe
occurrence of past storm surge or floodeventsinthose area.
5. Ground conditionsandprofile
The investigationof the groundprofile isdependingonthe geographical locationof the
building.Necessaryassessmentof the buildingplace and observationof the building
environmentisnecessary.The treatmentof the structure depends onthe surrounding
location (e.g. nearthe seashore,colddistrict, etc.).Forexample, inthe locationthat
nearto the seashore we have toconsiderthe impactof the wave heightandre-bar
corrosionbythe chloride.
1.2 Visual observation
On visual observationwe canidentifythe locationof the crack,crack width, crackpattern
and the existence of penetratingcrackby usingeye observation,photoandsimple

3. apparatusto measure the crack width. We can use crack scale to measure the crack widthor
microscope.
Fig. 2 The example of crack scale
1. Crack width
Crack widthisdefinedasthe widthmeasuredatthe surface of the structure perpendicular
to the directionof the crack. From the crack widthwe can estimate the effectof the crack
widthtothe structure.
2. Locationof crack
The locationof crack couldbe the indicatorof the cause of crack. Dryingshrinkage of
concrete,expansion of concrete bytemperature rise andleakageof watercancause the
crack. Crack that penetrate throughthe structural memberare closelyrelatedtothe degree
of serviceabilityinconveniencedue tocracks.It is necessarytoconfirmwhethercrack
penetrate throughoutthe memberof the structure.
1. Crack Pattern
The patternof the crack mightbe differentdue tothe causingof the crack. It can cause by
the chemical reactionorpropagationof salt whichmade a corrosive way.
2. DetailedInvestigation
Whenthe cause of cracking isnot possible todetermine withinthe scope of standardinvestigation.
Detailedinvestigationusuallyneedslongertime toidentifythe cause of crack thanthe standard
investigationandmore expensive. We cando detailedinvestigationby:
1. Laboratory Investigation
Bringsome sample of concrete to the laboratoryandidentifythe cause of crack by some
experiments.
2. On-site investigation
The example of on-site investigation:
For on-site investigationthere isnon-destructivetestanddestructive test.The testisused
to estimate the locationanddepthof the crack. The crack depthcan be estimatedby
ultrasonicmethodbyknowingthe time receivingof the reflectedultrasonic wavesthrough
the concrete width.
1. Measurementwithclipgage (non-destructivetest)
Strainis definedasthe ratiobetweenthe lengthof anelementbeforeandaftera force
has beenappliedtoit.Inconcrete straincan be seeninthe change of concrete or
reinforcingsteeldue totemperature,curingandforcesappliedduring itsuse.
Deformationwithinthe concrete willcause the endbarsto move relative toeachother.

4. The tensioninthe wire betweenthe barswill change accordinglythusalteringthe
resonantfrequencyof the wire.
2. Laser measurement (non-destructivetest)
We can identifycrackbyinducedandscaninglaserto the concrete.The wave is
penetratringthroughthe concrete andreflectif there isanyhole orcrack inside the
concrete.
3. Reboundhammermethod (destructivetest)
We can measure the rebounddistance byusingreboundhammerapparatusand
estimate the strengthof the concrete.If the hardnessof the surface if high,the rebound
distance islarge.Fortest hammermethod,the standard usuallyuses20polessample to
measure.concrete hardness,butincase of JCItheyuse 150 polessamples
Fig. 3 Rebound hammer test illustration
4. Infraredthermographymethod (non-destructivetest)
Infraredthermographyisequipmentormethod,whichdetectsinfraredenergyemitted
fromconcrete,convertsitto temperature,anddisplaysimageof temperature
distribution.The principle of the methodisthe surface of the concrete wall are heated
by the solarradiationandthus the temperature gradientbecome constant.
In the morning,the sunlightisreceivedbythe concrete surface,sothe temperature of
the surface concrete ishigherthanthe innersite.The conditionof the temperature is
opposite atnight-time whenthe temperature of the innersideis higherthanthe surface
sides.
Fig. 4 Temperature distribution of building cracks identification by infrared
thermography

5. 5. Impact elasticwave method (non-destructivetest)
We can investigateif there isanyvoidsorcrack onthe concrete bypenetratingvibration
wave throughthe concrete width.Thenwe will gettwoconditions:
1. If there is a crackon the concrete,thenthe periodof the penetratingwave will be
shorterand the peakof the wave spectrumpeakof will move due tothe higher
frequencyvalue,andalsohave nosingle peak.
The frequencyof the propagation(ft) canbe calculatedby 𝑓𝑡 =
𝐶 𝑝
2𝑇
Whenwe can’t estimate the frequencyof the propagation(ft),we can estimate the crack
by the concrete thickness(T),while (Cp)isthe propagationvelocityof elasticwave on
concrete (inlongitudinal direction)
Fig.5 Wave response on concrete cracks by impact elastic wave method
2. If there is no crack on the concrete,the vibrationwave will reachthe bottomof the
concrete.The wave spectrumhasonlya single peakandthe peakpositionof the
frequencyvalue islower.
We alsohave to considerabout: Structure materials,loadingsonthe structure,
environmental conditionsaroundthe structure,foundationcondition,structural
performance anddeformationandvibrationof the structure
Classificationof Cracks
1. Classificationbasedon the crack generationperiod,regularityand extendof the crack
Before we classifythe crackto the major classificationof crack,we betterknow the estimation
of crack categorybasedon theirgenerationperiod,regularityandextendof the crackto simplify
the estimationof crackcauses(see table 1).
Table 1 Classificationbasedonthe generationperiod,regularityandextendof cracks
Pattern of cracks
Cause EstimationGeneration
Period
Regularity Extend
Fewhoursto
one day
Yes
Reticular B2, B3
Surface layer A8, B2, B3, B5, B14, B16, B17
Penetration B2, B3, B4, B10, B16, B17
No Reticular B8

6. Surface layer A1, B5, B7, B8, B13, B17
Penetration B4, B10, B17
Fewdays
Yes
Reticular
Surface layer A2, A10, B15, D5
Penetration A2, A10, B16
No
Reticular A4, B9
Surface layer B7, B9
Penetration
More than
several tendays
Yes
Reticular A6, A9, B2, B3, D2
Surface layer
A6, A7, A9, A10, B2, B3, B11, B12, C1,
C2, C7, C8, D1, D3, D5
Penetration
A9, A10, B2, B3, B4, B10, B18, C1, D2,
D4, D5, D6
No
Reticular A3, A4, A6, B1, B9, C3, C4, C5, C6
Surface layer A3, A4, A5, A6, B9, C3, C4, C5, C6, D7
Penetration B4, B10, B18, D6
1.1 Classificationbasedonthe extend
The extendof crack is definedas reticularfor meshtype cracking,as surfacelayer if the depthof
the cracks islimitedtothe surface region andaspenetration if the cracks continue throughthe
section.
1.2 Classificationbasedonthe regularity
The severityof a crack can be characterizedintermsof itsdirection,width,anddepth;cracks
may be longitudinal,transverse,vertical,diagonal orrandom.Differentrisksforcrackingexist
for curedversusuncuredconcrete,andforreinforcedconcrete.Wehave toinvestigate and
determine whetherthe shape of the crack isregularor not in itsdirection,widthanddepth.
1.3 Classificationbasedonthe generationperiod
The generationperiodof crackformedafterconcrete placingfroma few hoursto more than 10
days.We can investigate the cause of the crackingbyitsgeneratingperiod.
2. Classificationbasedon the deformationand limitconsiderations
It isrequiredtoinvestigatethe deformationfactorsof concrete (dryingshrinkage, expansion,
settlement,bendingandshearing).Fromthe table 2,we can see if the cracks regionshowsthe
occurrence of shrinkage,expansion,settlement,bendingandshearing.Itisrequiredto
investigatematerial,member(suchasbeam, column,wall,slab,etc) andstructure (including
roof and foundation) forcause estimation.

7. Table 2 Classificationbasedonthe deformationandlimitsof consideration
3. Classificationbasedon mixture proportions (table 3)
Mixture proportion Standard
Cause
estimation
Rich
Cementcontentperunitvolume of concrete ismore than350
kg/m3
A2, A6, A9,
A10
Poor
Cementcontentperunitvolume of concrete islessthan350 kg/m3 A8, C3, C6, C7,
C8
4. Classificationbasedon weathercondition duringplacing concrete (table 4)
Weather condition Standard
Cause
estimation
Hightemperature The dailymentemperature duringplacingishigherthan250
C and the
ambienttemperature atplacementishigherthan 250
C
A2, B2,
B8, B17
Low temperature The dailymeantemperature atplacingislowerthan40
C
A8, B7,
B9, B13,
B16, D7
Low Humidity
The humidityislowerthan60%
A4, A9,
B8, B17
Major estimationof crack causes
Thisprocedure isa methodto estimate the cause of crack and obtaindatafor the evaluationof the
crack. There are so manycausesof cracks basedintheircategoryfromA to D. Major classificationof
causesisdividedinto5sections,whichcanbe seen intable 5
Table 5 Major cause of cracking
Major
Classification
Sub
Classification Sub-sub Number Cause
A. Materials
Used
Materials
Cement
A1 False settingof cement
A2 Heat of hydrationof cement
A3 Abnormal expansionof cement
Aggregate A4 Clayinclusioninaggregate
Deformation
factors of concrete
Limit of
consideration
Cause estimation
Shrinkage
Material A1, A2, A4, A9, A10, B1, C1, C3, C4, C5
Member A2, A9, A10, B2, B3, B8, B14, B15, B17, B1, C2, C3, C4, C5
Structure A9, B2, B3, B8, B15, C1, C2, C3, C4, C5
Expansion
Material A3, A5, A6, B1, C1, C3, C4, C5, C6
Member A7, B1, B12, B18, C1, C2, C3, C4, C5, C7, C8
Structure A7, C1, C4, C5
Settlement,
bendingand
shearing
Material A5, C1
Member
A8, B4, B5, B6, B7, B9, B10, B11, B12, B13, B16, B17, C1, C2, D1,
D2, D3, D4, D5, D6, D7
Structure B6, C1, D1, D2, D3, D4, D6, D7

8. A5 Low qualityaggregate
A6 Reactive aggregate (alkali-aggregatereaction)
Concrete
A7 Chloride inconcrete
A8 Settlementandbleedingof concrete
A9 Dryingshrinkage of concrete
A10 Autogeneous shrinkageof concrete
B.
Construction
Concrete
Mixing
B1 Non-uniformdispersionof admixture
B2 Long-time mixing
Transport
and placing
B3
Change of mix proportionat pumping
B4 Innapropriate placingsequence
B5 Rapidplacing
Compaction B6 Innapropriate compaction
Curing
B7 Loadingor vibrationbefore hardening
B8 Rapiddryingduringinitial curing
B9 Early age frostdamage
Construction
joint
B10 Innapropriate jointtreatment
Steel
Arrangement
of steel
B11 Innapropriate placementof reinforcement
B12 Lack of cover
Formwork
Formwork
B13 Deformationof formwork
B14 Water leakage (fromformwork,intosubgrade)
B15 Early removal of formwork
Support B16 Settlementof support
Others
Coldjoint B17 Innapropriate jointordiscontinuity
PC grout B18 Insufficientgrouting
C.
Environment
Physical
Temperature
and humidity
C1
Change of enviromental temperature and/or
humidity
C2
Difference of temperaturesandhumidity
betweentwosurfacesof member
C3 Repeatedcyclesof freezingandthawing
C4 Fire damage
C5 Surface heating
Chemical
Chemical
reaction C6 Chemical reactionof acidand/orsalt

9. C7 Corrosionof embeddedsteel due tocarbonation
C8
Corrosionof embeddedsteel due tochloride
attack
D. Structure
and external
force
Load
Long-term
load D1
Long-termloadwithindesignload
D2 Long-termloadoverdesignload
Short-term
load
D3 Shor-termloadwithindesignload
D4 Shor-termloadoverdesignload
Structural
design
D5
Insufficientcrosssectional areaorquantityof
steel
D6 Differential settlementof structure
Support
condition D7 Freezingheave
E. Others Others
We can determine the causesof cracksbyfollowingthe procedureof crackestimation.The crack
estimationisbasedonthe crack generationperiod,mixture proportion,weatherconditionsand
concrete deformation. We can do visual inspectionbyhearingthe soundsof concrete whenwe
knockit. If the concrete is weak,the compositions of cementsandaggregate isnotina good
proportionbecause of the false settingof mixture orthere isa hollow inside the concrete.
Another way to estimate the cause of cracking on concrete
Concrete can deteriorate foravarietyof reasons,andconcrete damage isoftenthe resultof a
combinationof factors.The followingsummarydiscussespotential causesof concrete deterioration
and the factors thatinfluence them.material limitations,designandconstructionpractices,and
severe exposure conditionscancause concrete to deteriorate,whichmayresultinaesthetic,
functional,orstructural problems.
Evaluating cracks causes and status
It isimportantto identifythe primaryconcerninregardtoany cracking.The mainconcernsare
whetherthe cracksare affectingstructural integrity,causedbyinappropriate design,aesthetically
unacceptable,orreducingdurability.We canonlyidentifythe primaryconcernafterevaluating a
crack thoroughly.The type of crackingprovidesuseful informationtohelpunderstandacrack’s
effectsonstructural stability,Summaryof the differenttype of concrete cracksandtheirpossible
causescan are presentedin table6.
Table 6 Typesof crack andtheircause
Before
Hardening
Plastic
Early frostdamage
Plasticshrinkage
Plasticsettlement
Construction
movement
Formworkmovement
Subgrade movement
After
Hardening
Physical
Shrinkable aggregates
Dryingshrinkage

10. Crazing
Chemical
Corrosionof reinforcement
Alkali-aggregate reactions
Cementcarbonationshrinkage
Thermal
Freeze/thawscycle
External seasonal temperature variations
Structural
Accidental Overload
Creep
Designloads
A crack’s statusis criticallyimportant.Active cracksmayrequire more complex repairprocedures
that may include eliminatingthe actual cause of the cracking inorderto ensure a successful long-
termrepair.Failure toaddressthe underlyingcause mayresultinthe crack’s repairbeingshort-
term,makingitnecessarytogo through the same processagain.Dormantcracks are those not
threateningastructure’sstability,butthose responsible forthe structure mustaddressdurability
issuesandtake appropriate actionif aestheticsare apriority.A crack’s environmental conditions
influencethe extenttowhichitaffectsitsstructure’sintegrity.Greaterexposure toaggressive
conditionsincreasesthe possibilityof structural instability.Cracks’sizesrange frommicro-cracks
that expose the concrete toefflorescence tolargercrackscausedby external loadingconditions.
Notingcracks’sizes,shapes,andlocationscanaidindeterminingtheirinitial causes.
1. Cracks before hardening
1.1 Crackinginplasticconcrete
Cracks that formin plasticconcrete canbe categorisedaseitherplasticshrinkage crackingor
plasticsettlementcracking.Bothof these typesresultfromthe bleedingandsegregationprocess
that occurs whenfreshconcrete isplaced.Suchcracks usuallyappearfromone tosix hoursafter
concrete placement.
1.2 Plasticshrinkage cracking
As the concrete’sheavierparticlessettle due togravity,theypushthe waterandlighterparticles
towardthe surface.Thisiscalledbleeding.If youfail tomonitorthe temperature,wind,and
humidityconditionsproperlythe evaporationrate of the surface watermayexceedthe bleed
rate,dryingout the concrete’ssuperficial layerandtherefore shrinkingitdue todehydration.
The concrete beneaththe surface layerisstill well hydrated,however,andmaintainsitsvolume.
Thisappliesopposingtensile forcestothe lowerpartof the dryingconcrete onthe surface,
causinga cracked concrete profile. These plasticshrinkagecracksare usuallyshallow andonly
from1 to 2 mm inwidth,whichmeansyoucannotrepairthemwiththe injectionmethod.They
may,however,self-heal throughcontinual cementhydrationorbythe precipitationof calcium
carbonate fromthe concrete.If the cracks are widerthan2 mmand do not self-heal,itis
importantthatyou repairthemwitha suitable coatingorflood-groutingproducttostopthem
frompenetratingthe full depthof the concrete slab.If theydobecome active theirreactionto
stressesmayresultinfurthercrackingthat weakensthe structure eitherdirectlyorbyexposing
itsreinforcementsteel tocontaminants thatwillintime corrode it.

11. 1.3 PlasticSettlementCracking
The settlementprocessisamajorfactor inconcrete’sstrengthatdifferentlevelsasitforms.
Plasticsettlementcrackingcanoccur as a resultof suchrestraintstothe consolidationof the
freshconcrete as the use of steel reinforcingbarsor formwork. Asthe concrete bleeds,the
waterworksits wayto the surface.Sedimentationthenoccursasthe aggregate and cement
move downwardsunderthe force of gravity.Thisseparationformsaweakerlayerof concrete
nearthe surface.If suchrestraintsas steel reinforcingbarsare close tothe surface and
insufficientlycoveredwithconcrete the concrete bendsbackaroundthe restraintandcracks at
the apex.Deepersectionsof concrete leadto greaterseparationbetweenthe sedimentandthe
water,so itis importanttoensure thatyou coverall superficial restraintsadequatelytoreduce
the amountof cracking.
2. Cracks afterhardening
Crackingin hardenedconcrete canresultfromanyone of many causes.These causesinclude (a)
dryingshrinkage,whichisthe maincause,(b) thermal stresses,(c) chemicalreactions,(d)
weathering,whichinvolvesheatingandcoolingandislinkedtothermal stresses,(e) the
corrosionof steel reinforcing,(f) poor constructionpractices,(g) constructionandstructural
overloads,(h) errorsindesignanddetailing,(i) externallyappliedloads,and(j) poorloadingand
storage practices.It isimportantto understandthe factorsthatinfluence the above causesof
cracking inorderto eliminate the cause andselectthe correctrepairmethod.The following
sectionsexplorethe causesof crackinginhardenedconcrete inmore depth.
2.1 DryingShrinkage
Thisis the maincause of crackingin hardenedconcrete.Thiscrackingtakesplace nearthe
restraintsdue tovolume changesinthe concrete.Whenconcrete isexposedtomoisture it
swellsandwhenitisexposedtoairwithrelativelylow humidityitshrinks,suchairdrawing
waterout of its cementpaste,whichiscement andwater.If the shrinkage couldoccurwithout
restraintnocracking wouldresult,butinmostcasesthe requirementsof structural support
makesthisimpossible.Thiscrackingisthe resultof acombinationof factorsthat influencethe
magnitude of the tensilestressesthatcause it.These factorsinclude the amountandrate of
shrinkage,the degree of restraint,the modulusof elasticity,andthe amountof creep.Additional
Evaluatingfactorsto be aware of include the type of aggregate,watercontent,bindertype,and
the concrete’smix proportionsandmechanical properties.The amountandtype of aggregate
and the cementpaste are the main influencesonthe amountof dryingshrinkage.Tominimise
the amountof shrinkage itisbestto use a stiff aggregate inhighvolumesrelativetothe cement
paste.The rate of shrinkage increaseswiththe volume of cementpaste.The aggregate provides
internal restraintstoshrinkage.Asthe outsideof the concrete coolsmore quicklythanthe inside
it shrinks,and the pressure causedbythe innersection’slackof shrinkage producestensile
stressesthat,whenexceedingthe concrete’stensile strength,cause the concrete tocrack to
relieve the pressure.
2.2 Thermal stresses
Volume differentialsare likelytodevelopinthe concrete whendifferenttemperaturesoccur
across a concrete section.The concrete thencracks whenthe tensilestressesimposedbya
change in volume differential exceedthatof itstensile strength.Thermal stressesusually
cause cracking inmass concrete structures,the maincause of the temperature differentials

12. beingthe influence of the heatof hydrationonvolume change.The heatof hydrationisthe
amountof heatreleasedduringthe cement’shydration,causingatemperature differential
to occur betweenthe concrete structure’scentre andexteriorasaresultof eithergreater
exteriorcoolingorgreaterheathydrationinthe centre.
2.3 Chemical reactions
Chemical reactionsinconcrete canbe due to the materialsusedtomake it or materialsthat
may have come intocontact withitafter ithas hardened.The cause of the cracking isthe
expansivereactionsbetweenthe aggregate andthe alkalisinthe cementpaste.The
chemical reactionoccursbetweenactive silicaandalkalis,producinganalkali-silicagel asa
by-product.The alkali-silicagel formsaroundthe surface of the aggregate,increasingits
volume andputtingpressure onthe surroundingconcrete.Thisincrease inpressurecan
cause the tensile stressestoincrease beyondthe concrete’stensilestrength.Whenthis
occurs the concrete cracks to relieve the pressure.
2.4 Structural loads
It isimportantto pay close attentiontothe wayyouload,transport,and unloadpre-cast
concrete,andhowyou secure itin place.Atany one of these stagesthe pre-castconcrete
modulescanbecome subjecttostressesthatoverloadtheirstructure.If these stressesoccur
inthe concrete’searlyagestheymayresultinpermanentcracks.Youneedtoemploylifting
proceduresthatdisperse the loadacrossthe structure inorderto reduce the riskof overload
stresses.Pre-tensionedbeamsmaypresentcrackingproblemsatthe time of stressrelief,
especiallyinbeamsthatare lessthanone day old.You needtopay particularattentionto
the storage of materialsandoperational equipmentduringthe constructionphase,asthese
may generate loadsthatexceedthose thatthe structure wasdesignedtowithstand.