Useofsilicagelorpolyurethaneimmobilizedbacteriaforself-healingconcrete
JianyunWanga,b,KimVanTittelbooma,NeleDeBeliea,⇑,WillyVerstraeteb
aMagnelLaboratoryforConcreteResearch,FacultyofEngineeringandArchitecture,GhentUniversity,TechnologieparkZwijnarde904,B-9052Ghent,BelgiumbLaboratoryofMicrobialEcologyandTechnology(LabMET),FacultyofBioscienceEngineering,GhentUniversity,CoupureLinks653,B-9000Ghent,Belgium
articleinfo
Articlehistory:
Received23December2010
Receivedinrevisedform14May2011
Accepted17June2011
Availableonline14July2011
Keywords:
Bacillussphaericus
Immobilization
Silicagel
Polyurethane
CaCO3Strengthregain
Coefficientofwaterpermeabilityabstract
Cracksinconcretearethemainreasonforadecreasedservicelifeofconcretestructures.Itistherefore
moreadvisableandeconomicaltorestrictthedevelopmentofearlyagesmallcracksthemomentthey
appear,thantorepairthemaftertheyhavedevelopedtolargecracks.Apromisingwayistopre-addheal-
ingagentstotheconcretetohealearlyagecrackswhentheyappear,i.e.theso-calledself-healing
approach.Inadditiontothemorecommonlystudiedpolymerichealingmaterials,bacterialCaCO3pre-
cipitationalsohasthepotentialtobeusedforself-healing.Itismorecompatiblewiththeconcretematrix
anditisenvironmentfriendly.However,bacterialactivitydecreasesalotinthehighpH(>12)environ-
mentinsideconcrete.Inthisresearch,thepossibilitytousesilicagelorpolyurethaneasthecarrierfor
protectingthebacteriawasinvestigated.Experimentalresultsshowthatsilicagelimmobilizedbacteria
exhibitedahigheractivitythanpolyurethaneimmobilizedbacteria,andhence,moreCaCO3precipitated
insilicagel(25%bymass)thaninpolyurethane(11%bymass)basedonthermogravimetricanalysis.
However,crackedmortarspecimenshealedbypolyurethaneimmobilizedbacteriahadahigherstrength
regain(60%)andlowerwaterpermeabilitycoefficient(10À10–10À11m/s),comparedwithspecimens
healedbysilicagelimmobilizedbacteriawhichshowedastrengthregainofonly5%andawaterperme-
abilitycoefficientof10À7–10À9m/s.Theresultsindicatedthatpolyurethanehasmorepotentialtobe
usedasabacterialcarrierforself-healingofconcretecracks.
Ó2011ElsevierLtd.Allrightsreserved.
1.Introduction
Concreteistheoneofthemostpopularconstructionmaterials.
However,itisquitevulnerabletocrackingbecauseofitsinherent
heterogeneityandthenon-idealserviceenvironments.Sincecracks
provideaneasypathforwaterandotheraggressivesubstanceslike
ClÀandSO2À4topenetrateinsidetheconcretematrix,theyshouldbe
repairedintimetoprolongtheservicelifeofconcretestructures.
Generally,thenormalrepairmethodsfollowtheprocedureof
monitoring,detectingandrepairing.Therepairworkwillbeper-
formedafterthecracksarediscovered.Repairagentsareapplied
fromtheoutsideandpenetrateintothecracks.Thistechnologyis
quitesuitableforrepairinglargecracks.Forsmallanddeepcracks,
itwillbedifficultforhealingagentstoreachtheinnerpart.There-
fore,analternativerepairmethodbymeansofaself-healingprocess
isbeingstrivedfor.Healingagentsareincorporatedintothe
concretematrixduringcasting.Whencracksappear,healingagents
willbereleasedfromwithintheconcreteandflowintocrackstoseal
thecracksfromtheinsidetotheoutside.Aself-healingmethodisespeciallyusefultorepairdeep-microcracksanditcanrestrain
early-agecrackstodeveloptolargecracks.
Self-healingpropertiesinconcretemaybeobtainedbydifferent
methodologies,suchassecondaryhydrationofunhydrated
cement,additionoffibers,andencapsulationofpolymers[1–5].
Anotheralternativeself-healingmaterialisbacteriallyproduced
calciumcarbonate[6–9].Comparedwiththehealingagentslike
expandedadditivesandpolymers,theproposedbio-mineral
(CaCO3)ismorecompatiblewiththeconcretematrixandmore
environmentallyfriendly.Mostbacteriaareabletoinducecarbon-
ateprecipitationundersuitableconditions[10–13].Ingeneral,
therearethreemechanismsassociatedwithbio-carbonateprecip-
itation.Oneisthedissimilatorysulfatereductioncarriedoutby
sulfatereducingbacteriaunderanoxicconditions.Thesecondis
thedegradationoforganicacids.Anotherpathwayisrelatedto
thenitrogencycle,inparticularthedegradationofureabyureolyt-
icbacteria[14].AmongthethreepathwaystoprecipitateCaCO3,
decompositionofureabyureolyticbacteriaiseasiertooperate
andcontrol[15,16].
Inourpreviousresearch,Bacillussphaericuswasfoundtobeable
toprecipitatecalciumcarbonate(CaCO3)onitscellconstituentsand
initsmicro-environmentbydecompositionofurea(CO(NH2)2)into
ammonium(NHþ4)andcarbonate(CO2À3).Thelattersubsequently
promotesthemicrobialdepositionofCaCO3inacalciumrich
0950-0618/$-seefrontmatterÓ2011ElsevierLtd.Allrightsreserved.
doi:
10.1016/j.conbuildmat.2011.06.054⇑Correspondingauthor.Tel.:+3292645522;fax:+3292645845.
E-mailaddresses:jianyun.wang@ugent.be(J.Wang),kim.vantittelboom@u
gent.be(K.VanTittelboom),nele.debelie@ugent.be(N.DeBelie),willy.verstrae
te@ugent.be(W.
Verstraete).ConstructionandBuildingMaterials26(2012)532–540
ContentslistsavailableatScienceDirect
ConstructionandBuildingMaterials
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