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SWrucWural Analysis of HisWorical ConsWrucWions – Jerzy Jasieńko (ed) © 2012 DPNH ProcławH PolandH ISSN 0860-2395H ISBN 978-83-7125-216-7

abiAMINATIlN lF abeUMIaIFIba RbPAIR MlRTARSW A NbW bXPbRIMbNTAi ANa NUMbRICAi ANAiYSIS mietro BoccaNI pilvio salenteOI Alessandro drazziniPI Andrea AlbertoQI sincenzo ai sastoR=

=

ABSTRACT =An= innovative= preliminary= design= stage= laboratory= procedureI= developed= at= the= kon= aestructive=qesting=iaboratory=of=the=molitecnico=di=qorinoI=for= the=preJqualification=of=repair=mortars=applied=to=historical=masonry=buildings=is=here=describedK=qhe=tested=repair=mortars=are=suitable=for=use=with=new=dehumidified=plasters=as=they=can=stop=the=rising=damp=effectsI=caused=by=capillary=action=on=historical=masonry= wallsK= iongJterm= plaster= delamination= frequently= occurs= as= a= consequence= of= the= non=compatible= mechanical= characteristics= of= mortarK= mreventing= this= phenomenon= is= the= main= way= of=increasing= the= durability= of= repair= workK= qhe= use= of= similar= materials= to= historical= ones= in= terms= of=mechanicalI=chemical=and=thermoJhygrometric=performances=is=preferableK==qhe=procedure=consists=of=the=application=of=static= loads=to=mixed=stone=blockJmortar=specimens=with=particular= characteristicsI= in= terms= of= geometry= and= adhesion= at= the= interfaceI= with= the= continuous=monitoring= of= the= longitudinal= and= transverse= displacementsK= A= numerical= simulation= based= on= the=cohesive=crack=model=was=used=to=follow=the=experimental=dataI=in=order=to=describe=the=evolutionary=phenomenon=of=deJbonding=as=a=function=of=a=small=number=of=parametersK=qhe= methodology= is= currently= being= used= at= pacro= jonte= di= sarallo= ppecial= katural= oeserve=ErkbpCl=heritage=siteF=in=miedmont=EftalyFK=

=heywords: aurabilityI eistorical masonry structuresI aehumidified mortarI iongJterm plaster

delaminationI Cohesive crack model NK INTRlaUCTIlN =jasonry=walls=of=historical=buildings=are=often=subject=to=rising=damp=effects=due=to=capillary=action=or==rain=infiltrationK=qhe=decay=and=delamination=of=plasters=frequently=occur=as=a=result=of==dampnessK=qhe=restoration=market=offers=a=great=number=of=dehumidified=repair=mortars= to=use=with=new=transpiring=plastersI= the= mechanical= characteristicsI= of= which= howeverI= have= not= been= compared= carefully=with=those=of=historical=masonry=supportsK==qhe=goal= of= this= experimental= and=numerical=analysis= was= to= focus=attention=on= the=preliminary=preJqualification= of= repair= materials= before= their= useI= in= order= to= avoid= any= mechanical= or= physical=incompatibilityI=and=at=the=same=time=to=guarantee=the=maximum=durability=of=the=restoration=work=xNzK==qhis=experimental=study=is=being=carried==out=at=the=pacri=jonti=di=sarallo=rkbpCl=heritage=site=EcigK=NFK=pituated=at= the=top=of= the=hill= above=the=town=of=sarallo= in=miedmont= EftalyFI=pacro=jonte=is= an=

================================================N=cull=mrofessorI=molitecnico=di=qorino=–=aepartment=of=ptructuralI=Building=and=deotechnical=bngineeringI=

pietroKbocca]politoKit==O=cull=mrofessorI=molitecnico=di=qorino=–=aepartment=of=ptructuralI=Building=and=deotechnical=bngineeringI=

silvioKvalente]politoKit==P=oesearch=AssistantI=molitecnico=di=qorino=–=aepartment=of=ptructuralI=Building=and=deotechnical=bngineeringI=

alessandroKgrazzini]politoKit==Q=mha=ptudentI=molitecnico=di=qorino=–=aepartment=of=ptructuralI=Building=and=deotechnical=bngineeringI=

andreaKalberto]politoKit=R=qechnician=laboratoryI=molitecnico=di=qorino=–=aepartment=of=ptructuralI=Building=and=deotechnical=

bngineeringI=vincenzoKdivasto]politoKit=

SOV=

artisticJreligious=complex=consisting=of=QR=chapelsI=which=contain=with=frescoes=and=sculptures=that=tell=the=story=of= the= life=of=ChristK=qhe=aim=of= this=particular=architectural=site=was= to=reproduce=the=holy=sites=in=malestine=where=Christ=had=spent=his=early=lifeK=Constructed=between=the=NRth=and==NUth=centuries=by= the= most= important= artists= in= miedmont= and= iombardy= of= that= periodI= pacro= jonte= is= also=a=wonderful==example=of=park=gardensK=qhe=chapels=were=constructed=very=simplyI=sometimes=making=use=of=natural=materialsI=stone=or=brick=wallsI=with=wooden=roofs=and=stone=surfacesK=Because= of= the= rising= capillary= dampI= the= freezeJthaw= cycles= and= = the= abundant= rain= and= snow=precipitations= that= characterize= this= mountain= areaI= the= historical= plaster= of= the= chapels= has= been=subjected=to=progressive=material=decay=over=a=long=period=of=timeK==pince= OMNMI= a= research= group= at= the= molitecnico= di= qorinoI= composed= of= engineersI= architectsI=physicists=and=chemistsI= have=worked= = together= on=the=obJcobpClp=projectI= and=have=studied= = the=decay= of= this= plaster= in= different= scientific= waysI= through= sophisticated= non= destructive= in= situ= and=laboratory=testsK=qhe=aim=of=the=research=was=to=offer=appropriate=technical=solutions=to=stop=this=decay=and=to=restore=the=masonry=surfaces=using=compatible=and=durable=materials=and=techniques=in=order=to=save=the=frescos=in=the=chapelsK=A=part=of=this=projectI=the=research=group=of=the=iaboratory=of=non=aestructive=qesting=jaterials=at=the=molitecnico= di= qorino= has= carried= out= particular= fatigue= tests= on= ad= hoc= mixed= stone= blockJmortar=specimens= in= order= to= evaluate= the= mechanical= adhesion= of= the= new= repair= mortars= to= the= masonry=supports= xOzK= =rnfortunatelyI= some= recent= restoration=work= on= decayed=plasters= have=already= shown=their= poor= durability= because= of= the= incompatibility= of= the= employed= repair= mortarsI= which= are= not=suitable=for= the=thermal=or= mechanics=stresses=encountered=at= the=siteK=qhis= incompatibility=has= led=to=early=delamination=and=decay=of=these=new=repair=plastersK==

==

FigK N qhe=pacri=jonti=di=sarallo=qransfiguration=Chapel=

=OK SPbCIMbN PRbPARATIlN ANa bXPbRIMbNTAi SbTUP =qhe= geometry= of= the= stone= blockJmortar= specimens= is= shown= in= cigK=OK= qwo= mixed= specimensI=prepared= by= = joining= a= stone= block= = Esimilar= to= that= of= the= pacro= jonti= masonriesF= to= symmetrical=layers=of=repair=mortar=on=the=two=shorter=vertical=sides=of=the=stone=block==have=been=testedK=qhe=stone=surfaces=to=contact=with=the=mortar=are=been=treated=with=carvings=shown=in=cigK=O=in=order=to=improve=the=adherence= of= the= strengthening=productK= qhey= have= been= tested= of= dehumidifying= mortar= layers=were=not=applied=in=complete=adherence=with=the=stone=block=supportK=qhey==were=instead=applied==in=symmetrical=and=regular= discontinuity=at= the=bottom=and= = top=of= the=specimenK=qhese=discontinuities=behave= like= notches= that= which= are= able= to= trigger= multiple= crack= propagationK= qhe= aim= of= these=particular= mixed=specimens=and=tests= was= to=simulate= the=adherence= capacity= of= each= repair= mortar=applied=to=a=specific=masonry=wall=as=dehumidified=plasterK==

SPM=

=

====

=

FigK O deometry=of=the=specimens==

======= =

FigK P deometry=of==the=wedges==qhe=preJblended=mortarI=chosen=from=among=the=main=ones=on=the=marketI= is=a=transpirant=base=made=from= natural= hydraulic= lime= and= bcoJmozzolanI= which= is= suitable= for= the= restoration= of= = historical=masonry=damaged=by=rising=capillary=damp=and=sulphate=saltsK=voung’s=modulus=of=this=repair=mortarI=evaluated=according= to=rkfSRRSI=was= QPUM=jmaK=qhe=compressive=strengthI= evaluated=according= to=rkfSRRSI=was=PPIU=jmaK=qhe=above=mentioned=values=were=evaluated=OU=days=after=the=castingK==

SPN=

qhe= mixed= pieces= were= instrumented= with= the= two= symmetrical= couples= of= inductive= displacement=transducers=shown=in=cigKR=and=cigKSK=lne=transducer= EpmMF=per=side=was=arranged=horizontally=in=the=lower=part=of=the=specimen=and=connected=between=the=two=opposite=mortar=layersI=in=order=to=measure=the=displacements=due=to=bulgingK=qhe=other=transducers=EpmsFI=one=per=sideI=were=placed=vertically=on=the=stone=blockK==

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FigK R bxperimental=setup FigK S qransducer==position qhe= static= compressive= tests= were= performed= with= the= aid= of= a= ORM= kk= servo= controlled= machineI= =Emodel=UNM=jqpFK=jonotonous=compression=tests=were=carried=out=by=the=controlling=the=horizontal=opening= Epml= transducersF= with=a= speed= opening=at= MIMMMN= mmLsK= qhe= specimens= were= subjected= to=static=tests=after=OU=days=of=maturationK=qhe=lower==mortars=layer=support==was=made=up=of==a=double=system=of=steel=wedges=E=see=in=cigK=O=and=cigK=PFI=coupled=with=and=without=qeflonK=qhe= mixed= specimens= were= labeled= with= “pj”= Eptone= blockJjortarFI= followed= by= a= number=indicating=the=orderK=qhese=two=static=tests=represent=the=first=step=of=this=experimental=study=which=is=currently=in=progressK=qhe =next =steps =will =concern =the =same =type =of =mixed =specimensI =but =this =time = =subjected =to =cyclic =fatigue=testsK==PK NUMbRICAi SIMUiATIlN TeRlUGe Teb ClebSIVb CRACK Mlabi =qhe= most= realistic= method= used= today= for= the= numerical= simulation= of= mortar= and= stone= block=fracturing= = is= the=cohesive=crack=modelI=also=known=as= the=Barenblatt=–=augdale=J=eillerborg=model= =for=quasiJbrittle=materialsK=fn=the=present=workI=the=crack=initiation=criterion=is=assumed=asW==

= NO

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M =÷÷ø

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æ+÷

÷ø

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st ffts = ENF=

=where==σM==and==τM==are=stresses=evaluated=along=the=directions=normal=and=tangential=to=the=interface=and=ft and=fs=are=the=related=strengthsK=qhe=point=where=equation=ENF=is=satisfied=is=called=the=fictitious crack tipK==According= to= this= method= the= cohesive= stresses= acting= on= the= nonJlinear= fracture= process= zone=Eshortened=cmwF=are=decreasing=functions=of=the=effective=value=of=the=displacement=discontinuity=Esee=xPI=QI=TI=UI=Vz=and=xNMzFK=fn=the=present=workI=the=following==was=assumedW==

=OO

÷÷ø

öççè

æ+÷÷

ø

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æ=

tc

t

nc

neff w

wwww = EOF=

=where=wn=is=the=mutual=displacement=component=normal=to=the=interface=and=wt=the=tangential=oneK=wnc=and=wtc=are=the=related=critical=valuesK=

SPO=

ff= weff=[ =N =no =stress =transfer =occurs =and =the =crack =is =therefore =stress =freeI =otherwiseI =the =stresses =are =decreasing= functions= of= weff= that= follow= a= preJdefined= softening= lawK= fn= the= present= work= the=above=mentioned=law=is=assumed=as=follows=Esee=xNPzFW==

= ( )( ) ú

û

ùêë

é--

×---==

aa

tt

ss

expNexpN

NMM

effw = EPF=

=there=it=is=assumed=α=Z=RK=qhe=point=where=is=weff==Z=N=is=called=real crack tipK==qhe=behaviour=of=the=material=outside=the=cmw=is=linear=elasticK=fn=a=symmetric= modelI= it= is= well=known=that= the=fracture=process=starts=symmetricallyI=but= loses= this=property =afterwards =Esee =xRzI =xNNz =and =xNOzFK =fn =order =to =numerically =simulate =this =experimental =evidenceI=a=realistic=scatter=in=strength=was=assumedI=as=shown=in=qable=NK==

Table N=fnterface=parameters==

= ft kLmmO=

fs kLmmO=

wnc mm=

wtc mm=

=left=side=

=MKOQO=

=MKPSN=

=MKR=

=MKR=

right=side= MKOPP= MKPRN= MKR= MKR==

qhereforeI==collapse=is=determined=by=a=deJbonding=process=that=occurs=on==the=right=EweakerF=sideK=qable=O=shows=the=assumed=elastic=propertiesK==

Table O=blastic=properties==

= voung’s=module=kLmmO=

moisson=ratio=–=

jortar= QPUM= MKNR=ptone= OQMMM= MKOM=

==qhe=numerical=analyses=were=executed=using=the=ABAnrp=xSz==code=by=applying=a=preJdefined=downward=velocity=to=the=upper=face=of=the=stone=blockK=qhe=deformed=finite=element=mesh=is=shown=in=cigKTK==

==

FigK T cinite=element=mesh=at=the=maximum=loadK=qhe=displacements=have=been=enlarged=NMM=timesK=

SPP=

4K bXPbRIMbNTAi ANa NUMbRICAi RbSUiTS =

A=preliminary=elastic=analysis=shows=four=stress=singularity==pointsW=two=notch=tips=at==the=specimen=topI=and=two=at==the=specimen=bottom=Esee=cigK=OFK=cour=cohesive=cracks=start=to=propagate=from==this=pointsI=along=the=biJmaterial=interfacesI=which=are=the=weakest=planes=involved=in=the=singular=stress=fieldsK==Because =of =the =wedges =Esee =cigK =TFI =the =cracks =that =start =from =the =bottomI =of =the =specimen =show =a=greater=velocity=than=the=cracks=that=start=from=the=top=of=the=specimenK=qhereforeI=the=second=couple=of=cracks=plays=the=role=of=the=main=cracksK=qhe=surface=treatment=shown=in=cigK=O=increases=the=values=of=wnc=and=wtc= in =comparison=to=the=case=of =the=interface=between=the=same=type=of =mortar =and=brick=discussed=in=xNOzK=qherefore=I=the=loss=of=symmetry=no=longer=occurs=at=peak=loadI=but==at=the=end=of=the=softening=phase=and=it=causes=the=specimen=to=collapseK=cigK=U=shows=that=the=teflon=sheetI=inserted=at=the=contact=surface=between=the=upper=and=lower=wedgeI=is= able= to= reduce= the= friction= and= therefore= also= = the= load= valuesK= qhe= friction= is= disregarded= in= the=numerical=simulationK=qhe=numerical=and=experimental=results=are=in=good=agreementK==

==

FigK U sertical=load=sp=horizontal=displacementW=E○F=kumerical=solution=I=E□F=ppecimen=N=without=qeflonI==E F=ppecimen=O=with=qeflon==

=Table P=jaximum=values=of=the=load=and=displacement=

=

= jax=load= jax=mortar=–toJmortar==horizontal=displacement=

= k= mm=specimen=N=Ewithout=qeflonF= PRSR= MKQOUR=specimen=O=Ewith=qeflonF= OPOM= MKQOST=numK=simulation= OUON= MKQMMN=

=RK ClNCiUSIlNS

– An=innovative=preliminary=design=stage=laboratory=procedure=for=the=preJqualification=of=repair=mortars=applied=to=historical=masonry=buildings=has=been=describedK==

– qhe= evolutionary= phenomena= involved= in= the= deJbonding= process= of= mortar= in= a= coupled=stone= block= –= mortar= system= have= been= accurately= analyzed= by= means= of= the= proposed=experimental=setupK==

SPQ=

– ft= has= been= possibleI= through= the= cohesive= crack= modelI= to= theoretically= interpret= the= above=mentioned=phenomena=that=occurs=at=the=interface=between==stone=block=and=mortarK=

– qhe= mechanical= behavior= of= the= interface= has= therefore= been= characterizedK= qhe= obtained= =parameters==can=be=used==to=analyse=a=problem=with=different=boundary=conditionsK=

ACKNlWibaGbMbNTS =qhe= nancial= support= provided= by= the= miedmont= oegion= through= the= obJcobpClp= project= is=gratefully=acknowledgedK===RbFbRbNCbS

=xNz Bocca=mKI=drazzini=AK= EOMNOF=bxperimental=procedure=for= the=preJqualification=of=strengthneing=

mortarsK=fnternational gournal of Architectural eeritage=SEPFW=PMOJPONK=xOz drazzini=AK=EOMMSF=bxperimental=techniques=for=the=evaluation=of=the=durability=of=strengthening=

works=on=historical=masonryK=Masonry fnternational=NVW=NNPJNOSK=xPz Cervenka =g =hishen =g =j =C =and =paouma =s =bK =jixed =mode =fracture =of =cementious =bimaterial =

interfaces;=part=iiW=kumerical=simulationsI=bngineering cracture Mechanics=NVVU;=SMW=VRJNMTK=xQz Barpi=cK=and=salente=pK=qhe=cohesive=frictional=crack=model=applied=to=the=analysis=of=the=damJ

foundation=jointI=bngineering cracture Mechanics=OMNM;=TTW=ONUOJONVNK=xRz Barpi= cK= and= salente= pK= pizeJeffects= induced= bifurcation= phenomena= during= multiple= cohesive=

crack=propagationK=fnternational gournal of polids and ptructures=NVVUI=PRENSFW=NURNJNUSNK=xSz aassault=pystem=pimulia=CorpKI=mrovidenceI=ofI=ABAnrpI=release=SKNMI=OMNMK=xTz Barpi =cK =and =salente =pK =cuzzy =parameters =analysis =of =timeJdependent =fracture =of =concrete =dam=

modelsI=fnternational gournal of kumerical and Analytical Method in deomechanics I OMMO=OSW=NMMRJNMOTK==

xUz Barpi= cK= and= salente= pK= = A= fractional= order= rate= approach= for= modeling= concrete= structures=subjected= to= creep= and= fractureI= fnternational gournal of polids and ptructuresI= OMMQI= QNLVJNMW=OSMTJOSONK=

xVz Barpi= cK= and= salente= pK= = iifetime= evaluation= of= concrete= structures= under= sustained= postJpeak=loadingI bngineering cracture MechanicsI=OMMR;=TOW=OQOTJOQQPK=

xNMz Barpi= cK= and= salente= pK= = jodeling= water= penetration= at= damJfoundation= jointI bngineering cracture MechanicsI=OMMUITRLPJQW=SOVJSQO;=NMKNMNSLjKengfracmechK=OMMTKMOKMMUK=

xNNz Alberto= AKI= Antonaci= mKI= salente= pK= aamage= analysis= of= brickJtoJmortar= interfacesINNth fnternational Conference on the Mechanical Behavior of MaterialsI=ppK=NNRNJNNRSK==

xNOz Bocca= mKI= drazzini= AKI= jasera= aKI= Alberto= AKIsalente= pK= = jechanical= interaction= between=historical=brick=and=repair=mortarW=experimental=and=numerical=testsI=gournal of mhysicsI OMNN=volK=PMR=nK=NK=–=fppk=NTQOJSRUUK=

xNPz eKAKtK=Cornelissen=and=aKAK=eordijk=and=eKtK=oeinhardt=bxperimental=determination=of=crack=softening=characteristics=of==normal=and=lightweight=concreteI=eeronI=NVUSI==PNW=QRJRSK=

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