High performance fibre reinforced cementitious composites: Six memos for the XXI century societal and economical challenges of civil engineering

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Case

study

High

performance

ﬁbre

reinforced

cementitious

composites:

Six

memos

for

the

XXI

century

societal

and

economical

challenges

of

civil

engineering

Liberato

Ferrara

DepartmentofCivilandEnvironmentalEngineering,PolitecnicodiMilano,Italy

ARTICLE INFO

Articlehistory:

Received26November2018

Receivedinrevisedform10January2019

Accepted10January2019

Keywords:

Highperformanceﬁbrereinforced

cementitiouscomposites Lightness Quickness Exactitude Multiplicity Visibility Consistency ABSTRACT

Worldwideincreasingconsciousnessforsustainableuseofnaturalresourceshasmade “overcomingtheapparentcontradictoryrequirementsofcostandperformance effective-nessachallengingtask”aswellasamajorconcern.HighPerformanceFibreReinforced CementitiousComposites,byprovidingtailoredandmultiplefunctionalizedperformance canrepresentanassetfortheconstructionindustrytofacethechallengesimposedbythe needsofourcontinuouslyandfastevolvingsociety.Thepaper,movingfromaparallelwith “Sixmemosfromthenextmillennium”byItaloCalvino,theauthorwillprovidehisown perspectiveonthecurrentstateonthetopic,tryingtohighlightthebeneﬁtsachievable throughareliableandconsistentincorporationintoadesignandconstructionpracticefor bothnewandexistingbuildingsandstructures.

1.Introduction

Theconstructionindustry,whichaccountsforabout6%ofglobalGDP(from5%indevelopedcountriesupto8%in developingones)iscalledtoplayasigniﬁcantroletowardsasustainableandinclusiveglobalworldwidegrowth,money investedintheinfrastructuresectorbeingexpectedtofeatureaKeynesianmultiplierequalto1.5[1,2].Thisisalsoduetothe peculiarfeatureofconstructionindustry,which,withtotalannualrevenuesofabout10trillionUSDand3.6trillionUSD addedvaluesandmorethan100millionpeopledirectlyemployedworldwide,servesalltheindustryverticals.Actually38% ofglobalconstructionvolumeaccountedforbyresidentialhousing,32%bytransport,energyandwaterinfrastructures,18% by institutional and commercial buildings and 13% by industrial sites. With such ﬁgures, it is no surprise that the constructionindustryisnotonlythesinglelargestglobalconsumerofresourcesandrawmaterialsbutalsooneofthelargest generatorsofsolidwasteaswell,with,e.g.,about40%ofsolidwasteintheUSand35%inEU28countries(Eurostat2014 estimate)beingproducedbyconstructionanddemolitionactivities[1].

Withabout10billiontons(correspondingtoabout4billioncubicmeters)producedeachyear,whicharelargerthanthe totalofallotherbuildingmaterials,includingsteel,wood,aluminiumandplastic,concreteisthemainactorofthewhole constructionindustry.Itsproductionandconsumptionfeedsthedemandforalikewisehighproductionandconsumptionof themainconstituentsofconcrete,includingcement(morethan4blnt/y),aggregates(about48blnt/y)andwater,thelatter representingahighlysensitivesocietalissue,competingwiththeaccesstowaterneedsoftheworldpopulation.

Itwouldbeanywaydeceptiveandmisleadingtolimitoneselftothesegrossﬁguresasanindicatorofthe“sustainability” ofconcreteasaconstructionmaterial,mostofallwithreferencetoitscarbonfootprint.Asamatteroffact,“thereason concretehasahighfootprintasawholeisthattherearejustsuchhugeconcretequantitiesused”,andthereasonforwhichit isusedinsuchlargeamountsand“hasbeenusedin[...]pioneeringarchitecturalfeatsformillennia”isthat“itis,simply,a

https://doi.org/10.1016/j.cscm.2019.e00219

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CaseStudiesinConstructionMaterialsxxx(2018)xxx–xxx

ContentslistsavailableatScienceDirect

Case

Studies

in

Construction

Materials

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remarkablygoodbuildingmaterial”and“isinfactaverylowimpactmaterial”[3].Moreover,“ifyoureplaceconcretewith anothermaterial,itwouldhaveabiggercarbonfootprint”[3].This,besidesthegoodperformanceofconcreteintermsof, among the others, compressive strength, thermal inertia and cost effectiveness, is mainly due the worldwide local availabilityofitsrawconstituents.

Theaforementionedenvironmentalfootprintofaconstructionmaterialisonlyoneaspectofthe“sustainability”ofthe engineeringapplicationemployingthat samematerial,beingiteithera structuralelementorsubassembly,abuilding structureoraninfrastructureunitornetwork.

Withtheaimofprovidingaquantitativemeasureofthe“sustainabilityindex”ofaconstructionmaterialand/orofany kindofengineeringapplicationmadewithit,twomethodshavebeenrecentlyproposed,whichdeﬁneeitheraSustainability PotentialIndex[4]oranA(pathy)Index[5]:

SUSTAINABILITYPOTENTIALINDEX¼ ServiceLifePerformance

Environmentalfootprint ð1Þ

AðPATHYÞINDEX¼ Environmentalf_Perf_ormanceootprint ð2Þ thelatterbeingobviouslylowerinthecaseofabetterperformingsolution.

Bothindicesencompassthethreetraditionalpillarsofsustainability,namelytheenvironmentalaspects,throughthe environmentalfootprint,andthesocialandeconomicones,throughtheperformanceandservicelifeconsiderations,thus incorporatingintoaunique“decisionmakingtool”informationconcerningimpactresultingfromtheproductionofbuilding materials,theerectionofbuildingsandstructuresandthesubsequentusethereof.

Withtheaimofprovidingaconcreteansweringtothesustainabilitychallenges,theconcreteindustryinthelastdecades hasbeenintensivelyworkingtothedevelopmentanduseofanewbroadcategoryofadvancedcementbasedmaterials, namelyHighPerformanceFibreReinforcedCementitiousComposites(HPFRCCs),whichareabletoprovidetailoredand multiplefunctionalizedperformancewhich canrepresentanassetfortheconstructionindustrytofacethechallenges imposedbytheneedsofourcontinuouslyandfastevolvingsociety.

Whilenotenteringintospeciﬁcquantitativeassessmentofanyofthemultiplesolutionsprovidedbytheresearchandin severalcasesalreadyavailableonthemarket,thepaper,throughanoverviewofwhathasbeencurrentlydonetoimproveto sustainabilityperformance ofconcretematerialsandstructuresbyactingoneitheroneortheotherfactoroftheafore deﬁnedindices,alsowantstoprovideamodestcontributiontodispelthemythoftheconstructionindustryasasector traditionally regarded as highly inertial in implementing innovation. Through this, without any presumption to be exhaustive,thepaperwillprovidetheauthor’spersonalperspectiveonthetopic.Thisperspectiveventuresintoaparallel withtheSixmemosforthenextmillennium1_,_a_series_of_six_lectures_that_the_Italian_writer_Italo_Calvino_was_expected_to_deliver

fortheCharlesEliotNortonLecturesatHarvard,whichheneverdidbecauseofhisprematuredeath.Thelectures,whichbut thelastonewerereadyatthetimeofCalvino’sdeathandwerepublishedinaposthumousbook,addressedthevalues (memos)of literaturethat Calvinofeltwereimportantforthecomingmillennium,i.e. Lightness,Quickness, Exactitude, Visibility,Multiplicity.AllthatisknownofthesixthlectureisthatitwastobeonConsistency.Thesesixmemoswillbetakenas areferencetohighlight,stillfromtheauthor’spersonalpointofview,themostexcitingchallengesthatthecivilengineering communitycanfacethroughareliableandconsistentincorporationofadvancedcementbasedmaterialsconcepts and performancesintodesignandconstructionpracticeforbothnewandexistingstructures.

2.Reducingtheenvironmentalfootprintofconcreteandcement-basedmaterialsandstructures

Efﬁcientreductionoftheenvironmentalfootprintofconcreteandcementbasedmaterialsandstructurescanbeachieved throughcombinedactionaimed,ontheonehand,atusingmaterialswithareducedfootprintthemselvesand,ontheother, tothedevelopmentof“environmentally”friendlymaterialandstructureconcept,productionandconstructiontechniques. In sucha framework, theproduction of cement,as a primary constituent of concrete, plays a role of paramount importance,alsoconsideringitrequireslargequantitiesofrawmaterials(approximatelyabout2tonsoflimestoneandshale, whereavailable,pertonofcement),andhighenergy(about4GJpertonofcement)andproducesabout1tonCO2pertonof

cement.Thismakesthecementindustryresponsibleofabout5%notenergyrelatedgreenhousegasemissionsworldwide. Itwellworthremarkingthatbothcementandconcreteindustryarereallymakinggiantleapsforwardinimprovingtheir sustainabilitysignaturethroughthereductionofenvironmentalfootprintofcementproduction.Theadoptedmeasures rangefromoptimizationofcementproductionprocesses,including,e.g.,reuseofwasteheatoruseofsecondaryfuelssuchas waste tires in cement kilns. Moreover, formidable research and progresses in concrete technology have promoted a tremendousoptimizationintheuseofcementandbinders.AshighlightedbyDaminelietal[6],abinderconsumptionper unitstrengthofconcreteaslowas5kg/[m3MPa]isnowadayspossible,thankstomix-designconceptsbasedonoptimum

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particlepackingmodelsaswellastothedevelopmentanduseoftailoredadmixtures.Moreover,theconstanteffortsinthe reductionofcementdemandfortheproductionofconcrete,the“performances”ofinterestholdingthesame,haslong resultedintoconsolidateduseofsupplementarycementitiousmaterialsasreplacementofcementinconcreteandinthe productionofmulti-blendedcements,includingflyash,groundgranulatedblastslag,silicafume,naturalpozzolansand by-products from a range of industrial and wastereclaiming/combustion processes [7]. Though expectedto undergo a compoundannualgrowthrateofabout6%inthecoming_fivetosevenyears[8],themarketofsupplementarycementitious materials,whoselargestshareiscurrentlydetainedbyflyashes,willhavetofaceinthenextshorttomediumtermfuturethe progressiveshiftingofpowerproductionfromfossilfuelsources,whichareoneofthemajorsourcesofSCMs,toalternative onesaswellasoftheproductionofsteelfromoretoscrap.

Researchonalternativebinders,whoseusemaycontributetoafurtherreductioninthedemandofPortlandcementand henceintheresultinguseresourcedepletionandenvironmentalfootprint,including,e.g.,CalciumSulfo-Aluminatecements [9],AlkaliActivatedMaterials[10]andLimestoneCalcinedClayCements(LC3)[11,12].Themarketpenetrationofthesenew potentiallyattractivetechnologieshasanyway,ontheonehand,tocopewiththegeographicalproximityofsupplychainof precursors,whichisoneofthemostformidableadvantagesofPortlandCementtechnology.Insomespeciﬁccases,the competitionwithotherwelldevelopedindustrialsectors,suchasthealuminiumindustryinthecaseofCSAcements,has alsotobeconsidered.Ontheotherhand,ithastoberemarkedthatalltheexistingstandardsonconcretematerialsand productsandconcretestructuraldesigncodeshaveacascadingdependenceontheassumptionthatPortlandCementisthe mainconcreteconstituent,eveninthepresenceofsupplementarycementitiousmaterials.

Thesesamestatementsholdtrueinthecaseofreplacingnaturalaggregateswithrecycledonesobtained,e.g.,from constructionanddemolitionand/orotherkindsofwastesorinthelikewiseinterestingcase ofemployingasdispersed reinforcementfibresobtained,e.g.,fromscraptires,wastePETbottlesornaturalvegetableonesfromfoodandagriculture industryresiduals[13].Inallthelatteraforementionedcasesthedifferentpropertiesofarecycledconstituentfromanatural (inthecaseofaggregates)orindustriallyproducedone(inthecaseoffibres)havealsotobecarefullyconsidered.Thissurely refers to the regularity and constancy of the physical, chemical and mechanical properties of the aforementioned constituentsand,evenmoreimportantly,totherelationbetweenthemicrostructuredevelopmentandcharacteristicsand itslinkwiththemacroscopicpropertiesofthecementitiouscomposite,whichmayevensignificantlydifferfromtheoneson whichstructuraldesigncodesarebasedorimplicitlyrelyupon.

Lastbutnottheleasttheissueofwaterhastobeconsidered.Asamatteroffact,theprescriptioncontainedinstandards andstructuraldesigncodesworldwidereferringtothealmostexclusiveuseofpotablewaterforconcreteproductionmay enterintonotseldomdramaticconﬂictwiththewaterneedsofafastgrowingpopulationmainlyin,butnotexclusively, areasaffectedbypermanentscarcityofwaterand/ordroughts.Inthisrespect,theusenotonlyofwaterresultingfrom washingoutconcretemixingequipmentbutalsooftreatedwastewaterandevenseawaterinthemix-designmaybe deemedasconditionallypossible,ifnotfullylegitimized[14].

Whendesigningandbuildinganengineeringand/orarchitecturalfeat,the“sustainabilitysignature”oftheemployed material(s)hasalsotobeanalysedinthesightoftheirstructuraluse.Asamatteroffact,ahigherlevelofperformancecan allow,e.g.,fortheuseofreducedquantitiesofagivenmaterial,the“sustainabilitysignature”oftheﬁnalapplicationhaving thustotakeintoaccountnotonlythesignatureofthematerialbutalsoitsusedvolume.Moreover,abetterperformancecan alsoimplyreducedmaintenanceneeds,which,allalongtheservicelifeofthebuildingand/orstructure,doalsocontributeto theoverallsustainabilitysignature.Theadventonthemarketofadvancedmaterialsinastartingphaseisoftenaccompanied bythesimpleimprovementofexistingstructuralconceptsandconstructiontechniques.Though,ifthematerialaimsto represent a breakthrough in the construction industry, thedevelopment of new advanced construction technologies implementedintosuitablylikewiseinnovativetailoredstructureconcept,designandanalysisprocedure,whichhavealsoto consistently incorporate the life-cycle assessment of the performance, in a cradle-to-grave or even cradle-to-cradle approach,thusalsoaddressingissuesrelatedtotherecyclabilityoftheemployedmaterials.

3.Whatperformanceforwhatscenario?HighPerformanceFibreReinforcedCementitiousCompositespushingahead theboundariesofstructuralconcreteconcept

Athoroughevaluationofthesustainabilityofaconstructionwork,intheframeworkofthebuiltenvironmentasawhole, hastoconsidertheperformanceoftheconstructioninserviceconditionsallalongitslifecycle,includingitsdurability, whichis,asoftoday, oneofthemajorconcerns,ifnotthemostdramaticallyseriousone,oftheconstructionindustry. Reinforcedconcretestructuresmoreandmorefrequentlyexhibitearlierandfasterandmoreandmoreseveredecayoftheir levelofperformanceintheservicescenariosandconditionstheyhavebeensupposedlydesignedfor.

Thoughacomprehensiveanalysisofthecausesoftheaforementionedproblemissofarlacking,severalissuescanbe called for to justify the somewhat premature decay of structural performance and anyway their higher durability sensitiveness,including,e.g.:

-currentconstructiontechnologies,qualiﬁcationoftheworkmanshipandinsomecasesthesamestructureconcepthave not adequatelypaced upwiththedevelopment in materialconcept and technology ofconcrete and cement-based materials;

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- climatechangeandenvironmentpollutionissues,whichaccompanyalsoaprogressivelyincreasingurbanizationofthe worldpopulation,togetherwiththefactthatthematerialanddesignconcepttogetherhavepushedaheadtheservice stressboundaries,aregoingtothreatenmoreseverelythematerial,wheninserviceinthestructure[15].

Concreteisexpectedtocrackbecauseofitsinherentbrittlenessandlowtensilestrength;forthisreason,itisgenerally usedincombinationwith,prevalentlysteel,reinforcement,whichtakesthetensileforcesgeneratedbytheappliedactions. Cracksopenaningresspathwayforaggressiveagentstopenetrateinsideastructuralelement,reachingthereinforcement andtheinsidebulkconcrete,andactivatingcomplexdegradationmechanisms,amongwhichthecorrosionofthesame reinforcementissurelyamongthemostthreateningones.Unexpectedand/ornotcorrectlypredicteddecayofthestructural performanceresultsintounpredictedmaintenance needswhich, besides beingcostlier thanifcorrectlypredicted and planned,hardlycanrestorethepristinelevelofperformance,thusimplyingalsoanincreasedfrequencyofthesubsequent followingmaintenanceactionsandanuncontrolledgrowthofthelifecyclecosts.Recentestimateshaveshownthat,e.g.,the costofrepairingcorrosiondamages(includingalsoautomotiveandaircraftindustry)sumsuptoabout3.5%oftheworldGDP [16]andthatcurrentlyrepresentsasigniﬁcantshareoftheyearbudgetofconstructionindustryindevelopedcountries accountsformaintenanceandrepairofexistingstructures.Atthesametime,thelifespanofthesamemaintenanceand repairworksisdramaticallyshortening,asfromacasehistoryanalysisrecentlyprovidedbytheCON-REP-NETproject[17], whichhasshownthat50%oftherepairedconcreteworksfailedagain,25%ofwhich intheﬁrst5yearsafterrepair.A percentagesharewhichincreasesto75%and95%respectivelyifthetimeobservationframeisextendedto10and15years aftertherepair.

Atrue“durabilitybased”designapproachisactuallyfarfrombeingformulatedincurrentdesigncodes,thoughitis appropriatelyrecognizedthattheachievementoftherequireddurabilityisthecomplexoutcomeofthesuitablechoiceof structureconceptandshape,materialselection,aswellasoftheenforcementof“operational”designcriteria,whichlimit thecrackwidthundertheanticipatedactionstosuitablescenario-basedthresholdvalues[18,19].Limitationofcrackwidth beinghencerecognizedasthemajorrequisitefortheintendeddurability,concretetechnologyhasdeveloped,overthepast fiftyyears,FibreReinforcedConcrete(FRC).Thankstothedispersedfibrereinforcement,aneffectivecontrolofcrackwidth canbeachievedthroughouttheentirestructureandstartingfromtheveryearlyages.Asamatteroffact,becauseoftheir wire-likefeatures,fibresareabletointeractwithcracksmuchfinerthanwhatobtainablewiththesmallestcommercially availablebardiameters[20].Theboundariesofthisconcepthavebeenpushedforwarduptotheformulationoftheso-called HighPerformanceFibreReinforcedCementitiousComposites(HPFRCCs),whosecompositionisdesignedthrough micro-mechanicalconceptsbasedonfibrepull-outandcracktiptoughnessbalance.Thankstothis,aftertheformationofafirst crack,fibreseffectivelyprovideathroughcrackstressredistributionwhichenablesnewmultiplecrackstobeformedwhile controllingtheopeningofthepreviouslyformedones,whicharebasicallystoppedfromfurtherwidening,uptotheunstable localizationofonemajorcrack.Thismakesthematerialableto“spread”theentityofasingledamage(crack)intoaseriesof tightlyspacesandnarrowlyopenedmultiplecracks,whosesinglewidthishencemuchlessdetrimentaltothestructural durability[21].

TheHPFRCCconceptisrootedintothosewhichcanbeconsideredthethreemajorinnovationsinthefieldofconcrete technologyinthesecondhalfoftwentiethcentury,namely,besidesFibreReinforcedConcreteasrecalledabove,datingback totheearlysixties,Self-CompactingConcrete,datingback,alsothroughsomeprecursors,tothelateseventiesandearly eighties[22],andHighPerformanceConcrete,alsogoingbacktosomepioneerideasputforwardbetweentheseventiesand theeightiesofthelastcentury[23].Thecombinationoftheperformancebenefitsofthethreetechnologiesintoaunique material,besides thewell-known advantagesin terms ofmore efficient and worker-friendlyconcrete production and application[24],resultsintoone-of-a-kindfeatures,anideaofwhichwillbeprovidedintheforthcomingsection,which makeHPFRCCsavaluableassetfortheconstructionandcivilengineeringsectortofacethechallengesofthesocietaland economicneedsofXXIcentury.

4.HighperformanceﬁbrereinforcedcementitiouscompositesperformingCalvino’ssixmemosforthenext millennium

4.1.Lightness

Committing to a sustainable built environment implies the “namesake” goal of “lightening” the burden on the environment by theactivities related to theproduction, useand disposalof construction materialsand engineering buildings,structuresandinfrastructures.

Theeffectivenessoftheeffortsceaselesslylavishedonimprovingthecompressivestrengthyieldbybindershavebeen alreadyrecalledabove[6].Though,focusingonlyonthematerialcompressivestrengthmaybelimitingifnotmisleading sinceitisthestructureconceptandtheresultingstructuraluseofthematerialwhichgovernshowmuchoftheachievedand potentially“in-structure”availablecompressivestrengthisactuallyusedandexploited.

Inclassical“beam”elementssuchshareislimitedbythetensileperformanceofthematerial,becauseoftheneedof sectionalforceequilibrium.Inthisrespect,ratherthanthethree-digitscompressivestrengthofHPFRCCs,itistheirsignature tensilebehaviour,featuringalmostconstantloadbearingcapacityuptosigniﬁcantstrainlevels(strain-hardening)that enablesaremarkabletensilestressredistributioncapacityoverthecrosssection.Thismakesitpossible,evencontinuingto

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adoptclassicalbeamelementsmainlyworkinginbending,tosignificantlyreducethedepthofstructuralelements,holding theloadbearingcapacityconstant.Moreover,sincethedispersedfibrereinforcementmayevencompletelyreplacethe conventional reinforcement in few speci_fic applications,the depthof the elementis not even longer constrained by durability-relatedminimumcoverthicknessrequirementsdictatedbytheneedtoprovideadequateprotectiontothesteel bars(SeeFig.1).

InFig.2aatypicalapplicationisshown,asproposedin[25],where,intheroof-deckarrangementofaprecastreinforced concretebuilding,an80mmthickreinforcedconcreteslab,deemedtosupportitsself-weightand,incase,snowload,canbe effectivelyreplaced,asalsoconﬁrmedbyexperimentaltests(Fig.2b)bya25mmthickHPFRCCslab(theemployedHPFRCC mixcompositionisprovidedintheinsetTable).Theresultingabout70%weightreductiondoesnotonlycompensateforthe highdosageofcementandbinderinthebulk“percubicmeter”compositionaswellasfortheexpectablehigher“percubic meter”costofthematerial(50%ofwhichisduetothebinders,35%totheﬁbres,10%totheadmixture,sandandwater accountingfortherest).Thisonlyconsideringthe“materialdelivery”costanddeliberatelyomittingtoconsideraspects relatedtoitsdurability,whichwillbedealtwithlater.

Such a remarkable “lightening”wouldalsoimply benefitsonthedesign oftheunderneath supportingcolumnand foundationstructure,toanevenmoresignificantextentifthedesignincaseofearthquakehastobeperformed,alargermasson thetopanditscorrespondinglyhigherearthquakeinducedinertiaforceresultingintoahigherbendingmomentatthebaseof thecolumnsandotherlateralloadresistingelements.Lastbutnottheleast,thereducedelementthicknesswouldallowalsoan optimizationofthetransportandhandlingoperationandcosts,thesametruckbeingabletotransportthreetimesasmuchthe numberofroofslabsthaninthecaseofthetraditionalreinforcementsolution.Thiswouldnotonlyallowafasterconstruction, alsothroughreducednumberofcraneswithevenlowerliftingcapacity,butalsobringafurthercontributiontotheoverall sustainabilitysignatureofthewholeconstructionprocess,e.g.throughreducedimpactontrafficandfuelconsumption. 4.2.Quickness

Theaforementionedconsiderationsaboutthehigherefficiencyoftheconstructionprocessthatcanbeachievedthankstothe use, mainly - evenifnot exclusively -in precastconstruction industry, ofHPFRCCs brings us into the secondmemo.Thecomposition ofHPFRCCs,resultingfromthemicro-mechanicallybaseddesignrecalledabovetargetedtoachievestrain-hardeningtensile behaviour,ischaracterized,asalsoobservablefromtheinsetTableinFig.2b,byahighcontentofbinder,verylowmaximum aggregatesizeandhighdosageofsuperplasticizer,tobalanceouttheeffectsofthelikewiserequiredhighdosageoffibresandlow watercontent.Thissamecompositionishighlyconducingtoendowingthematerialwithasuperiorperformance(Fig.3)inthe fresh state, implementing the latin "Festina lente”(makehasteslowly) motto throughanadaptedrheology characterizedby alow yieldstress,forenhanced_flowabilityandself-levellingcapacity,andabalancedviscosity,instrumentalatguaranteeingan adequateresistancetostaticanddynamicsegregationofaggregatesandmostofallofthefibres[24,26–29].

4.3.Exactitude

Asaddressedabove,oneoftheadvantagesofincorporatingﬁbresintoamatrixwithadaptedrheologyistheachievement ofauniformdispersionofﬁbreswithinstructuralelements,notevenaffectedbytheirsegregation[26–29].Thisrequisiteis

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ofparamountimportancefor a reliablestructuralperformance ofelementsmadewithFibreReinforced Concreteand CementitiousComposites.

Asuitablyadaptedrheology,i.e.anadequatelybalancedperformanceofthefluidmixtureasabove,couldalsoimplythe possibilityofeffectivelyaligningthefibresalongthecasting-flowdirection[28,30–34].Thispreferredorientationoffibersis duetotwoconcurrentcauses:1)theprofile ofthedragforcesinduced bytheflowand 2)thewalleffect[35].Flows dominatedbyshearstressesfeatureaparabolicflow-velocitycrossprofileswithanassociateddistributionofdragforces (Fig.4).Thisalignmentcanbepracticallyconsidered,attheindustrialscale,asanalmostinstantaneousphenomenon,since itoccursina“maximumfiberorientationcharacteristictime”whichisoftheorderofacoupleseconds,whichisfarshorter thanthedurationofanyrealcastingprocess[35].Thesecondcauseforpreferredalignmentoffibersisthesocalled“wall effect”,sinceitis“notpossibletofindafiberperpendiculartoawallatadistancelowerthanhalfthelengthofthefiber”[35]. Bysuitablytailoringthecastingprocesstotheintended application,i.e. combiningComputational FluidDynamics modellingofthecastingprocess[36_–40]withclassical_finiteelementstructuralanalysis,the_flowdirectionofthefresh

Fig.2.(a)traditionalprecastroofdeckarrangement(left)vsHPFRCCone(right);and(b)experimentaltestingtheloadbearingcapacityoftheHPFRCC

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concrete,alongwhichfibrestendtobealigned,canbemadetocoincide,ascloselyaspossible,withtheanticipatedstress pattern(i.e.,thedirectionofprincipaltensilestresses)withinthestructuralelementwheninservice.Thefibre-alignment dependantmaterialbehaviour(Fig.5)canbeexploitedthroughabetterstructuralef_ficiencyfurthercontributiontothe elementsizeandstructureoptimization[25].

Fig.3.adaptingtherheologyofFRCCs(a–b)forenhancedﬁbredispersion(c)[24].

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Fig.5.Aligningthefibresperpendicularly(a)andparallel(b)totheflowandtoprincipaltensilestressesinbeamspecimens;respectiveresultingdeflection

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4.4.Multiplicity

Theadventandimplementationofnanotechnologyintheconstruction_ﬁeld,whichisgoingtoenableametamaterial conceptapproachtoconstructionmaterialswhich,throughthemanipulationofthemostinnerstructureofthematerial wouldallowtoobtainpropertiesand/orlevelsofperformancewhichcouldnotbeobtainedandachievedthroughtraditional processing[41].

ExamplesofresearchinthisﬁeldrangefromtheuncouplingbetweencompressivestrengthandYoungmodulus[42],a topicofextremelyhighinterestintheconstructionofhighrisebuildings,tothepossibilityofendowingconcretewith self-sensing[43]orself-curing[44]properties,through,e.g.,therespectiveuseofcarbonandcellulosenano-constituents,tothe functionalizationofﬁbre-matrixinterfacefortailoredenhancementofthematerialperformance.

AmongthemultiplicityofperformancethattheHPFRCCsareabletoprovide,itisworthrecallingthatthesynergybetween “extreme” crackwidthcontrol andmaterialcomposition, asdescribedabove,alsoresultsintoa high conducivenessto autogenousself-healing(Fig.6),withsynergeticeffectsontheenhancementofthematerialandstructuraldurability[45,46].

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As a matter of fact, the matrix is able, on the one hand,throughits extremelyhigh compactnessand crackcontrolling ability, to slowdown thepenetrationof aggressiveagentsintoitscorestructure, andeventuallyto thelevel ofthereinforcement.Thanksto itsinbornself-healingcapacity,thematrixisalsoabletoprogressivelysealthesametightlyspacedandnarrowopenedcracks, thusdrawingtowardsarecoveryofitspristinelevelofperformanceintheun-crackedstate.Thecompositionofthiscategoryof advancedcementitiouscompositesfeatureshighcontentsofcementandsupplementarybinders,witheitherpozzolanic(ﬂy ash,silicafume)ordelayedcementitiousactivity(slag)andlowwatercontent.Theresultinghighamountofreactivematerial whichremainsun-hydratedandentrappedinsidethebulkvolumeofastructuralelementmaybe,uponcrackingexposedto outdoorenvironment,incasefeaturingpresenceofliquidorvapourwater.Thesecanbothactivatedelayedhydrationreactions aswellascarbonationones,whoseproductsprecipitateontothecracksurfacessealingit.

Moreover,healingproducts,besidesreconstructingthethrough-crackmatrixcontinuity,arealsolikelytoimprovethe ﬁbre-matrixbond.Itisfurthermoreworthremarkingthatthepresenceoftheﬁbresandthesignaturetensilebehaviourof thematerialmaketheaforementionedrecoveryofthepristinelevelofperformancereferredtotheun-crackedstatetruefor bothdurabilityandmechanicalproperties.Thismayalsoresult,uponreloadingahealedspecimen,intotheformationofnew cracks,farfromthehealedone,insteadofthere-openingofthelatter(Fig.7)[47].

Self-healingmaterialsarewellknownintheﬁeldofbiology.Bloodclotting,skinwoundhealingandbonereconstruction are _{“sparkling”} examples of self-healing functionalities inborn in biological materials which material science has successfullyattemptedtoincorporatealsoinman-madeones,including,amongtheothers,polymers,metals,asphalts, paintingsandcement-basedconstructionmaterialsaswell[48].Itisblatantlyundeniablethatthepossibilityofengineering orstimulatingtheself-repairing functionalitiesin cement-basedmaterialswould enhancethematerialand structural durabilityalsoresultinginreducedmaintenanceneedsoveranextendedstructureservicelife.

Inthewholeframeworkhereinoutlinedself-healingcement-basedmaterialswouldhencerepresentanexceptionalasset forshapingthesustainabilityofthecement,concreteandconstructionindustry[46].Theauthorhasintensivelyparticipated intoresearchrelatedtostimulatedhealingthroughcrystallineadmixtures,wellknownandwidelyemployedinmodern concretetechnology,beingclassifiedasaspecialtypeofpermeabilityreducingadmixture.Significantamountofworkon theiruseashealingstimulatorshasbeendone[51–57],alsoinvestigatingthemodificationstotheintrinsicconcrete micro-structurebroughtbythecrystallinereactionpromotedbytheadditives(Fig.8)[58].Moreover,aninterestingsynergywith thedispersedfibrereinforcementhasbeenobserved[54]:thefillingofthecracksbycrystallinehealingproductsislikelyto activateasortofchemicalpre-stressingthroughoutthecrackedmaterial,fromwhichthehealinginducedrecoveryofthe performanceislikelytobenefittoagreaterextentthaninthecaseofordinaryFRC[45](Fig.9).

Themultiplicityoftheperformance,sofaranalysedwithreferencetothematerial,canbeeasilyextendedtothescaleof thestructuralelement.

Fig.7. Microstrucreofhealedcrackinconcretewithout(a)andwith(b)crystallineadmixture[58].

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AnexampleistheconceptoflayeredcompositeelementproposedbydiPriscoetal.[59]whichemploysatopHPFRCClayeranda TextileReinforcedMortarbottomlayer,coupledbymeansofahighdensityPolystyrenepanel,whichperformsthestructuralfunction oftransmittingverylowshearstressesandisusedalsoforthermalinsulation(Fig.10).ThelowpermeabilityoftheHPFRCCinthe un-crackedstateanditsself-healingcapacityevenledtoavoidtheuseofawaterproofinglayer.Theseelementsarealso characterizedbyahighfireresistance:infact,whenafireoccurs,polystyrenesublimatesbecausethemeltingtemperatureof EPS(ExpandedPolystyrene)iscloseto160_C._If_suitable_escapes_for_the_smoke_are_introduced_and_a_fixing_device_is_designed_to

hangthetextilethinlayertotheupperHPFRCCplate,theempty chamberresultingthepolystyrenesublimationactsasanideal barrieragainstﬁreandtheTRCpanelworksasaﬁreshieldpreservingthestructuralbearingresistanceofthetopHPFRCCplate.

Fig.9.Pre-cracking/post-healingstressvs.crackopeningperformanceofHPFRCCspecimenswithout(a)andwith(b)crystallineadmixtures[54].

Fig.10.LayeredHPFRCC/TRCelementsontheprecastrunway(a)anddetail(b)[59].

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Fig.12.Retroﬁttingofshearwallcoupling-beamswithHPFRCC:testset-up(a);loadvs,driftperformanceforreferenceandretroﬁtted/upgradedmock-ups

(b);diagonalcrackinginanunreinforcedbeam(c)andintheunreinforcedsubgradeofaretroﬁttedone(d)ascomparedtomultiplecrackinginthe

retrofittedlayer(e);andnumerficalpush-overcurvesfordifferentretrofittingoptions,ascomparedtotheperformanceofuncoupledtwo-shaftwalland

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Theenhancedthermalperformancemakesthemextremelyattractiveforanenergyretroﬁttingofbuildings,notdisjoined fromalikewisehighefﬁciencyvs.earthquakeinducedactionsbecauseoftheirreducedself-weight[60,61].

4.5.Visibility

Itclearlyappears,fromwhatsyntheticallydescribedinthissection,thatUHPC/UHPFRCcanrepresentthestartingpoint forthedevelopmentofaconsistentmaterialandstructuraldesignapproachaimed,ontheonehand,atimprovingthe durabilityandreducingmaintenanceeffortsforstructuresexposedtoextremelyaggressiveexposures.Ontheother,through a “holistic”design approach, which tailors both the material composition and thecasting process totheanticipated structuralperformance,theorientationoffibrescouldbetailoredtomatchascloseaspossiblewiththedirectionofthe principaltensilestresswithinthestructuralelementwheninservice,sotoachieveamoreefficientstructuraluseofthe material.Thesuitablybalancedfresh-stateperformanceofHPFRCCswouldallowtomouldtheshapeofanelementand, thankstoatailoredcastingprocess,toorientthefibresalongthedirectionoftheprincipaltensilestressesresultingfromits structuralfunction.Inthiswayadesirableclosercorrespondencebetweentheshapeofanelementandthefunctionit performsinastructureassemblycouldbepursuedinthedesign.

Thisresultintoahigh_{“visibility”,}i.e.architecturalvalueofstructuresmadeofHPFRCC,which,startingfromthe_ﬁrst UHPCpedestrian bridgebuiltin Canadain 1997(Fig.11), are demonstratingontheﬁeld theirexcellentperformance throughouttheworld[23].

4.6.Consistency

Theaforementionedsuperiorperformanceinthefreshandhardenedstate,alsowithreferencetotheexpectedlongterm durability,makeHPFRCCsabletoprovideabreakthroughchangeinthecurrentdesignandconstructionpracticeforboth existingto-be-retroﬁtted[62–64]andnewstructures.

Withreference totheformer, theauthorreports itsown experiencewithreferencetothechallengingdesign and applicationscenariosuchastheupgrading/retrofittingofcouplingbeamsinearthquakeresistantshearwalls[65,66].An adequateselectionofthematerialallowedretrofittinglayersasthinas20mmtobeappliedonthesideandbottomfacesof thecouplingbeam,asfeasibleinthepracticeduetooperationalconstraints,andobtaintherequiredenhancementofthe loadbearinganddeformationcapacity(Fig.12a–b),accompaniedbyatransitionfromabrittlediagonalcracking(Fig.12c)to afailuremodecharacterizedbytheabilityofspreadingthelocalizeddamageintothesubgrade(Fig.12d)intomultipletiny cracks(Fig.12e).Thepossibilitywasalsoaddressedofextendingtheretrofittingdesignconceptfromthesingleelement isolatedfromitsstructuralcontexttoa_“model”shearwall,inordertogetback,evenifnotcompletely,thebehaviourone throughatailoredretrofitting,appliedonlytocouplingbeamsat“selected”storeys(Fig.12f).

Withreferencetonewconstructions,HPFRCCscanprovideabreakthroughchangeinthecurrentdesignandconstruction practice of infrastructures for energy harvesting from renewable sources, including wind, where also iconic feats characterizedbyahighengineeringandarchitecturalvaluearepossible.Focusingonon-shorewindturbinetowers,the projected and planned increase of wind-energyshare in thetotal power needof several countries, is leading tothe developmentanduseofhigherpowerturbines(e.g.from5to10MW)whichemployrotorswithdiametersequalto100mor larger.Atthisheight,severaloftheadvantagesofthecurrentsteeltowersarelostdue totheirlargersize,theirlower stiffness,andthenecessityforon-sitecompletion.Undertheseconditions,concretetowersbecomepracticablealternatives andeconomicallyattractive[67],providingtallerhubheightsandfeaturingadvantageswhich,besidesavarietyofboth precastandcast-in-placeconstructionoptionseasilyachievablethroughtheuseoflocallysourcedmaterialsandlabour,also includelowerprojectcostsandpotentialsforreductionoflogisticsandtransportationconstraints,improvedservicelifeand, quiteinterestingly,alsoforrepoweringwiththenextgenerationofturbines.

Lastbutnotleast,HPFRCCsareidealcandidatematerialstomeetthechallengesofimplementingadditivemanufacturing and3Dprintingtechnologiesintotheconstructionindustry.Asamatteroffact,thankstotheircompositionandbehaviour, theycanprovidea“structuralreinforcement”optionwhichwouldotherwisehavetobeincorporatedthroughalternative technologies [68], theirperformance alsobeneﬁts from a ﬁbre alignment almost inborn into, e.g., layered extrusion processing,atthesametimealsoallowingforshapeandstructuresizeoptimization[69].

5.Conclusions

In thispaper,moving fromaparallelwith“Sixmemos fromthenext millennium”byItaloCalvino,theauthorhas discussed,alsobasedonthemostsigniﬁcantresultsofitsresearchinthelasttenyears,hisownperspectiveonthecurrent stateontheuseofHPFRCCsincivilengineeringforbothnewandexistingbuildingsandstructures.

Thethread-linewhich,intheauthor’sopinion,hastoinformandgovernthebreakthroughpenetrationofHPFRCCsinto theconstruction market,movingfroma prescription-basedtoa performance-basedmaterial andstructural durability concept,aimsatthebreakthroughtargetoftheoverallresilience[70,71]oftheengineeringfeats,whichencompass: materialrobustness,i.e.lowsensitivitytochangesincomposition,handlingetc.,andstructuralrobustness,i.e.theability

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lossofperformance;thishastoinclude,ontheonehand,thedevelopmentofconstructiontechniquesreally“tailored”to theexploitthefullbeneﬁtsoftheadvancedperformanceofHPFRCCsand,ontheother,addressthepossibilityofrecycling thesamematerialsandassessthelevelofperformanceobtainablethroughsucha_{“rebirth”}approach;

structuralandmaterialredundancy,throughﬁt-for-the-purposestructureconceptandamaterialabletoprovide,also thankstoitsabilitytospreadthedamageintoasetofmultipletinycracks,multiple-scalebarrierstodegradation:material imperviousnessintheun-crackedstate,cracktightnessinthecrackedstateandactivationofself-healingfunctionalities uponcracking;

resourcefulnessandrapidity,throughsynergybetweenmaterialfunctionalitiesandtailoreddesign.

Thevisionhighlightedintheprevioussubsections,throughthevaluesoflightness,quickness,exactitude,multiplicityand visibility,shallbeconsistentlyscaledup,throughaholisticdesignapproach.Thishastomovefromthematerialtothe structuraldurabilitylevel,anticipatingtheevolutionofthestructureperformanceandquantifytheresultingincreaseinthe servicelifeofstructuresmadeofHPFRCC,andtherelatedoutcomesintermsofLifeCycleCostandSocialLifeCycleAnalysis, bothincradle-to-graveandcradle-to-gateapproach[72–74].

Moreover,itisworthalwayskeepinginmindthatnewmaterialstraditionallypushforthedevelopmentofnewstructural conceptsandnewconstructiontechnologies,andnotonlyforimprovementoftheexistingones.Inthisrespect,advanced manufacturingtechniques,suchasDigitalFabricationones,couldbereallyexploitedasakeyenablingtechnologytopushfor furtherspreadingofthecategoryofadvancedcementbasedmaterialshereindealtwith.

Acknowledgements

Inthispaper,which reﬂectsthepresentationgivenatBCCM-4inRiodeJaneiro,inJuly 2018,Ihavetried,inan intrepidparallel,tomergemypassionfortheItalianwriterItaloCalvinowiththeresultsofabout15yearsofresearchin theﬁeldofHighPerformanceFibreReinforcedCementitiousComposites.Iamindebtedtoprof.MarcodiPrisco,myPhD supervisor at Politecnico di Milano, and to prof. Surendra P. Shah, my supervisor during my Fulbright visiting scholarshipatNorthwesternUniversityin2006,who,throughtheirmentorship,haveinstilledmethewilltopursuea one-of-a-kind“holistic”perspectiverangingfrommaterialstostructuralapplicationswhichIhaveconstantlytriedto pursueinmywork.

References

[1]EuropeanCommission.TheEuropeanconstructionsector.Aglobalpartner.11/03/2016.16pp.

https://ec.europa.eu/growth/content/european-construction-sector-global-partner-0_en(Accessed1March2018).

[2]WEF, Shaping the Future of Construction. A Breakthrough in Mindset and Technology 61p, (2016) . http://www3.weforum.org/docs/

WEF_Shaping_the_Future_of_Construction_full_report__.pdf).

[3]The concrete conundrum, Chemistry World, March Accessed on March 1, 2018 through, (2008) , pp. 62–66. http://www.rsc.org/images/

Construction_tcm18-114530.pdf.

[4]H.S.Müller,M.Haist,M.Vogel,Assessmentofthesustainabilitypotentialofconcreteandconcretestructuresconsideringtheirenvironmentalimpact, performanceandlifetime,Constr.Build.Mater.67(2014)321–337.

[5]R.Gettu,R.G.Pillai,J.Meena,A.S.Basavaraj,M.Santhanam,B.S.Dhanya,etal.,Considerationsofsustainabilityinthemixtureproportioningofconcrete forstrengthanddurability,V.Falikman(Ed.),Durabilityandsustainabilityofconcretestructures(DSCS-2018),Proceedings2ndInternational Workshop(2018)ACISP326,5.1-5.16.

[6]B.L.Damineli,F.M.Kemeid,P.S.Aguiar,V.M.John,Measuringtheeco-efﬁciencyofcementuse,Cem.Concr.Compos.32(2010)555–562.

[7]PropertiesofFreshandHardenedConcreteContainingSupplementaryCementitiousMaterials.State-of-the-ArtReportoftheRILEMTechnical

Committee238-SCM,WorkingGroup4.In:N.DeBelieetal.,(eds.),Springer,2018,315+xxvpp.,ISBN978-3-319-70606-1.

[8]SupplementaryCementitiousMaterialsMarketbyType(FlyAsh,FerrousSlag,andSilicaFumes),GlobalOpportunityAnalysisandIndustryForecast,

2017-2023.(accessedonNov,14,2018throughhttps://www.alliedmarketresearch.com/supplementary-cementitious-materials-market).

[9]P.Chaunsali,P.Mondal,Inﬂuenceofcalciumsulfoaluminate(CSA)cementcontentonexpansionandhydrationbehaviorofvariousordinaryportland Cement-CSAblends,J.Am.Ceram.Soc.98(8)(2015)2617–2624.

[10]AlkaliActivatedMaterials:State-of-the-ArtReportoftheRILEMTechnicalCommittee224-AAM.In:Provis,J.andvanDeventer,J.,(eds.),Springer,

2014,388pp.,ISBN978-94-007-7672-2.

[11]CalcinedClaysforSustainableConcrete.Proceedingsofthe1stInternationalConferenceonCalcinedClaysforSustainableConcrete,In:ScrivenerK.

andFavier,A.,(eds.),Springer,2015,597+xvipp.,ISBN978-94-017-9939-3.

[12]CalcinedClaysforSustainableConcrete.Proceedingsofthe2ndInternationalConferenceonCalcinedClaysforSustainableConcrete.In:Martirena,F.

etal.,(eds.),Springer,2018,520+xxvipp.,ISBN978-94-024-1207-9.

[13]Recentadvancesongreenconcreteforstructuralpurposes.ThecontributionoftheEU-FP7projectEnCoRe.In:Barros,J.A.O.etal.,(eds.),Springer,2017,

pp.427+x,ISBN978-3-319-56797-6.

[14]J.Xiao,C.Qiang,A.Nanni,K.Zhanga,Useofsea-sandandseawaterinconcreteconstruction:currentstatusandfutureopportunities,Constr.Build. Mater.155(2017)1101–1111.

[15]S.Talukdar,N.Banthia,Carbonationinconcreteinfrastructureinthecontextofglobalclimatechange:modelreﬁnementandrepresentative concentrationpathwayscenarioevaluation,ASCEJ.Mater.CivilEng.28(4)(2016)04015178.

[16]https://inspectioneering.com/news/2016-03-08/5202/nace-study-estimates-global-cost-of-corrosion-at-25-trillion-ann(Accessed1March2018). [17]S.Matthews,CONREPNET:performance-basedapproachtotheremediationofreinforcedconcretestructures:achievingdurablerepairedconcrete

structures,J.Build.Apprais.3(1)(2007)6–20.

[18]EN1992-1-1,Eurocode2:DesignofConcreteStructures-Part1-1.December,(2004). [19]FibModelCodeforConcreteStructures,(2010),doi:http://dx.doi.org/10.1002/9783433604090.

[20]M.diPrisco,G.Plizzari,L.Vandewalle,Fiberreinforcedconcrete.Newdesignperspectives,Mater.Struct.42(9)(2009)1261–1281.

[21]A.E.Naaman,H.W.Reinhardt,ProposedclassiﬁcationofHPFRCcompositesbasedontheirtensileresponse,Mater.Struct.39(5)(2006)547–555. [22]H.Okamura,Selfcompactinghighperformanceconcrete,Concr.Int.19(7)(1997)50–54.

(15)

[23]UHPC,C.ShiB.ChenFuzhou,China,7-10November2018Proceedingsofthe2nd

InternationalConferenceonUHPCMaterialsandStructures2018,C.Shi, B.Chen(Eds.),Proceedingsofthe2nd

InternationalConferenceonUHPCMaterialsandStructures(2018)RILEMPubs.,832+xxiiipp.,ISBN: 978-2-35158-219-0.

[24]L.Ferrara,Y.D.Park,S.P.Shah,Amethodformix-designofﬁberreinforcedselfcompactingconcrete,Cem.Concr.Res.37(2007)957–971. [25]L.Ferrara,M.diPrisco,N.Ozyurt,SelfconsolidatinghighperformanceSFRC:anexampleofstructuralapplicationinItaly,in:C.M.Aldea,L.Ferrara

(Eds.),FiberReinforcedSelfConsolidatingConcrete:ResearchandApplication,2010,pp.109–128ACI-SP274,ISBN0-87031-398-3.

[26]L.Ferrara,A.Meda,Relationshipsbetweenﬁbredistribution,workabilityandthemechanicalpropertiesofSFRCappliedtoprecastroofelements, Mater.Struct.39(4)(2006)411–420.

[27]L.Ferrara,Y.D.Park,S.P.Shah,Correlationamongfreshstatebehaviour,ﬁberdispersionandtoughnesspropertiesofSFRCs,ASCEJ.Mater.CivilEng.20 (7)(2008)493–501.

[28]L.Ferrara,N.Ozyurt,M.diPrisco,Highmechanicalperformanceoffiberreinforcedcementitiouscomposites:theroleof“casting-flow”inducedfiber orientation,Mater.Struct.44(1)(2011)109–128.

[29]L.Ferrara,P.Bamonte,A.Caverzan,A.M.Musa,I.Sanal,AcomprehensivemethodologytotesttheperformanceofSteelFibreReinforced Self-CompactingConcrete(SFR-SCC),Constr.Build.Mater.37(2012)406–424.

[30]P.Stahli,J.G.M.vanMier,Manufacturing,ﬁbreanisotropyandfractureofhybridﬁbreconcrete,Eng.Fract.Mech.74(2007)223–242.

[31]P.Stahli,R.Custer,J.G.M.vanMier,Onflowproperties,fibredistribution,fibreorientationandflexuralbehaviourofFRC,Mater.Struct.41(1)(2008) 189–196.

[32]L.Ferrara,M.Faifer,S.Toscani,AmagneticmethodfornondestructivemonitoringofﬁberdispersionandorientationinSteelFiberreinforced CementitiousComposites–part1:methodcalibration,Mater.Struct.45(4)(2012)575–589.

[33]L.Ferrara,M.Faifer,M.Muhaxheri,S.Toscani,AmagneticmethodfornondestructivemonitoringofﬁberdispersionandorientationinSteelFiber ReinforcedCementitiousComposites–part2:correlationtotensilefracturetoughness,Mater.Struct.45(4)(2012)591–598.

[34]M.diPrisco,L.Ferrara,M.G.L.Lamperti,DoubleEdgeWedgesplitting(DEWS):anindirecttensiontesttoidentifypost-crackingbehaviourofﬁbre reinforcedcementitiouscomposites,Mater.Struct.46(11)(2013)1893–1918.

[35]L.Martinie,N.Roussel,Simpletoolsforﬁberorientationpredictioninindustrialpractice,Cem.Concr.Res.41(2011)993–1000.

[36]N.Roussel,A.Gram,M.Cremonesi,L.Ferrara,K.Krenzer,V.Mechtcherine,S.Shyshko,J.Skocek,J.Spangenberg,O.Svec,L.N.Thrane,K.Vasilic, Numericalsimulationsofconcreteﬂow:abenchmarkcomparison,Cem.Concr.Res.69(2016)265–271.

[37]M.Cremonesi,L.Ferrara,A.Frangi,U.Perego,SimulationoftheﬂowoffreshcementitioussuspensionsbyaLagrangianFiniteElementapproach,J. Non-Netwon.FluidMech.165(2010)1555–1563.

[38]L.Ferrara,M.Cremonesi,M.Faifer,S.Toscani,L.Sorelli,M.A.Baril,J.Réthoré,F.Baby,F.Toutlemonde,S.Bernardi,Structuralelementsmadewithhighly ﬂowableUHPFRC:correlatingComputationalFluidDynamics(CFD)predictionsandnon-destructivesurveyofﬁberdispersionwithfailuremodes,Eng. Struct.133(2017)151–171.

[39]L.Ferrara,N.Tregger,S.P.Shah,Flow-inducedﬁberorientationinSCSFRC:monitoringandprediction,in:K.H.Khayat,D.Feys(Eds.),Design,Production andPlacementofSelfConsolidatingConcrete,ProceedingsSCC2010,6thInternationalRILEMSymposiumand4thNorthAmericanConfereneconthe DesignandUseofSCC,SeptemberMontreal,Quebec,Canada,26-29,Springer,2010,pp.417–428.

[40]L.Ferrara,M.Cremonesi,Effectsofcastingprocessontoughnesspropertiesofﬁberreinforced-selfcompactingconcreteasfromEN14651,N.Roussel, H.Bessaies-Bey(Eds.),RheologyandProcessingofConstructionMaterials,Proceedings7thRILEMInternationalConferenceonSelfCompacting Concreteand1stRILEMInternationalConferenceonRheologyandProcessingofConstructionMaterials(2013).

[41]S.P.Shah,P.Hou,etal.,Nano-engineeredmetacement-basedmaterialsanddurability,V.Falikman(Ed.),DurabilityandSustainabilityofConcrete Structures(DSCS-2018),2018Proceedings2ndInternationalWorkshop(2018).

[42]S.P.Shah,M.Konsta-Gdoutos,UncouplingModulusofelasticityandstrength,Concr.Int.39(11)(2017)37–42.

[43]B.Han,L.Zhang,J.Ou,SmartandMultifunctionalConcreteTowardSustainableInfrastructures,Springer,2017400pp.ISBN978-981-10-4348-2. [44]N.Banthia,O.Onuaguluchi,D.Chi,etal.,Bio-inspired,internallycuredcelluloseﬁberreinforcedconcretefornextgenerationinfrastructure,V.Falikman

(Ed.),DurabilityandSustainabilityofConcreteStructures(DSCS-2018),2018Proceedings2ndInternationalWorkshop(2018)ACISP326,1.1-1.18. [45]E.A.Cuenca,L.Ferrara,Self-healingcapabilityofFiberreinforcedConcretes.Stateoftheartandperspectives,J.KoreanSoc.Civ.Eng.21(7)(2017)2777–

2789.

[46]N.DeBelie,E.Gruyaert,A.Al-Tabbaa,P.Antonaci,C.Baera,D.Bajare,A.Darquennes,R.Davies,L.Ferrara,T.Jefferson,C.Litina,B.Miljevic,A.Otlewska,J. Ranogajec,M.Roig-Flores,K.Pain,P.Lukowski,P.Serna,J.M.Tulliani,S.Vucetic,J.Wang,H.M.Jonkers,Areviewofself-healingconcretefordamage managementofstructures,Adv.Mater.Interfaces5(17)(2018)1–28.

[47]L.Ferrara,S.R.Ferreira,V.Krelani,M.DellaTorre,F.Silva,R.D.ToledoFilho,etal.,NaturalﬁbresaspromotersofautogenoushealinginHPFRCCs:results fromanon-goingItaly-Brasilcooperation,M.A.Chiorino(Ed.),DurabilityandSustainabilityofConcreteStructures(2015)1-3ACISP305,11.1-11.10. ISBN-13:978-1-942727-44-6.

[48]S.K.Gosh(Ed.),Self-HealingMaterials:Fundamentals,DesignStrategies,andApplications,Wiley,2009ISBN9783527318292.

[49]L.Ferrara,V.Krelani,F.Moretti,AutogenoushealingontherecoveryofmechanicalperformanceofHighPerformanceFibreReinforcedCementitious Composites(HPFRCCs):part2–correlationbetweenhealingofmechanicalperformanceandcracksealing,Cem.Concr.Compos.73(2016)299–315. [50]L.Ferrara,V.Krelani,F.Moretti,M.RoigFlores,P.SernaRos,EffectsofautogenoushealingontherecoveryofmechanicalperformanceofHigh

PerformanceFibreReinforcedCementitiousComposites(HPFRCCs):part1,Cem.Concr.Compos.83(2017)76–100.

[51]L.Ferrara,V.Krelani,M.Carsana,Afracturetestingbasedapproachtoassesscrackhealingofconcretewithandwithoutcrystallineadmixtures,Constr. Build.Mater.68(2014)515–531.

[52]M.Roig-Flores,S.Moscato,P.Serna,L.Ferrara,Self-healingcapabilityofconcretewithcrystallineadmixturesindifferentenvironments,Constr.Build. Mater.86(2015)1–11.

[53]M.RoigFlores,F.Pirritano,P.SernaRos,L.Ferrara,Effectofcrystallineadmixturesontheself-healingcapabilityofearly-ageconcretestudiedbymeans ofpermeabilityandcrackclosingtests,Constr.Build.Mater.114(2016)447–457.

[54]L.Ferrara,V.Krelani,F.Moretti,Ontheuseofcrystallineadmixturesincement-basedconstructionmaterials:fromporosityreducerstopromotersof selfhealing,SmartMater.Struct.25(2016)08400217pp.

[55]R.P.Borg,E.Cuenca,E.M.GastaldoBrac,L.Ferrara,Cracksealingcapacityinchloriderichenvironmentsofmortarscontainingdifferentcement substitutesandcrystallineadmixtures,J.Sustain.Cem.Mater.7(3)(2018)141–159.

[56]E.Cuenca,A.Tejedor,L.Ferrara,Amethodologytoassesscracksealingeffectivenessofcrystallineadmixturesunderrepeatedcracking-healingcycles, Constr.Build.Mater.179(2018)619–632.

[57]P.Escoffres,C.Desmettre,J.P.Charron,Effectofacrystallineadmixtureontheself-healingcapabilityofhigh-performanceﬁberreinforcedconcretesin serviceconditions,Constr.Build.Mater.173(2018)763–774.

[58]L.Ferrara,S.Kassavetis,F.LoMonte,M.Stefanidou,CharacterizationofSelf-HealingReactionProductsinCementitiousMortarsviaNano-Indentation: across-collaborationintheframeworkofCOSTActionSARCOS,submittedforpresentationatNICOM-6,SixthInternationalSymposiumon NanotechnologyinConstruction(2018).

[59]M.diPrisco,L.Ferrara,M.G.L.Lamperti,S.Lapolla,A.Magri,G.Zani,Sustainableroofelements:aproposalofferedbycementitiouscomposite technology,M.N.Fardis(Ed.),InnovativeMaterialsandTechniquesinConcreteConstruction,ProceedingsACESWorkshop(2012)167–182. [60]I.Colombo,M.Colombo,M.diPrisco,etal.,TRCprecastFaçadesandwichpanelforenergyretroﬁttingofexistingbuildings,M.A.Chiorino(Ed.),

DurabilityandSustainabilityofConcreteStructures(2015)ACISP305,30.1-30.10.ISBN-13:978-1-942727-44-6.

[61]M.C.Caruso,C.Menna,D.Asprone,A.Prota,G.Manfredi,Methodologyforlife-cyclesustainabilityassessmentofbuildingstructures,ACIStruct.J.114 (2)(2017)323–336.

(16)

[62]G.Martinola,A.Meda,G.A.Plizzari,Z.Rinaldi,StrengtheningandrepairofRCbeamswithﬁberreinforcedconcrete,Cem.Concr.Compos.32(2010) 731–739.

[63]A.Meda,S.Mostosi,P.Riva,ShearstrengtheneingofreinforcedconcretebeamwithHPFRCCjacketing,ACIStruct.J.111(5)(2014)1059–1068. [64]M.Preti,A.Meda,RCstructuralwallwithun-bondedtendonsstrengthenedwithHPFRC,Mater.Struct.48(1–2)(2015)249–260.

[65]B.A.Canbolat,G.J.Parra-Montesinos,J.K.Wight,Experimentalstudyonseismicbehaviorofhighperfor-manceﬁber-reinforcedcementcomposite couplingbeams,ACIStruct.J.102(1)(2005)159–166.

[66]M.Muhaxheri,A.Spini,L.Ferrara,M.diPrisco,M.G.L.Lamperti,etal.,Strengthening/retroﬁttingofcouplingbeamsusingadvancedcementbased materials,F.Dehn(Ed.),ProceedingsICCRRR2015,4thInternationalConferenceonConcreteRepair,RehabilitationandRetroﬁtting(2015)733–741. [67]ITG-9R-16:ReportonDesignofConcreteWindTurbineTowers,AmericanConcreteInstitute,2016.

[68]D.Asprone,C.Menna,F.P.Bos,T.A.M.Salet,J.Mata-Falcón,W.Kaufmann,Rethinkingreinforcementfordigitalfabricationwithconcrete,Cem.Concr. Res.112(2018)111–121.

[69]D.Asprone,F.Auricchio,C.Menna,V.Mercuri,3Dprintingofreinforcedconcreteelements:technologyanddesignapproach,Constr.Build.Mater.165 (2018)218–231.

[70]M.Bruneau,A.Reinhorn,Overviewoftheresilienceconcept,Proceedingsofthe8thU.S.NationalConferenceonEarthquakeEngineering,April18-22 (2006).

[71]P.M.Bocchini,D.M.Frangopol,T.Ummenhofer,T.Zinke,ResilienceandsustainabilityofcivilInfrastructure:towardauniﬁedapproach,J.Infrastruct. Syst.20(2)(2014)1–16.

[72]D.M.Frangopol,M.Liu,Maintenanceandmanagementofcivilinfrastructurebasedoncondition,safety,optimization,andlife-cyclecost,Struct. Infrastruct.Eng.3(1)(2007)29–41.

[73]M.M.Khasreen,P.F.G.Banﬁll,G.F.Menzies,Life-cycleassessmentandtheenvironmentalimpactofbuildings:areview,Sustainability1(3)(2009)674– 701.