Leakageratethroughanon-crackedconcretewall,comparisonbetweentwosituations:AirpressuretestandaccidentconditionsOriginalResearchArticle

Abstract Thisexperimentalresearchinvestigatedthebehaviourofaconcretewall,withalocalzoneverypermeabletoair,subjectedtoaccidentconditions.Thehighlevelofpermeabilityintheconcretewasobtainedforonespecimenwithaporousconcretehavingconnectedpores(intrinsicpermeabilityof10−16m2). Theaimofthisworkwastostudycomparatively,inthelaboratory,thepermeabilityofanon-crackedconcretewallundertwoconditions.Acylindricalspecimen1.3mthickwasused.Noappreciablestresseswereappliedontheconcrete.Thefirstconditionwasatambienttemperature,underanincreasingpressure(upto0.42MPa)oftheairappliedononefaceofthespecimen,theotheronebeingatatmosphericpressure.Thesecondconditionwasanaccidentscenariowithsimultaneouseffectsoftemperatureandgas(amixofairandsteam)pressureappliedononeface,theotheroneremainingatatmosphericpressureandtemperature.Duringthetest,thelateralfaceofthecylindricalspecimenwasthermallyisolatedandmadeleaktight.So,auni-dimensionalexperimentalanalysiswasperformed.Theaccidentconditionsconsistedofarisefromambientconditionstoatemperatureof141°Candarelativepressureof0.42MPa(steampressureof0.377MPaandairpressureof0.043MPa)for3h,themaximumvaluesremainingconstantforseveraldays. Thermocouples,pressuretapsandmoisturegaugeswereimplantedinthespecimensatthemomentofcasting,toprovidelocalinformationabouttheinnerwallunderthesimultaneouseffectsoftemperatureandsteampressure.Outsidethespecimen,thechamberenclosedacondenserwithahumiditymeterandthermocouple,soitwaspossibletoquantifyseparatelythesaturatedairflowwithaflow-metreandthecondensedwater. Duringthepermeabilitytestatambienttemperature,thefieldofpressurewasaffectedbythevariationoflocalpermeabilityoftheconcrete.Furthermore,somemovementofinterstitialwaterinsidethespecimeninducedanincreaseofthepredictedoutflow,noliquidphaseappeared. Forthenaturalporousconcrete,duringaccidenttesting,thefieldofpressureadvancedslowly,theoutflowprogressivelyincreasedtoobtainamaximumat70h,afterthistimeontheonehandtheairflowratedecreasedandbecameequaltozero;ontheotherhand,theliquidflowratewasconstant,attheendofthetest,about30cmofthespecimenwaswatersaturated. Auni-dimensionalnumericalanalysiswasperformed.TheTHMmodel(non-saturatedporousmediathermo-hydro-mechanic)includedinCode_Aster®wasused.Twofluidphasescanbeconsideredinthematerial:aliquidphase(water)andagasphase(dryairplusvapour)withtheliquid/vapourphasechanges.Thethermodynamicaspectsdealtwithopensystemsframework,withtemperature,capillarypressureandgastotalpressureasvariables.Observingtheconsideredconditions(progressivesaturationofthewall),theshapeofsorptionisothermandpermeabilitieshadanimportantinfluenceontheresults.Thenumericalresultswereingoodagreementwithexperimentalresults,onthephenomenologyandonflowratethroughthewall. Thisstudygavesomeindicatorsabouttherelationsbetweenairflowduringapermeabilitytestandgas(air+steam)flowsduringaccidenttesting.