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                    Microstructureevolutionofhydrationproductsoftricalcium silicateunderdissolution

                                      LIWenwei,LIShuguang,LIXinyu,YANGHuamei
                                (ChinaThreeGorgesCorporation,HydraulicConcreteInstitute,Beijing 100038,China)

                  Abstract:Thedamconcreteintheunderwaterzoneissusceptibletodissolutiondamageduetotheleachingofcal
                  ciumions,whichresultsinthedecalcificationanddissolutionofcementhydrationproducts,andfurtherleadsto
                  thedeteriorationandfailureofthedamconcreteperformance.Todeeplyrevealthedeteriorationmechanismofdam
                  concrete ,itisnecessarytoclarifytheevolutionlawofthemorphologyandmicrostructureofcementhydrationprod
                  uctsunderdissolution.Asthemainmineralphaseofcement ,thehydrationproductcharacteristicsoftricalciumsil
                  icate(C 3 S)significantlyaffecttheperformanceofcementandconcrete.Therefore,high - purityC 3 Swasprepared
                  andthen soaked in ammonium chloride solution with differentconcentrationsafterhydration , to simulate
                  accelerateddissolutionprocedureofcementhydrationproducts.Thecomposition ,micro - nanostructureandmor
                  phologyofthedissolvedproductswereinvestigatedbycombiningthermogravimetricanalysis,nuclearmagneticres
                  onance ,scanningelectronmicroscopeandnitrogenadsorption.TheresultsshowedthatthehydrationproductofC 3 S
                  wasneutralizedwiththeammonium chloridesolution ,andthepH valueofthesolutionincreased.ThelowerpH
                  valueandmoreobviouslydecalcifiedofthehydrationproductsafterreactionwiththeincreaseoftheconcentrationof
                  ammoniumchloride ,demonstratedthatthedissolutiondegreeiscloselyrelatedtoenvironmentalconditions.The
                  dissolutionwouldreducethechemicalbindingwatercontentofthehydratedcalciumsilicate (C - S - H)gelamongce
                  menthydrationproducts ,causethepolymerizationofthesiliconchainstructure,coarsentheporestructureandin
                  tensifythehollownessofC - S - Hgel.Thedeteriorationdegreeofstructureandmorphologyincreasedcontinuously
                  withtheincrementofdissolutiondegree ,whichprovidestheoreticalbasisforexplanationofconcretedissolution
                  mechanismatmicro - nanoscale.
                  Keywords:dissolution;C 3 S;C - S - Hgel;chemicalboundwater;siliconnuclearmagnetic;micromorphology


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