Research On Fracture Energy Of Cementitious Materials In Sulfate Environment

Sulfate ions are rich in the water and soil of the coastal area in North China and the Saline Lake area of the western part of China. The seasonal temperature variation frequently occurs in these regions, which cause the erosion damage of the concrete. In the complicated and detrimental environment, the cement based material suffers the attacking from the sulfate ions and finally fails in carry loading. The initial damage of concrete is caused by the interior micro-crack development that is due to ettringite expansion. Hence, the fracture energy that is sensitive to the micro-crack developments, was employed to investigate the initial cracking in the cement based material caused by sulfate intrusion. In this way, the damage of cement based material due to the sulfate intrusion can be predicted at the early stage so that effective methods can be taken to slow down or prevent the cracking in the material.The properties of the mortar subject to sulfate environment have been investigated in the following respects:(1) The mortar samples produced by portland cement and high-sulfate-resistance cement with different water/cement ratio were immersed in the solution of sulfate sodium solution with concentration 5%. Subsequently, the appearance of the mortars was under routine observations. It is found that the surface of the mortar produced by Portland cement with water cement ratio 0.6 was destroyed significantly.(2) To the mortar samples soaked in solution at different ages, length variation test, compressive and bending test, and the relative dynamic elastic modulus test are taken as the basic for the fracture energy test. From these experiments, we study the basic mechanical properties of mortar samples immersing in the sulfate solution. From the studying, the water cement ratios and the types of binding materal have obvious effects on the performance.(3) The mortar samples soaked at different ages are operated by a three-point bending beam test, which gives the corresponding force-displacement relation. consftsoftwareisemployedtofitthebilinearmodelsandderivestrainsofteningrelation,andfinallygivethecorrespondingchangeinthevalueofthefractureenergy.relyingonthestudy,theultimatestress,toughnessandfractureenergyofsampleswithhighw/cratioincreasedfirstandthendecreased.alltheindexesofothergroupsareincreasedwiththeimmersingage.(4)foursurfacesofthemortarcubearesealedwithwax,leavingotheroppositeonesunsealed.theunsealedsurfacesareimmersedinthesolutionfordifferentagesandthesulfatecontentandpenetrationdepthhavebeentested.thesamplesaregrindedlayerbylayerbythegrindingmachine.thesulfatecontentinthegrindedpowderfromeachlayerwasmeasuredandthereactedsulfateamountcanalsobecalculated.itisobservedfromexperimentsthatlongerimmersedagesresultinthedeeperpenetrationdepthandmoresulfatecontentintrusion.also,thew/cratiohasgreatinfluenceonthetransportpropertiesforthesulfateionsincementbasedmaterials.(5)thesamplesfromeachgroupsofmortarsthatimmerse180daysinthesulfatesolutionsweremillinggrinding.throughtheusingofathermo-gravimetricanalyzer,theamountofformedettringitecanbecharacterized.thetgatestingcombinedwithresultsfromthesulfatetitrationtestconcludedthatthecontentofsulfatewasinfluencedbywatercementratioandcementbasematerial.