Study On The Durability Of Concrete Subjected To Chloride Salt And Freeze Thaw

Salt damage and freeze damage are the two main disasters of the durability of concrete structures.The durability of concrete structures deteriorates gradually,and the service life of concrete structures reduces due to the coupling effects of chloride salt and freeze thaw in the north of China.Recently,the fly ash has been widely applied in concrete as a kind of mineral admixture.The later strength of fly ash concrete is higher than that of ordinary concrete,and the resistance to chlorides of fly ash concrete is stronger compared to that of ordinary concrete.But the salt freezing property of fly ash concrete is still indeterminate.As a result,the resistance to salt freezing of fly ash concrete was experimentally investigated in this paper.This may provide a good reference for the use of fly ash concrete,and therefore has a certain application value and economic benefit.Based on the technology project of Shandong Provincial Department of Housing and Urban Rural Development?No.KY009?,the outer appearance,compression strength,ratio of mass loss,dynamic elastic modulus and chloride concentration distribution of concrete with different fly ash after a number of cycles of salt freeze as well as the compression strength prior to any salt freeze cycles were studied.Further,the deterioration mechanism of fly ash concrete for salt freeze was explained microscopically by using methods of scanning electron microscopy?SEM?and energy dispersive spectrometer?EDS?.The test results indicate that the later compression strength of 180 days of the fly ash concrete is generally higher than those of ordinary concrete without fly ash when the content of fly ash in concrete is no more than 30%;the salt freeze cycles have significant effects on the durability properties of fly ash concrete,and the severity from big to small is as follows: the cube compression strength,cube weight loss rate,prism dynamic elastic modulus,prism weight loss rate rate;the amount of erosion of concrete surface mortar is much higher than that of ordinary concrete when the content of fly ash in concrete is greater than or equal to 15%;the cubic compression strength is reduced sharply,the ratio of mass loss is enlarged gradually,and the dynamic elastic modulus of fly ash concrete is also reduced after they subject to salt freeze cycles;the invasion of chloride ion is postponed due to the secondary hydration reaction of fly ash,but the damage of freeze-thaw cycle is very serious leading to the offset of the positive effect of fly ash on the resistance to chlorides;the freeze-thaw damage is aggravated due to the coalescence of pores and cracks of fly ash concrete after they bear a certain number of cycles;the content of ettringite in concrete is increased for the addition of fly ash,and a lot of Ca?OH?₂ crystals are consumed due to the secondary hydration of fly ash and invasion of chloride ions leading to a decrease of the p H value of concrete,and also the solidification of chloride ion is not directly influenced by the hydration of fly ash.