The Macro-and Meso-damage Mechanism Of Concrete Under Different Kinds Of Salt Attack

Corrosion of concrete is a kind of durable failure mode of concrete structure.Under the action of different types of salt corrosion,concrete structures often lose efficacy and become destroyed before their the design service life,and their performance for service period are also greatly reduced,which will severely restrict the cement-based composite materials for the practical engineering application in corrosive environment.In Northeast China,northwest area of saline land in Saline Lake area and the southeast coastal areas,it can be usually seen that buildings are buried under the saline soil,bridges are eroaded in the water and the coastal engineering are suffered from the sea.The main harmful ions are sulfate ion,chlorine ion and carbonate ion.Mechanism and effect of microscopic damage for concrete,deterioration of structural performance and durability destruction caused by different types of salt corrosion are totally different.Therefore,it is a important scientific problem to be solved that study of mechanism of concrete macro microscopic damage caused by different types of salt corrosion.In the actual engineering structure,the existence of morphology in the concrete pores leads different kinds of ions into concrete so that the performance of concrete is suffered huge impact.Macro physical and mechanical properties of concrete are determined by the changes of the concrete microscopic structure in erosion environments.With the migration,precipitation,crystallization,and expansion of salt and water,the damage of concrete microscopic structure leads to the macro durability destruction.Therefore,it is necessary to link macroscopic physical phenomena to microscopic structure damage.This paper is funded by the key project of National Natural Science Fund(41430642),the National Natural Science Foundation of China Youth Fund Project(51108207),the project Chinese Postdoctoral Science Foundation(2015M581403)and the National Key Laboratory of Frozen Soil Engineering Open Fund(SKLFSE201514)funding for the study of erosion of sulfate,according to the soil environment in Northeast saline soil area unique,for the first time as bicarbonate corrosive ion concrete,the concrete macro bicarbonate is corroded by the meso damage mechanism research The wetting drying cycle test,long-term immersion test and SEM test of concrete subjected to SO42-and HCO3-erosion are carried out,and in the test the mechanism of macroscopic and microcosmic damage by different salt corrosion is further analyzed through the combination of macroscopic level tests and microcosmic level research.The influencing factors include the corrosive anionic category,the concentration of erosion solution,the water cement ratio and the erosion time of concrete and gas content,and the relative dynamic modulus of elasticity and the quality loss of concrete in the test.Through the test and analysis,it is found that the concrete structure is at the interface of corrosive soil and air,or between corrosive ground water and surface water and air,and the erosion is most serious.The durability damage for concrete is the most serious by complex salts(carbonate and sulfate),the durability damage for concrete is less serious by sulfate,and damage by bicarbonate is the weakest.The relationship between the relative dynamic modulus of elasticity and the erosion time of concrete in wet and dry cyclic environment is obtained,which can predict the life of concrete materials in salt corrosion environment.Through a large number of SEM tests on single salt erosion and the state of the concrete erosion compound on the meso structure damage was studied,and the mechanical properties will be affected by the salt corrosion of concrete meso structure and analysis,reveals the essence of concrete structure under salt erosion.