Durability Of Coal Gangue Concrete Under The Action Of Sulfate Attack And Freeze-Thaw And Dry-Wet Cycles

The north of China is rich in coal resources and has large reserves of coal gangue,which is convenient to use coal gangue locally and make up for the shortage of natural aggregate.Due to the influence of the environment,the concrete structure located in the northern area were greatly affected by the dry-wet cycle and freeze-thaw cycle,and also faced the influence of sulfate attack.If coal gangue was used as aggregate to prepare coal gangue concrete,it is necessary to study the deterioration damage of coal gangue concrete under the action of sulfate attack and freeze-thaw and dry-wet cycles.Therefore,experiments took coal gangue concrete specimens as the object to analyze the durability of coal gangue concrete under the action of sulfate attack and freeze-thaw and dry-wet cycles.The non-spontaneous combustion coal gangue in Tangshan mining area was used to partially replace natural gravel to prepare concrete specimens.The degradation law of freeze-thaw resistance,dry-wet resistance and freeze-thaw-dry-wet resistance of coal gangue concrete in two test media of water and 5%Na2SO4 solution were studied.The effects of coal gangue coarse aggregate replacement rate,sulfate solution concentration and cycle times on mass loss rate,relative dynamic elastic modulus,ultrasonic wave velocity rate and damage layer thickness of coal gangue concrete are discussed.The damage degree of coal gangue concrete is defined.Based on the measured values,Origin is used to fit the damage degree and the ultrasonic wave velocity rate,so as to predict the internal damage of coal gangue concrete under the action of sulfate attack and freeze-thaw and dry-wet cycles by ultrasonic nondestructive testing method.The sulfate attack and freeze-thaw and dry-wet damage model of coal gangue concrete was established,and the damage degree of coal gangue concrete was predicted by using the parameter f of coal gangue coarse aggregate replacement rate and the number n of sulfate attack and freeze-thaw and dry-wet cycles.The results show that:(1)the freeze-thaw resistance of concrete decreases with the increase of the replacement rate of coal gangue coarse aggregate,while the dry-wet resistance of concrete increases slightly with the increase of the replacement rate of coal gangue coarse aggregate.Sulfate attack reduces the freeze-thaw resistance and dry-wet resistance of coal gangue concrete.The influence of dry-wet cycles on the quality damage and compactness of concrete is much less than that of freeze-thaw cycles.(2)The freeze-thaw and dry-wet resistance of concrete decreases with the increase of the replacement rate of coal gangue coarse aggregate.5%Na2SO4 solution will weaken the damage of coal gangue concrete at the early stage of cycle,and will aggravate the damage of coal gangue concrete at the late stage of cycle.The coupling effect of freeze-thaw and dry-wet will aggravate the durability damage of coal gangue concrete.(3)Compared with the sulfate attack and freeze-thaw action,the combined action of sulfate attack and freeze-thaw and dry-wet weakened the damage degree of coal gangue concrete in the early stage and increased in the later stage.The damage degree of coal gangue concrete under sulfate attack and freeze-thaw and dry-wet cycles is always greater than that under sulfate attack and dry-wet cycles.(4)Under the action of sulfate attack and freeze-thaw and dry-wet cycles,the relation between ultrasonic wave velocity rate and and the number of cycles of coal gangue concrete is cubic polynomial,the relationship between the thickness of damaged layer and the replacement rate of coarse aggregate of coal gangue concrete is quadratic polynomial,the relationship between the ultrasonic wave velocity rate and the damage degree of coal gangue concrete is cubic polynomial,and the fitting effect are good.(5)A sulfate attack and freeze-thaw and dry-wet damage model of coal gangue concrete was established considering the replacement rate and the sulfate attack and freeze-thaw and dry-wet cycle times.