Study On Long-term Performance Of Fly Ash Concrete Under Coupled Axial Compression Loading And Sulfate Attack

The civil engineering industry is developing rapidly,but the service environment of concrete structures is getting worse.It is often subjected to the load of the environment and its own weight,and the double or even multiple factors are coupled to the damage of the structure.Environmental factors are most severely eroded by sulfate ions.Therefore,the coupling test of concrete load and sulfate attack is carried out to study the effects of fly ash factors,immersion methods,concentration of etching solution and stress level on concrete durability.The combination of experiment and theory is a deep analysis of the deterioration law of concrete.(1)The durability of ordinary concrete and fly ash concrete under sulfate attack was studied.The results show that the dry and wet cycle of sulphate significantly accelerates the damage degradation effect of ordinary concrete,but has little effect on fly ash concrete.The high concentration of erosion solution accelerates the damage process of concrete,and the change of concentration of erosion solution of fly ash concrete is more sensitive than ordinary concrete.Through the establishment of concrete durability damage model,it is found that the concrete damage rate increases with the increase of erosion age.The damage rate of ordinary concrete is higher than that of fly ash concrete.The damage rate of sulfate dry-wet cycle is greater than that of long-term immersion.By establishing the relationship between the concrete strength loss rate and the thickness of the corrosion layer,it is found that the influence of the concentration of the sulphate solution and the immersion method can be neglected when studying the relationship between the sulphate solution erosion,and the ordinary concrete is proposed based on the experimental data.General equation for ultrasonic flaw detection of fly ash concrete.(2)The durability of fly ash concrete under load and sulfate coupling was studied.The results show that under the action of load and sulfate attack,the strength deterioration law of fly ash concrete is basically the same as that of ordinary concrete.Under the coupling of 0%,30% and 45% stress level load,the quality and relative dynamic elastic modulus of concrete specimens Both the peak stress and the peak stress decrease first and then decrease with the age of erosion,while both of them decrease with the 60% stress level.Through the combination of mass loss rate and relative dynamic elastic modulus,the conclusions of the complementary and common analysis of the deterioration law of concrete under load and environment coupling are more convincing.By analyzing the concrete durability damage model considering the load level,it is found that the concrete damage rate and the damage rate increment increase with the increase of the concentration of the erosion solution,but the damage rate increment decreases with the increase of the stress level;In the initial stage of sulfate-eroded concrete,the negative erosion effect of the sulfate on the deterioration of coagulation is less than the filling compaction effect(related to the erosion effect of the test factors on the concrete),which shows that the concrete damage rate in the erosion solution is lower than that of the clean water control group,but The duration of negative erosion effect decreases with increasing concentration of erosion solution and axial stress load stress.(3)The constitutive relation between fly ash concrete and ordinary concrete under the coupling of load and sulfate erosion is compared and analyzed.Considering the influence of load stress ratio and erosion age,the calculation methods of control parameters α and β in different concentrations of erosion solution are obtained,and the fitting of the uniaxial compressive stress-strain curve of concrete under the coupling of axial compression and sulfate erosion is established.The equations,and compared with ordinary concrete,analyzed the difference of constitutive relations between the two concretes in the process of sulfate attack.The increments of α and β of fly ash concrete are smaller than ordinary concrete.By defining the reference erosion age,the calculation method of the axial load stress ratio threshold is proposed.The stress ratio threshold of fly ash concrete and ordinary concrete is about 35%,but the incorporation of fly ash greatly prolongs the sulfate attack concrete.At the baseline erosion age,the baseline erosion age was 34% longer than normal concrete when the sulfate solution concentration was 10%.