Experimental Research Of Sulfate Corrosion Resistance Of Fresh Concrete

The durable performance of fresh concrete under sulfate corrosion environment was studied. Two kinds of corrosive medium, Na2SO4and MgSO4, were considered. The solution concentration of Na2SO4is5000mg/L and50000mg/L, and the solution concentration of MgSO4is4225mg/L and42250mg/L. Specimens were completely immersed in sulfate solution which was aimed at simulating the real corrosion environment. The compressive strength, rebound value and mass of concrete specimens in different corrosion ages (30d,90d,180d,270d and360d) were measured corresponding to different mixing percentage (0%,15%,20%,25%,30%and35%) of fly ash. The evaluation index is corrosion resistance coefficient of compressive strength, rebound value and mass-change rate. Some of concrete specimens were analyzed by using SEM and XRD technology. The sulfate corrosion resistance of fresh concrete was analyzed at both macro level and micro level.The results indicate that the sulfate corrosion resistance of fresh concrete is better than that of precast concrete within the experimental period of360days. The sulfate corrosion resistance can be improved by mixing with a certain amount of fly ash both for fresh concrete and precast concrete. The experimental research indicates that the optimal mixing amount of fly ash is25%for specimens immersed in magnesium sulfate or sodium sulfate solution. A regression equation was proposed to predict the compressive strength of fresh concrete and precast concrete corroded by sulfate on the base of rebound values of specimens. The development tendency of calculated compressive strengths agree well with experimental values.For fresh concrete and precast concrete both fully immersed in corrosive solution, the higher the corrosion medium concentration, the more serious the corrosion extent of concrete will be. The influence on the sulfate corrosion resistance of concrete by different corrosion medium is various, which is related to the concentration of corrosive medium. In sodium sulfate solution, the corrosion extent of concrete in the extreme corrosion environment is more serious than that in the general corrosion environment. In magnesium sulfate solution, the sulfate corrosion resistance of concrete in the extreme and general corrosion environment is both related to the amount of fly ash. A calculation model of the compressive strength for corroded concrete is created and a modified formula of corrosion resistant coefficient of compressive strength in degradation stages is proposed. The theoretical calculation results are in good agreement with the experimental values which indicates that the proposed modified formula can predict the degradation law of corrosion resistant coefficient of compressive strength of corroded concrete in degradation stages.