Effect of Sulfate on the Chloride Diffusion Behavior of Coral Aggregate Concrete in the Marine Tide Zone

Abstract

This paper studied the effect of sulfate on chloride diffusion behavior in coral aggregate concrete (CAC) in marine tide zone. Three water/binder ratios of CAC were designed for experimental analysis, and the mechanism of the effect of sulfate on chloride transport was investigated by different microscopic experimental methods. The test results show that the chloride content decreases with the decrease of water/binder ratio of CAC. At an equal number of drying-wetting cycles, the chloride content under the combined action of chloride and sulphate is lower than that under the sole action of chloride. The change of peak chloride content with time showed a linear function with the square root of erosion time, while the chloride diffusion coefficient gradually decreased with erosion time. Adding silica fume to CAC effectively reduced the chloride diffusion coefficient, with a decrease of 26.1 % ~ 46.2 %. The attenuation coefficient of CAC under chloride erosion was 16.4 % ~ 38.1 % higher than that under the combined action of chloride and sulfate. The chloride diffusion model was established, and the error between the calculated value of the model and the experimental value was within 16 %. Microscopic observations revealed that in the early stage of erosion, the sulfate erosion products ettringite and gypsum had a compacting effect on the CAC, but in the late stage of erosion, they produced expansion cracks, which accelerated the deterioration of CAC.