Abstract: Sulfate corrosion process of the cast-in-situ piles in the saline area was simulated by laboratory experiments. Comparison study of degradation process and sulfate diffusion laws of cast-in-situ pile concrete was conducted to reveal the degradation mechanism. Cast-in-situ concrete specimens were manufactured and immersed in sulfate solutions to reproduce the completely and semi-immersed service conditions of cast-in-situ concrete piles in practical engineering. The size changes were recorded after 1, 3, 6 and 9 months. The compressive strength test was conducted and the sulfate concentration of different depths in concrete were measured to reveal the differences of degradation process in different service conditions. The effect of service condition on diffusion properties of sulfate in pile concrete were analyzed based on the experiments. Results show that degradation process of concrete and sulfate diffusion in concrete are quite different in different service conditions. The deterioration of concrete semi-immersed in sulfate solution is faster than those completely immersed below the liquid surface. Expansion and shedding of concrete are detected since sulfate chemical and crystallization conducted on the surface of semi-immersed specimens. The sulfate diffusion ratio in concrete above the liquid surface is more rapid than that of specimens completely immersed in sulfates solution. Results indicate that pile concrete above the groundwater level suffers greater damage and encounters more serious degradation in a relatively short time. The deterioration of pile concrete below groundwater level is relatively slow since the serving environment is stable and only chemical attack is encountered. The anti-sulfate attack of cast-in-situ pile concrete near the groundwater level should be considered in the design of pile foundation in sulfate saline area.

Key words: cast-in-situ pile concrete, sulfate attack, sulfate diffusion properties, corrosion forms, degradation process