Abstract: Using manufactured sand, extra fine sand and other materials to prepare chloride resistance concrete is of great significance to reduce production costs and improve the service life of bridges in coastal areas. In this study, the chloride resistance of concrete was improved by optimizing aggregate design and cement paste composition. The effects of aggregate gradation, extra fine sand content, sand ratio, water-binder ratio and cementitious material type on concrete performance were studied. The results show that the chloride diffusion coefficient decreases from 4.0×10^-12 m²/s to 2.9×10^-12 m²/s when the mass fraction of 8~16 mm gravel increases from 50% to 80%. When 50% (mass fraction) manufactured sand is replaced by extra fine sand, the chloride diffusion coefficient is 3.6×10^-12 m²/s, which can still meet the design requirements. With the increase of sand ratio, the chloride diffusion coefficient decreases first and then increases. The water-binder ratio is controlled in the range of 0.36~0.38, and the chloride diffusion coefficient is less than 3.5×10^-12 m²/s. The hydration of slag component improves the pore structure of concrete, and forms more AFm and C-S-H, which improves the chloride binding capacity. The chloride diffusion coefficient of concrete with slag cement is 40% lower than that of OPC.

Key words: manufactured sand, extra fine sand, slag cement, chloride resistance, chloride diffusion coefficient, mechanical property