Effects of curing regimes on the chloride binding capacity of cementitious materials

Chloride ions play obvious adverse roles in the corrosion of reinforcing steel of concrete structure, which affects the durability and service life of reinforced concrete structure. The durability of hydrothermal cured precast concrete elements is usually lower than that of cast-in-situ concrete structures with the same strength grade, and therefore the chloride ion corrosion of precast concrete should be paid more attention. The chloride binding capacity of cement-based material with different curing regimes was investigated by SEM, XRD, solution titration, and Low-Field NMR. Results show that the curing regime has a significant effect on the microscopic morphology and structure of the hydration products, and consequently affect their ability to bind chloride ions. Under steam curing, the HO-AFm’s transformation had an effect on its chemical binding capacity, while the transformation of C-S-H gels into cellular network structure enhanced the physical adsorption capacity. Autoclave curing leads to the reduction of AFm and the conversion of C-S-H to tobermorite, which reduces the binding capacity of the sample to chloride ions. Furthermore, the addition of mineral admixtures containing more reactive Al-phase components is helpful to improve the ability of cementitious materials to bind chloride ions. For FA and GGBFS, the Al-phase in GGBFS is more soluble to react with chloride ions, and its binding effect is better than that of FA.