ABSTRACT
Limestone powder has been used to replace part of Portland cement because of environmental and economic benefits. The durability of the cement-based materials is important to consider the performance of concrete structures under a long-term service life. Under a marine environmental condition, the chloride-induced corrosion is the main mechanism for the degradation of reinforced concrete structures. In this study, the effects of limestone addition on the pore structure, chloride binding capacity and apparent chloride diffusivity of Portland cement paste were investigated. The porosity and pore size distribution were obtained by mercury intrusion porosimetry, focused ion beam/scanning electron microscopy and X-ray computed tomography. The chloride binding isotherms and the binding kinetics of cement paste with different limestone addition were studied. The apparent chloride diffusivity was obtained by a ponding test. The MIP results showed that the addition of limestone powder led to a coarser pore structure, especially when more limestone powder was added or coarser limestone powder was used. Limestone powder accelerated the rate of chloride ion binding at first and then the binding rate slowed down as the absorption time increased. The bound chloride amount was larger as the particle size of limestone powder was smaller. The result also showed that cement paste containing 5% replacement of limestone powder had positive effect in resisting chloride ion penetration before 14 d of diffusion. For a longer diffusion time, the apparent chloride diffusivity of cement paste was greater with greater limestone powder content or larger limestone powder size.
