Distance-associated chloride binding capacity of cement paste subjected to natural diffusion

Chloride binding capacity is usually quantified by chloride binding isotherms (CBIs). However, an important factor influencing chloride binding capacity, namely the internal chemical environment (ICE), cannot be represented in the conventional CBIs. Knowing the drawbacks of the conventional CBIs, this paper straightly put the emphasis on the distance-associated chloride binding capacity. Specimens undergoing natural diffusion were used for measuring the chloride binding capacity at different distance. CBIs, chloride binding profiles (CBPs), chemical profiles and microscopy result were performed to analyze the rules and mechanisms. From the results of CBIs and CBPs, it is found that the conventional laboratory-determined CBIs would overestimate the chloride binding capacity beyond a certain distance from the surface, and underestimate the chloride binding capacity near the surface. Based on the chemical profiles and the microscopy results, it is found that ICE changes greatly along with natural diffusion, and meanwhile the chloride binding capacity at different distance develops discriminatively with the ICE change. Plus, a hydroxyl-dependent chloride binding model is established to quantify the distance-associated chloride binding capacity. The model explains the difference between the conventional laboratory-determined CBIs and the natural-diffusion-determined CBIs, and it fits well with the test results. (C) 2016 Published by Elsevier Ltd.