Effect of calcium leaching on the characteristics of chloride physical adsorption and chemical binding of cement-based materials

Abstract

Chloride corrosion is an important reason for the degradation of bearing capacity of reinforced concrete structures. When chloride ions transport from external environment into concrete, a part of ions will be bound by the cement matrix through the behaviors of chemical binding and physical adsorption. In this paper, the cement paste samples (R0, R5 and R15) with different degrees of calcium leaching are prepared to investigate the chloride binding capacity, by performing the experiment of chloride isothermal adsorption and desorption. In the experiment, the R0, R5 and R15 are immersed into NaCl-CH composite solutions with different chloride concentrations (Cf-Cl). The change of total binding chloride ion (TBCI), physically adsorbed chloride ion (PACI) and chemically bound chloride ion (CBCI) concentrations in the samples with Cf-Cl is obtained. Then, the linear and nonlinear adsorption laws are adopt to fit the experimental data of chloride concentrations, and the most appropriate adsorption laws are determined separately for the behaviors of TBCI, PACI and CBCI. Finally, the equations for chloride binding capacity of R0, R5 and R15 are obtained, which can be used to analyze the capacity of TBCI, PACI and CBCI of cement-based materials subjected to calcium leaching.