Chloride binding behavior of calcium silicate hydrates and Friedel's salt of pastes

Abstract

Understanding the chloride binding capacity of cement pastes is crucial to investigating the concrete durability. To characterize the chloride binding behavior of calcium silicate hydrates (C–S–H) and Friedel's salt (Fs), this study investigates the chloride binding capacity of four types of cement paste using chloride binding isotherms, analyzes the correlation between phase composition and chloride binding capacity, and discusses the evolution law of the chloride binding capacity of Fs and C–S–H. The results indicate that the influence of mineral admixtures on the chloride binding capacity of C–S–H is basically the same as that of pastes. Slag (SL) has a significant positive effect, while silica fume (SF) generally plays a negative role, and the effect of fly ash (FA) depends on the concentration of NaCl solution. As to the influence of chloride concentration, the chloride combined by per unit mass of C–S–H and Fs presents different evolution trends, and a concentration break-even point exists between C–S–H and Fs combined chloride. Notably, this point provides the insight into which substance occupies the majority of the total bounded chloride. Moreover, the impact of chloride concentration on the chloride binding capacity of pastes cannot be solely determined by the content of C–S–H and Fs, and the chloride combined by per unit mass of C–S–H and Fs at different chloride concentrations offers more relevance.