Quantification methods for chloride binding in Portland cement and limestone systems

Abstract

This paper presents a comparison of methods to quantify the chloride binding capacity for cementitious materials composed of Ordinary Portland Cement (OPC) and Limestone (LS, 0 to 55% replacement). Physical and chemical chloride bindings were investigated to better understand the binding capacity of the different systems and to provide basic information for modelling. Cement pastes samples were exposed to a 0.5 M NaCl solution and their chloride contents were quantified as free ions in pore solution, chemically bound ions in AFm phases, and physically bound ions on Calcium-Aluminum-Silicate-Hydrates (C–A–S–H). Notably, the study showed that (1) considering a solid solution between Friedel's salt and Hemicarboaluminate (Hc) was necessary for the quantification of chemically bound chlorides in limestone blended system and (2) an accurate estimation of the C–A–S–H content was critical for quantifying physically bound chlorides.