Effect of carbonation on chloride binding capacity of limestone calcined clay cement (LC3) and binary pastes

Abstract

Carbonation of hydrated cement paste not only directly impairs the durability of reinforced concrete structures, but also alters the chloride binding capacity of cement-based materials. Besides, incorporating supplementary cementitious materials (SCMs) may influence both the durability against carbonation and the chloride binding capacity of binders. In this study, the chloride binding capacities of Limestone Calcined Clay Cement (LC3) pastes, prepared with four different kaolinite clays from local resources, have been investigated. In addition, binary pastes containing calcined clays (CC), silica fume and limestone powder (LS) as SCMs were designated to compare their pore structures, compressive strengths and durability properties with LC3 blends. The durability against carbonation was investigated via carbonation depth measurement, determination of hydroxide ions reduction and qualitative evaluation of phase assemblage changes through XRD analysis. Additionally, the chloride binding capacity of pastes was measured by the equilibrium method and the effect of carbonation on chloride binding capacity has been studied. The thermogravimetric analysis was also conducted to quantify the portlandite and Friedel's salt content of paste specimens. Based on the results, LC3 mixtures had lower bound chloride and Friedel's salt contents than binary blends prepared with CCs, while the chloride binding capacity of carbonated binary and ternary CC incorporated pastes were nearly similar. Besides, although LC3 pastes had higher chloride binding capacity than binary SF and LS containing blends, they were more susceptible to carbonation. Moreover, the CO3-AFm phases had generally lower capability to bind chloride ions than hydration products of LS-free binders.