Investigating the potential of low-grade calcined clays to produce durable LC3 binders against chloride ions attack

Abstract

Utilization of limestone calcined clay cements (LC3) as a recently developed ternary blends could be a promising economic approach to reduce the environmental impacts of Portland cement production. This study presents a comparative experimental investigation between LC3 mortars and binary blends, prepared with kaolinitic calcined clays as prominent sustainable resources of supplementary cementitious materials (SCMs). In this regard, four different low to high-grade kaolinitic clays, provided from various resources, were calcined and incorporated in both binary and LC3 blends. Furthermore, the pure Portland cement and limestone Portland cement blends were also prepared to compare the results with calcined clay containing mixtures. Thermogravimetric analysis (TGA) was performed on paste samples to study the phase assemblage of systems. Besides, compressive strength, water absorption and sorptivity, total and free chloride ions penetration profiles, and chloride ions diffusion coefficients of mortar mixtures have been investigated. According to experimental results, the pozzolanic reactivity of calcined clays is not only influenced by the metakaolin content and thermal activation process, but also by the crystallinity of these materials. Besides, although the compressive strength of binary and LC3 mortars may be lower than the control mixture, but the permeability and resistance against chloride ions ingress have been significantly enhanced. Ultimately, low-grade calcined clays have been recognized as a promising resource to produce LC3 blends with adequate durability against chloride ions ingress.