Performance of Impure Calcined Clay in Binary and Ternary Concrete Mixtures Containing Portland and Slag Cements

Portland cement (PC) substitution with supplementary cementitious materials (SCM) is one of several strategies aimed at achieving the concrete industry's goal of cutting its CO2 emissions. While a high replacement level of PC (50%+) is achievable using slag cement (S), it may result in performance challenges such as delayed setting, increased shrinkage, and susceptibility to deicing salt scaling. Meanwhile, calcined clay (CC) has gained traction as an abundant and promising new SCM source to address the shortage of conventional SCMs such as coal fly ash and slag. This study evaluates the performance of low-purity CC in binary and ternary (in combination with slag) mixtures to replace PC by up to 50% and tests their fresh and hardened properties and durability. It is observed that the ternary mixture provides identical strength compared to control and binary CC (CC20) mixtures while possessing better ASR mitigation and chloride ion resistance.