Influence of clay pozzolanicity on compressive strength and capillary water absorption in LC3 cement matrices

This study investigated the influence of the pozzolanicity of kaolinitic clays on the compressive strength and capillary water absorption of LC3 cement mortars. Two different clays (A and B) were calcined for 15 minutes at five temperatures (550, 650, 750, 850, and 950°C). The degree of dehydroxylation was evaluated by thermogravimetry, and the pozzolanic activity by the modified Chapelle test. Thus, 750°C was defined as the most appropriate condition to maximize clay reactivity while balancing energy efficiency and performance. Mortars were molded with two water/cement ratios (0.48 and 0.56) and analyzed in the fresh and hardened state at 7, 14, 28, and 63 days. The results demonstrated that clay B presented greater pozzolanic potential, with reactivity 134% higher than clay A, reflecting its favorable chemical composition. Therefore, LC3B mortars presented mechanical performance equivalent to or superior to the reference samples, in addition to lower capillary absorption, surpassing REF samples by up to 36% and LC3A by 60%. In contrast, LC3A mixes presented inferior results, attributed to the lower reactivity of clay A. It was concluded that proper clay selection and control of calcination conditions are crucial for the development of pozzolanicity and the performance of LC3 cements. Consequently, LC3 has potential as a sustainable alternative to Portland cement, presenting a significant reduction in CO2 emissions without compromising mechanical properties.