Influence of activation temperature on reaction kinetics in recycled clay waste-calcium hydroxide systems

Obtaining pozzolanic materials from recycling of industrial waste and byproducts is a priority action of environmental policy all over the world. This paper describes the effect of activation conditions on the reaction kinetics in calcined clay waste (CCW)/calcium hydroxide systems. The CCW used in this work shows excellent qualities for use as supplementary cementing material in the manufacture of commercial blended cements. This research work presents an exhaustive study about the kinetics of a pozzolanic reaction in this cementing system. The results obtained by different techniques (DTA/TG, X-ray diffraction, and SEM/EDAX) confirm that the activation conditions (in the range 700°-800°C and 2-5 h of retention) have a direct effect on the formation and evolution of hydrated phases. Low activation temperatures favor the CSH gels' formation, while at higher temperatures aluminates (C₄AH ₁₃) and aluminum silicate hydrates (C₄ASH₈, hydrotalcites) are predominant.