Hydration and physico-mechanical characterization of bottom ash-based cement
Résumé
The carbon footprint of cement is directly proportional to their clinker content. One of the solutions to reduce the environmental impact of the cement industry is the formulation of composite cement through the use of alternative materials to partially replace clinker. These materials must comply with certain standards (EN 197–1) and must not alter the engineering properties of cement. The aim of this study is to analyze the reactivity kinetics of coal bottom ash (CBA) powder in the cement matrix, and the impact of this addition on the physical and mechanical properties of cement. To do so, the hydration kinetics of the paste were monitored by thermal analysis (TGA) and X-ray diffractometry (XRD). The analysis was first carried out on pastes of lime mixture and CBA powder, and then on pastes of cement mixture and CBA. The physical characteristics (fineness and specific surface area) and main engineering properties (cement type, class of strength, setting time, heat of hydration, normal consistency, volume stability and shrinkage) of composite cement made from CBA were then studied. Three (03) composite cements containing 10 %, 15 % and 20 % by mass of CBA powder were studied. Paste monitoring by TGA and XRD showed that CBA powder has a slow reactivity, starting after 14 days of curing in the cementitious matrix. Characterization of the three composite cements shows that they are equivalent to CEM II/A 42.5 (for 10 % substitution) and 32.5 (for 15 % and 20 % substitutions). CBA increases water demand and setting time, but reduces the heat of hydration, autogenous and total shrinkage and volume expansion of composite cements. With a maximum CBA content of 10 %, the composite cement can be made without compromising early-age mechanical strength, which also offers advantages in terms of heat of hydration and shrinkage.