Modeling and optimization of calcined bentonite replacement in the mechanical and durability properties of mortar

Abstract

Currently, pozzolanic materials are mostly recommended to improve the properties of cement composite materials and reduce environmental pollution, challenging the world owing to ordinary Portland cement (OPC) production. Bentonite is mostly available natural pozzolana, however, extensive studies conducted on other clays like kaolin and some studies reported that bentonite exists in a consolidated form which requires heating activation methods. Therefore, it is essential to investigate the properties of bentonite in detail for its sustainable use, and it is novel to model and optimize the optimum bentonite calcination temperature and time for the best performance replacement in mortar. Hence, the present study investigates the optimum bentonite calcination temperature, calcination time, and replacement dose for mortar strength and free lime using the central composite design-response surface method (CCD-RSM). The mortar was prepared by replacing the calcined bentonite with cement weight with different values of the factor variables, bentonite dose, calcination temperature, and calcination time. Durability tests were conducted after 56 days. Thus, the results indicate that the selected model of response variables for compressive strength and free lime were significant, accurate, reliable, and had excellent fitness to the experimental work. Hence, CCD-RSM predicted the optimum for independent factors of bentonite dose 19.99 %, calcination temperature 799.99 °C, and calcination time 135.04 min and experimentally validated, which improved the strength by 24.94% and reduced free lime by 3.08% compared to the control mortar, besides reducing CO2 emissions compared to OPC production, which requires 1450 °C. Furthermore, the optimized bentonite replacement parameters have highly enhanced durability in different environments such as water, acids, salt, and elevated temperature compared to the control mixture at the age of 56 days.