Valorization of calcined Egyptian marble waste as a reactive CaO additive for fortifying alkali-activated slag cement

Abstract Egypt’s thriving marble industry produces extensive waste marble powder (WMP) amounts. Recycling plentiful waste safely and effectively is a key national concern, as improper disposal poses a serious threat to the environment. This study addressed this challenge by exploring a new method to produce CaO from WMP by appropriate calcination (CWMP), which can be used as an effective additive for alkali-activated slag (AAS) cement. The CaO extracted from WMP (CWMP) was introduced into AAS cement at varying levels, ranging from 2.5 up to 15%, in 2.5% increments, by weight, as a partial slag replacement. Multiple assessments were conducted to evaluate the influence of CWMP (i.e., CaO derivative from WMP) on specific features of AAS cement. Superior analytical techniques were utilized to achieve a deeper comprehension of the results. The findings revealed a decrease in both flowability and setting time with including CWMP. As the CWMP amount increased, flowability decreased, and setting time became shorter. The introduction of CWMP up to 10% improved performance, with the optimal at 7.5%, improving compressive strength and the ability to withstand environmental conditions. Specifically, the optimal 7.5% CWMP addition increased the 28-day compressive strength by 22.96% and reduced the strength loss after durability cycling from 14.43 to 10.93%. Additionally, the persistent issue of drying shrinkage within this system could also be alleviated by including CWMP up to 10%, particularly at 7.5%. Amounts of CWMP over 10% showed detrimental effects. Repurposing WMP as a CaO source not only manages a problematic waste stream but also saves CaO produced from natural limestone.