Coal Bottom Ash as Supplementary Cementitious Material: Optimizing Reactivity Through Particle Grinding

The shortening tendency of fly ash (FA), together with a reduction in the clinker factor of Portland cement, has driven the search for alternative supplementary cementitious materials (SCMs). Coal bottom ash (CBA) is a byproduct of coal combustion in thermal power plants and has the potential to be used as an SCM. This work assessed the optimization of CBA’s performance as an SCM through particle grinding. Reactivity (R3 test), rheological, and compressive strength tests were conducted, in addition to a thorough characterization of CBA. The results showed that increasing the grinding time progressively increased the reactivity of CBA (R3 heat release), matching the reactivity of FA with 10 min of grinding. Compressive strength tests demonstrated that grinding the CBA for 10 min led to an equivalent performance compared to FA, while increasing the grinding time did not result in additional strength gains. Rheological tests showed that CBA incorporation increased the yield stress and viscosity of pastes (associated with finer and more angular CBA particles); about 40–45% more superplasticizer (SP) was required for CBA-containing pastes to reach a target yield stress compared with FA-containing samples. Overall, properly grinding CBA allowed for obtaining an equivalent reactivity and strength performance to FA, but more SP was required to obtain the same workability.