Class-C fly ash from coal as a partial substitute in cement-based paste and mortar design mix – A case in the Philippines

Abstract

An indirect way to minimize greenhouse emissions from the cement industry is partially substituting cement with coal fly ash (CFA). Despite CFA being widely studied, the quality, performance, and water requirements, when used in formulating paste and mortar, vary depending on the source. This study assessed CFA from a power plant in the Philippines as a partial substitute for cement. Paste and mortar mixture were designed to have varying CFA-to-binder ratios (CBR) and water-to-binder ratios (WBR). The effect of CBR and WBR on the consistency and workability of fresh paste and mortars were modeled, adopting multivariate non-linear regression to objectively assess the individual and interactive effects. Properties (compressive strength, density, and voids) of hardened mortar formulated with different CBRs but having normal consistency/workability were determined and assessed. Models generated could be used to estimate the WBR required for formulations to achieve normal consistency/workability. The water requirement for mortar formulation to have normal workability may be predicted based on the WBR for paste formulated to have normal consistency. Increased cement replacement with CFA improved the compressive strength, with replacement up to 20 wt% resulting in better performance than pure cement.