Blended cement and mortar with various low-calcium ground coal bottom ash content: Engineering characteristics, embodied carbon and cost analysis

Abstract

Coal bottom ash (CBA) can be broadly divided into two main categories, with high and low calcium, based on the calcium oxide content. While high-calcium CBA has been established as a suitable substitute material in slag-ternary blended cement, the feasibility of low calcium for this use remains unexplored. This study aimed to assess the influence of using various contents of low-calcium ground CBA (GCBA) and ground granulated blast-furnace slag (GGBS) as supplementary cementitious materials on the properties of GCBA binary and GCBA–GGBS ternary blended cement and mortars. The present work combined low calcium GCBA at different cement replacement levels between 5% and 25% with ordinary Portland cement (OPC) and GGBS to produce ternary and binary blended mortar. The sand-to-binder and water-to-binder ratios were held constant at 3.0 and 0.5, respectively. The results showed that up to 25% of GCBA in binary or ternary blended mortar increased from 20 to 35 min and from 5 to 20 min for the initial and final setting times, respectively. In addition, the binary or ternary blended mixture with up to 25% GCBA demonstrated a 10–20 mm higher flow diameter than the control. The blended cement's lime saturation factor (LSF) was lower than 1.0, and the value was reduced from 0.70 to 0.45 with increased cement replacement from 5% to 25% with GCBA. Moreover, the binary and ternary blended mixtures, including 10–15% GCBA, exhibited up to 6.7% greater compressive strength than the control. In addition, the ternary blended mortar containing GCBA and GGBS had greater compressive strength than the GCBA binary blended mixture. Thus, the inclusion of 5–15% GCBA increased the mechanical strength of the blended mortar. However, 20–25% of GCBA resulted in a decrease in strength from the optimal level. Thus, the blended mortar with 15% cement substitution with GCBA exhibited the greatest strength performance. © 2024 Elsevier Ltd