Comparative Assessment of Sugarcane Bagasse and Sawdust Ashes as Supplementary Cementitious Materials in Lime-Based Binders

The high energy demand, rising cost, and environmental impact of Ordinary Portland Cement (OPC) production have intensified the search for low-carbon alternatives, particularly in low- and middle-income countries. Lime–pozzolana binders incorporating agricultural waste ashes are promising, yet their development is often guided by strength-based evaluation alone, limiting mechanistic understanding. This study presents a systematic comparison of sugarcane bagasse ash (SCBA)–lime and sawdust ash (SDA)–lime binders by linking early-age pozzolanic reactivity with material characteristics and mortar performance. SCBA and SDA were produced under controlled calcination (600–700°C) and characterized for chemical composition, mineralogy, particle size, and surface area. Pozzolanic activity was quantified using an electrical conductivity method, and its relationship with bulk density, water absorption, and 28-day compressive strength was evaluated and benchmarked against OPC mortars. SCBA exhibited a high combined SiO₂ + Al₂O₃ + Fe₂O₃ content (86.6%) and predominantly amorphous structure, while SDA showed lower oxide content (23.16%) but higher surface area, resulting in faster early-age reactivity. Despite this, SCBA–lime mortars achieved higher 28-day compressive strengths, although both systems met requirements for low-rise masonry. By directly correlating pozzolanic reactivity with ash composition and mechanical performance, this study advances understanding of structure–property relationships in lime–pozzolana binders and provides performance-informed guidance for selecting locally available agricultural ashes as sustainable alternatives to OPC.