Sustainable Use of Coal Combustion Bottom Ash as A Fine Aggregate in Normal-Strength Concrete Production

Abstract

The construction industry’s heavy reliance on natural sand and cement contributes significantly to environmental degradation, driving the need for more sustainable materials. One potential solution is the use of coal combustion bottom ash (BA), a waste by-product from coal-fired power plants, as a replacement for fine aggregates in concrete. This study investigates the use of bottom ash (BA) as a partial replacement for natural sand (0–100%) in normal-strength concrete through a comprehensive experimental program. Concrete mixtures incorporating different BA replacement levels were evaluated, focusing on the combined effects on workability, water absorption, porosity, and ultrasonic pulse velocity. Results revealed that while increasing the w/b ratio improved workability, it reduced compressive strength, with the control mixture WB36 (w/b = 0.36) achieving 30.87 MPa at 28 days. Notably, BA30 (30% BA) demonstrated a 4.5% increase in strength, while BA100 (100% BA) caused a significant 43.5% decline. Higher BA content also led to increased water absorption and porosity, with BA100 exhibiting a 122.75% increase in water absorption. Additionally, the study provides a quantitative evaluation of the environmental benefits, showing that BA30 reduces CO₂ emissions by 2.34%, while BA100 achieves a 10.55% reduction. This research demonstrates that, by carefully balancing BA content, concrete can achieve significant sustainability gains, offering a novel approach to waste valorization in construction. The findings identify BA30 as an optimal mix, offering a balanced trade-off between engineering performance and environmental impact, supporting its potential application in sustainable concrete production.