Incorporation of high-volume coal ashes in terrazzo tiles for pavement: A comprehensive assessment of engineering performance, microstructure, sustainability, and potential applications

The depletion of natural sand and rising environmental concerns in construction call for alternative, sustainable aggregates. This study investigates the potential of coal bottom ash (CBA) as a fine aggregate replacement in terrazzo tile production, evaluating its mechanical performance, durability, microstructure, and environmental impacts. The compliance of terrazzo tile properties with national standards and proposed application domains was further examined. A ternary binder of Portland cement, fly ash, and ground granulated blast-furnace slag was used. Six mixtures (B00–B100) were prepared with 0–100% CBA replacement by volume. As a result, the 28-day flexural strength declined from 3.99 MPa (B00) to 3.28 MPa (B100). Meanwhile, compressive strength dropped from 26.54 MPa to 20.07 MPa. The B50 mix retained 91.5% of compressive and 92.0% of flexural strength, with only a 20% increase in water absorption and a 17.7% increase in abrasion loss compared to the control. Surface water absorption and microstructure analyses indicated increased porosity, reduced hydration products, and a pronounced qualitative reduction in portlandite-related diffraction peak intensities, together with a near-complete loss of ettringite in high-CBA mixes. Despite these declines, environmental indicators improved significantly. Total embodied CO 2 -eq decreased from 327 to 287 kg/m³ , and energy demand reduced from 2116 to 1532 MJ/m³ (B100), with B50 showing 6.0% CO 2 -eq and 13.8% energy savings. Furthermore, normalized sustainability metrics improved after 28 days, with B50 and B70 offering optimal eco-efficiency. These findings suggest that up to 50% CBA replacement can produce terrazzo tiles with acceptable mechanical and durability performance while enhancing sustainability. Therefore, it appears to be a viable laboratory-scale strategy for eco-efficient pavement (i.e., high-use pedestrian or light-traffic applications) and flooring materials. • Coal bottom ash (CBA) was used as a fine aggregate replacement in terrazzo pavement tiles. • Mechanical, durability, microstructural, and environmental effects of CBA were evaluated. • Higher CBA content reduced total embodied CO 2 -eq and energy demand. • An optimal CBA replacement level of up to 50% was identified for terrazzo tiles. • CBA is a viable and eco-efficient fine aggregate for terrazzo tile production.