Experimental investigations on NaOH-treated crumb rubber fly ash bricks

This study investigated the feasibility of partially replacing fine aggregates with crumb rubber (CR) in fly ash bricks and examines the influence of sodium hydroxide (NaOH) treatment on their performance. Fly ash bricks were produced with 3–25% CR replacement by volume, using both untreated (UM) and NaOH-treated (TM) rubber. Mechanical, durability, and microstructural properties were assessed through compressive and flexural strength tests, water absorption (WA), initial rate of water absorption (IRA), efflorescence testing, scanning electron microscopy (SEM), and X-ray diffraction (XRD) analysis. Results indicate that up to 12% CR replacement caused no significant loss in compressive or flexural strength, with TM bricks consistently outperforming UM bricks. NaOH treatment slightly reduced WA (0.65–2%) and marginally improved IRA values, although SEM revealed more voids in TM specimens at higher CR contents. XRD analysis confirmed no major crystalline phase changes between TM and UM bricks. Limited difference is observed in cost and global warming potential relative to conventional clay bricks. The findings suggest that NaOH-treated CR can be used in fly ash bricks at replacement levels up to 12% without compromising mechanical performance, offering a viable and sustainable alternative for masonry applications.