Microstructural and physicochemical characterization, mechanical and durability performance with statistical evaluation of montmorillonite-impregnated burnt red soil bricks incorporating pyrolyzed coffee and tobacco biochars

The growing demand for sustainable construction materials has increased interest in utilizing agricultural waste as functional additives in fired clay products. However, limited information is available regarding the influence of pyrolysis temperature on the engineering performance, durability, and physicochemical characteristics of biomass-modified burnt red soil bricks. This study investigated the effects of pyrolyzed coffee grounds (PCG) and pyrolyzed tobacco grounds (PTG) produced at 300°C, 350°C, and 500°C and incorporated at replacement levels of 5%, 10%, 15%, and 20% into burnt red soil bricks containing 10% montmorillonite. Mechanical performance was evaluated through compressive, tensile, and flexural strength tests, while durability was assessed using water, chloride, and sulphur penetration measurements. Microstructural and physicochemical characterization was conducted using FTIR, XRD, DSC, Raman spectroscopy, and SEM analyses. Statistical significance was evaluated using analysis of variance (ANOVA) followed by Tukey’s honestly significant difference (HSD) post-hoc test at a 95% confidence level. The results demonstrated that biomass type, pyrolysis temperature, and replacement level significantly influenced both mechanical and durability properties (p