Optimization of pyrolysis conditions for stubble waste-derived biochar in mortar: Enhancing mechanical performance, durability, and carbon sequestration.

The construction industry significantly contributes to global carbon emissions, primarily owing to cement production, while the open-field burning of agricultural stubble waste poses severe environmental concerns. This study explores the valorization of biochar produced from rice stubble waste as a partial substitute for cement in mortar, with process optimization conducted through response surface methodology (RSM). The key parameters such as pyrolysis temperature (450-550 °C), residence time (60-120 min), and biochar concentration (5-10%) were altered to evaluate their effects on mechanical performance, durability, microstructural properties, and CO2 uptake potential. Optimal conditions led to enhancements in 28-day compressive and flexural strengths by 30.5% and 31.4%, respectively, as well as reductions in water absorption and void volume by 19.7% and 19.0%. Microstructural studies revealed denser and more refined pore structures, validating improved mechanical and durability characteristics. Thermogravimetric analysis indicated improved carbonation efficiency, with CaCO3 content and CO2 uptake increasing by 24.04% and 10.59%, respectively. The ANOVA results confirmed the reliability and statistical significance of the developed models, with p-values below 0.05 and R2 values exceeding 98% for all assessed parameters. This study emphasizes biochar's potential to simultaneously reduce cement consumption and mitigate stubble waste, presenting a sustainable approach to low-carbon construction practices.