Mechanical Performance of Pyrolysis Biochar-Enhanced Sustainable Concrete

The mechanical properties were investigated of high-strength concrete with a water-to-binder (w/b) ratio of 0.5, utilizing a superplasticizer to control workability. Biochar from sugarcane bagasse (BCS) was used as a partial cement replacement at levels of 1%, 3%, 5%, or 7% by weight. The biochar was produced using the pyrolysis process, involving thermal decomposition of biomass under limited oxygen conditions. Testing was conducted on 100 × 200 mm cylindrical specimens and 100 × 100 × 350 mm beams. Based on the experimental results, the 1% BCS replacement was optimal for improving concrete strength. This improvement was attributed to the finely ground biochar particles (10–30 μm), having a size comparable to cement particles, thereby enhancing packing density. Furthermore, the porous structure of the biochar facilitated internal curing by retaining water and gradually releasing it to promote long-term hydration. The fresh concrete slump was regulated according to ASTM C143, and mechanical properties (compressive strength, splitting tensile strength, and flexural strength) were evaluated. After 28 days of water curing, specimens with the 1% BCS had increased compressive, tensile, and flexural strengths by 7.45%, 5.85%, and 2.5%, respectively. However, when the BCS replacement exceeded 1%, the porosity and void content within the concrete matrix increased. Excessive biochar led to particle clumping and poor dispersion, resulting in large air pockets and interconnected gaps around biochar clusters. These voids acted as weak points that hindered load transfer and served as sites for crack initiation, causing a continuous decline in mechanical performance. This study established a sustainable pathway for the valorization of sugarcane bagasse into an engineered supplementary cementitious material, demonstrating dual benefits in carbon sequestration and mechanical performance optimization for sustainable high-strength concrete.