Pyrolysis upcycling of sugarcane filter cake into engineered biochar for low-carbon cement composites: Process optimization via RSM

The sustainable management of agro-industrial waste is a great challenge for the global economy. This research investigates the upcycling of sugarcane filter cake into an engineered biochar for use as a supplementary cementitious material (SCM) in low-carbon pavements. Response Surface Methodology (RSM) was implemented to systematically optimize pyrolysis temperature (300 - 700°C), residence time (10 - 50 min), and nitrogen flow rate (0.2 - 0.4 L/min) to resolve the trade-off between biochar yield (BY) and pozzolanic reactivity. The optimal conditions of 400°C, 24 min, and 0.3 L/min gave a high BY of 78.45%, while concentrating essential pozzolanic elements (12.02% Ca and 9.80% Si). This targeted mineral enrichment, corroborated by FESEM-EDS analysis, significantly enhanced the biochar's microstructural morphology and inherent cementitious reactivity. Consequently, replacing 5% of ordinary Portland cement with this optimized biochar induced a robust micro-filler effect and promoted hydration within the cement matrix. This 5% substitution maintained a high compressive strength (>40 MPa) comparable to the control, satisfying TIS requirements for paving blocks. Although higher dosages led to increased porosity and water absorption, the 5% blend remained durable and within acceptable limits. These results indicate that filter cake biochar is a promising and environmentally friendly SCM, which provides a solution to the problem of waste disposal and the creation of low-carbon construction materials.