Role of the inherent stability of Prosopis juliflora biochar in cementitious mortars under elevated temperature and acidic environments

This work examines whether the inherent inertness of Prosopis juliflora biochar can extend its known ambient benefits to cementitious mortars exposed to harsher conditions. Building on earlier reports that biochar is stable, carbon-rich, and largely inert under normal environments, the study evaluates purposely low dosages (0.1–0.6 wt.%) as a case study under combined thermal and chemical stress. After heating to 600 °C, biochar-modified mortars exhibited refined crack patterns, higher ultrasonic pulse velocity (1985 → 2260 m/s), and greater residual strength (57% → 64%). TGA indicated a higher bound-water loss, reflecting enhanced hydration and microstructural stabilization through nucleation effects. Under sulfuric acid exposure, biochar mixes showed slightly reduced mass loss (8% → 7%) and marginally improved strength retention (93% → 95%). These modest but consistent gains suggest improved durability and slower deterioration in chemically aggressive environments. SEM analysis further revealed increased compactness, higher crack tortuosity, crack-bridging features, and stable biochar morphology, all of which support the observed performance trends. Overall, the findings indicate that small, optimized biochar dosages can positively influence mortar behavior in harsh conditions, with the inherent stability of Prosopis juliflora biochar playing a key role in this response.