Areca nut husk biochar as a sustainable carbonaceous filler for cement: Pyrolysis temperature and its effect on characterization, strength, and hydration

This study addresses the gap in sustainable agro-based materials for cement by exploring locally available areca nut husk pyrolyzed into areca nut husk biochar (AB). The research investigated the effect of pyrolysis temperature (300°C, 400°C, and 500°C) on the characteristics of AB and its impact on cementitious performance. The study found that increasing pyrolysis temperatures led to lower yield, greater aromaticity, and increased surface area of AB. Fourier Transform Infrared Spectroscopy (FTIR) analysis showed decreased functional groups in AB at higher temperatures, confirming enhanced carbonization. Thermogravimetric analysis (TGA) revealed greater thermal stability of AB. X-ray diffraction (XRD) indicated a carbon-rich amorphous structure and crystalline graphite carbon formation in AB. Incorporating AB at 2 % into cementitious composites substantially increased the compressive strength compared to the control mortar. At 7 and 28 days, the compressive strength increased by 8 % and 12 % for AB 300, 16 % and 21 % for AB 400, and 27 % and 34 % for AB 500. This improvement was due to the micro filler effect of AB, which improved the compactness of the cementitious matrix. Hydration studies from TGA showed that the addition of AB accelerated early-stage hydration, with the degree of hydration increasing from 46 % (in control mix) to 48–53 % in AB blended mixes using Bhatty’s method. FTIR analysis demonstrated improved hydration of silicate phases and C-S-H formation in the presence of AB, supported by XRD analysis. AB blended mortar reduced the CO₂ equivalent emission by 22 % compared to the control mortar attributed to its carbon sequestration capacity. These results highlight the potential of AB as a sustainable carbonaceous filler for cementitious composites, offering an environmentally friendly option for future research in construction materials.