Carbonate-functionalized biochar: Transforming self-captured CO₂ into mortar innovation

This work innovatively transformed the biochar generated from the pyrolysis of Spent Coffee Grounds (SCG) and converted it into Calcium Carbonate (CC) by capturing CO₂ released during the pyrolysis process. Pristine biochar (PB) and Carbonate-functionalized biochar (CaB) were derived from SCG, while CaB-SCG was produced through a one-step process, where (Ca(OH)₂) reacted with SCG's emitted CO₂ and carbon to form CC. CaB-PB300 and CaB-PB400 are produced from a two-step process. Quantitative X-ray Diffraction (Q-XRD) revealed 36.3 wt%, 25.9 wt%, and 14.3 wt% CC formation for CaB-SCG, CaB-PB300, and CaB-PB400, respectively. The PB and CaB biochar, at 3, 6, 8, and 10 wt%, were then used as partial cement replacements to produce mortar blocks. The inclusion of PB up to 3 % and CaB up to 6 % increased the heat of hydration. CaB maintained better workability compared to PB, and CaB inclusion of less than 8 % made the mortar block more water-resistant. Adding PB300 and CaB biochar up to 6 %, and PB400 up to 3 %, increased compressive strength, where the highest strength improvement of 12.3 % was gained by 6CaB-SCG, and further addition of biochar reduced strength. In the CaB samples, the functionalized CC product not only reduced porosity but also reduced harmful air pores and increased capillary pores. This research advocates innovatively using carbonate-functionalized biochar for enhanced strength, aiding in expedited carbon neutrality goals. By repurposing waste materials and reducing carbon emissions, this work can help to lessen the environmental footprint of construction materials substantially.