Performance optimization and carbon reduction potential of bamboo biochar fine aggregates for sustainable geopolymer mortars

This study evaluated the feasibility of using bamboo biochar as a fine aggregate in geopolymer mortar and investigated its combined effects on workability, mechanical strength, drying shrinkage, pore structure, and carbon emissions. Bamboo biochar was used to replace sea sand at rates of 5 %, 10 %, and 15 %, and a pretreatment method combining humidity conditioning with fly ash coating was applied to enhance aggregate performance. Results indicated that untreated bamboo biochar reduced mortar flowability and compressive strength while increasing drying shrinkage with higher replacement levels. After pretreatment, fine particles exhibited improved interfacial bonding and dispersion, with flowability increasing by up to 25 %, while the compressive strength of MT#100 at 10 % replacement remained about 16 % lower than the control mix. The pore structure was densified, and some biochar pores were filled with gel products. Life cycle assessment revealed that the 5 % replacement mix (MBC-5 %) offered the most balanced performance. It reduced the global warming potential by about 28 %, while keeping cumulative energy demand increased below 8 %. The study shows that through simple material optimization, bamboo biochar can be effectively integrated into geopolymer systems, reinforcing their potential for sustainable and low-carbon construction.