Valorization of engineered biochar to develop ultra-high-performance fiber-reinforced concrete with low carbon emission

This research introduces an innovative approach to developing carbon-negative Ultra-High-Performance fiber-reinforced Concrete (UHPC) by incorporating substantial quantities of biochar, both as a binder and as an aggregate, replacing up to 25% by weight of Ordinary Portland Cement (OPC) and quartz sand (QS). The study examines the impact of biochar on cement hydration processes, microstructure evolution, and various other performance metrics in the modified UHPC. Samples were formulated with 3% double-hooked steel fibers and biochar quantities ranging from 5 to 25% by weight as substitutes for OPC and QS. The investigation included assessments of changes in rheological properties, strength metrics, long-term shrinkage, resistance to sulfate attacks, freeze-thaw durability, microstructure analysis, and a cost-benefit evaluation. Test results indicated that biochar-incorporated samples exhibited up to a 20% increase in heat evolution by the end of the seventh day and plastic energy at 28 days that rose to 32.14% as compared to control samples in 20% biochar-augmented versions. Shrinkage reduction varied between 58 and 69% at 210 days for samples with 20% biochar. Specifically, the mix containing 20% biochar (G2-M5-BC-20) significantly improved the 90-day compressive and flexural strength by 8.9 and 9.3%, and 30.6 and 36.8%, respectively, while further inclusion of biochar showed no marked enhancement in performance metrics. The G2-M5-BC-20 mix also demonstrated excellent resistance to sulfate attacks and freeze-thaw cycles, exhibiting the least mass loss and highest residual compressive strength. An initial cost-benefit revealed that biochar-enhanced UHPC could offer compelling financial benefits. Given its mechanical behavior, potential for harmful CO2 emissions, and economic viability, the G2-M5-BC-20 mix emerged as the most promising formulation, potentially generating an overall profit of $36 per cubic meter.