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

Author name : Aboelnaga yosri mahmoud ahmed

Publication Date : 2025-03-13

Journal Name : Journal of Sustainable Cement-Based Materials

Abstract

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 theimpact of biochar on cement hydration processes, microstructure evolution, and various other performance metrics inthe modified UHPC. Samples were formulated with 3% double-hooked steel fibers and biochar quantities rangingfrom 5 to 25% by weight as substitutes for OPC and QS. The investigation included assessments of changes inrheological 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 samplesexhibited up to a 20% increase in heat evolution by the end of the seventh day and plastic energy at 28 days that roseto 32.14% as compared to control samples in 20% biochar-augmented versions. Shrinkage reduction varied between58 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 alsodemonstrated excellent resistance to sulfate attacks and freeze-thaw cycles, exhibiting the least mass loss and highestresidual compressive strength. An initial cost-benefit revealed that biochar-enhanced UHPC could offer compellingfinancial 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 percubic meter

Keywords

Biochar; carbon emission; biochar aggregate; plastic energy; TGA analysis; XRD analysis1. IntroductionUltra-high-performance concrete (UHPC) is an advancedconstruction material known for its exceptional strengthand durability [1,2]. Unlike traditional concrete, UHPCcomprises carefully selected constituents, including cement,silica fume, fine quartz sand, and fibers [3]. This combin-ation results in a densely packed microstructure and out-standing mechanical properties. The hardened UHPC hasa deficient (<2%) void content; these tiny voids areeffectively occupied by incorporating a significant quan-tity of silica fume, serving as a pozzolanic and a fillercomponent [4–6]. This leads to greatly accelerated hydra-tion and exceptionally high strength levels within the firstday [7,8]. However, UHPC’s low water-to-binder (w/b)ratio, a key factor behind its strength, can also lead to asignificant challenge: shrinkage. Shrinkage occurs asUHPC cures and water evaporates from its dense matrix