Utilization of engineered biochar as a binder in carbon negative cement-based composites: A review

With the rising global population and an increasing demand for enhanced built environments, the construction industry faces a critical challenge with rising greenhouse gas emissions, particularly carbon dioxide. Approaching a tipping point, these emissions could contribute to irreversible climate change, surpassing the Earth's capacity to neutralize them through the natural carbon cycle. In response, the imperative adoption of technologies capable of capturing and sequestering CO2 becomes crucial, especially in industries like construction and building. This urgency is essential to significantly reduce the carbon footprint of cement -based material production and induce positive climate change. This review emphasizes consolidating information from recent studies on biochar derived from agro-sources used as an admixture in cement -based applications. It delves into the origins of biomass and the methods employed in its production while highlighting the advantageous impacts of biochar on carbon capture for various properties of cementitious applications. Moreover, biochar, valued for its inexpensive, carbon-efficient, and sustainability gains, has increasingly been applied in cementitious materials. This study provides an exhaustive review of the impact of engineered biochar in the development and performance of carbon-negative cement -based composites, focusing on durability, mechanical, fresh, and microstructural characteristics, as well as carbon-sequestration capacity. Notably, biochar enhances hardened biochar-cement composites' physical, durability, and microstructural characteristics, with an optimal cement replacement of 1-2% wt. Adding biochar further improves endurance against permeability, shrinkage, sulfate attacks, and chloride-induced corrosion. Biochar's potential to reduce concrete permeability is consistent across different pyrolysis temperatures. Positive effects on durability (up to 5% by wt.) are ascribed to Improved hydration and enhanced physical filling, leading to a more compact microstructure, which hinders the penetration of ions and water.