Biochar (BC), a byproduct of agricultural waste pyrolysis, shows potential as a sustainable substitute material for ordinary silicate cement (OPC) in concrete production, providing opportunities for environmental sustainability and resource conservation in the construction industry. However, the optimal biochar dosage and fineness for enhancing concrete performance are still unclear. This study investigated the impact of these two factors on the mechanical and durability properties of biochar concrete. Compressive and flexural strength, carbonation resistance, and chloride ion penetration resistance were evaluated by varying biochar dosages (0%, 1%, 3%, 5%, 10%) and fineness dimensions (44.70, 73.28, 750, 1020 μm), with the 0% dosage serving as the control group (CK). The results showed that the addition of 1–3 wt% of biochar could effectively reduce the rapid carbonation depth and chloride diffusion coefficient of concrete. The compressive and flexural strength of BC concrete initially increased and then decreased with the increase in biocarbon content, BC with a fineness of 73.28 μm having the most significant effect on the mechanical strength of concrete. At the dosage of 3 wt%, BC was found to promote the hydration degree of cement, improving the formation of cement hydration products. These findings provide valuable insights for the development of sustainable and high-performance cement-based materials with the appropriate use of biochar as an additive.

Biochar (BC) is a porous carbon formed by pyrolysis of biomass at high temperatures under anoxic conditions. The use of pulverized BC as a cementitious materials mixture has recently gained research momentum because this usage can lock BC in inert materials and reduce cement consumption simultaneously. This paper presents a review on the use BC particles as an additive or cement replacement in cementitious composites over the last few decades. It comprehensively reviews and discusses the physicochemical properties of BC, as well as the influence of BC on the hydration kinetics, workability, physical properties, mechanical properties, and durability of mortar or concrete. The replacement of cement with 1%–3% BC, in weight, decreases the permeability and increases the mechanism strength of cementitious composites. The properties of the BC-cement composites is closely related to the carbonaceous particle fineness, feedstock, pyrolysis temperature, and treatment method of the BC. Further research is expected to discover BC-based cementitious material for preparing a specific BC for a specific use as cementitious mixture.

The utilization of agricultural waste, specifically biochar (BC), as an alternative material to conventional Portland cement offers substantial potential for enhancing sustainability within the construction industry. This study investigates how variations in BC particle size and content affect the properties of cement mortar using Response Surface Methodology (RSM). By manipulating BC’s content and particle size in the mortar mixture and analyzing the data with RSM, this study establishes response surface models to predict the relationship between BC characteristics and cement mortar strength. The results demonstrate that the optimal combination for enhancing the mechanical performance of the mortar is achieved when BC particles have a median particle diameter of 51.08 μm and a content of 2.69% of the mixture. Additionally, utilizing scanning electron microscopy (SEM), it is revealed that BC serves as a nucleation site for cement hydration, thereby inducing a more compact and dense microstructure within the cement mortar. Furthermore, BC particles contribute to enhancing the interfacial transition zone between the cement paste and aggregate, leading to increased compressive strength and fracture toughness of the mortar while simultaneously curbing crack propagation.