A comprehensive review of biochar-modified concrete: Mechanical performance and microstructural insights

With the world's population steadily increasing and the demand for improved urban infrastructure increasing, there is expected to be a corresponding increase in greenhouse gas emissions from the construction sector. The current pace of CO2 emissions poses a threat of pushing the planet beyond a critical threshold, potentially leading to catastrophic impacts on the climate. The Earth's capacity to naturally offset the effects of CO2 emissions within the carbon cycle has reached its limit. Adopting technologies that capture and store CO2 generated from practices such as construction and building is of utmost importance. The most practical method is to identify efficient waste resources that can be seamlessly incorporated into the production process of cement-based materials. The possible integration of biochar as an effective CO2 absorptive material and used in construction materials shows promise due to its unique properties and sustainable benefits. This review article comprehensively analyses biochar's source and properties to evaluate its effectiveness as a cement substitute in cement-based materials and concrete. The review begins by exploring the different methods utilized in biochar production, focusing on how they influence its chemical properties. This review assesses the properties of fresh and hardened cement mortars and concrete, incorporating biochar while investigating their microstructural characteristics. In conclusion, biochar is primarily composed of carbon, with percentages ranging from 19.67 % to 76.60 %. In its initial state, concrete incorporating biochar displayed densities ranging from 2245 to 2330 kg/m³. Upon reaching the hardened state, these values were observed to be 2013 and 2195 kg/m³, representing the minimum and maximum densities, respectively. The tensile strength exhibits variability, ranging from 1.9 to 4.9 MPa, with BC content ranging from 0.1 % to 5.0 %. Regarding flexural strength, there is a variation from 2.1 to 8.8 MPa, corresponding to changes in BC content ranging from 0.25 % to 10 %. Moreover, there is an increasing need for sustainable concrete with low carbon emissions, incorporating carbon-negative elements to improve its performance.