Effects of biochar addition on long-term behavior of concrete

In the context of circular economy, the production of innovative concretes that incorporate different kinds of waste material is gaining increasing interest among the researcher community, the regulatory agencies, and the policy makers. The rising awareness of the need of a sustainable development also in the building sector has indeed boosted the research towards the use, for concrete production, of waste material, which can be inserted as aggregate/cement replacement or as filler to improve specific properties of the mixtures. A waste material recently studied with this last aim is biochar, the solid by-product resulting from biomass pyro-gasification. This paper investigates the effects of biochar derived from forestry waste residues on the physical and mechanical performance of concrete, by adding it, during mixing, up to 5% by weight of cement. Density, workability, water absorption properties as well as compressive strength, flexural strength, and fracture energy were measured and compared to a reference concrete without biochar, focusing on long-term behavior. The results demonstrated a general improvement of mechanical properties and internal microstructure of concrete for an optimal biochar content of 2% by weight of cement.