In recent years, there has been a concerning surge in CO₂ emissions, with the construction and materials production sectors standing out as significant contributors to greenhouse gas pollution. To tackle this pressing environmental challenge, architectural design and civil engineering are actively pursuing strategies to mitigate their carbon footprint. These initiatives include adopting eco-friendly construction materials with reduced toxicity, rigorous energy management practices across the entire life cycle of structures, and incorporating innovative materials like biochar. Biochar is a carbon-rich byproduct generated through controlled thermochemical processes, such as pyrolysis or gasification, that stands out for its remarkable capacity to extract energy from processed biomass while delivering substantial environmental advantages. This study examines the use of biochar as a filler in cement-paste and mortar, as well as its influence on mechanical properties. In the case of cementitious pastes, results show that small amounts of biochar (1-2-5% by weight of cement) can improve the compressive and flexural strength, as well as fracture energy, thus generating a more tortuous crack path that increases the final surface area. In mortar specimens, the biochar influence does not show similar patterns or characteristics as the cement-paste in flexural and compressive strengths; nevertheless, biochar particles improve the toughness.

Concrete is one of the most widely used materials in the world. Still, its production processes, energy consumption, and high use of raw materials make it one of the most environmentally harmful materials. This study aims to enhance the sustainability of concrete by reducing the amount of binder and incorporating secondary materials into the cementitious matrix. The binder reduction is achieved by using a foaming agent that creates a microporous matrix, significantly decreasing the volume of cement in the material. Additionally, reinforcing the material with sheep wool fiber not only improves its mechanical properties but also gives a new purpose to a commonly discarded secondary material. The research specifically seeks to identify the most effective treatments for sheep wool fiber (including non-treated, salt-treated, lime-treated, NaOH-treated, and surfactant-treated fibers), as well as the optimal fiber length (6, 12, and 20 mm) and content (4.5, 9, and 15 kg/m³) for ultralightweight foamed concrete in terms of mechanical strength. The findings demonstrate excellent compatibility between wool fibers and ultralightweight foamed concrete, with fiber-reinforced samples showing up to a 60% increase in flexural strength and up to a 50% increase in compressive strength. Among the various fiber treatments evaluated, surfactant-treated fibers yielded the best results.