Lin, et al (2025) Durability of biochar-cementitious composites incorporating crystalline admixture in chloride and sulphate environments. Construction and Building Materials. https://doi.org/10.1016/j.conbuildmat.2024.139554

A recent study investigates how adding waste wood biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More (WWB) and crystalline admixtures (CA) to cementitious composites improves their durability against chloride and sulfate exposure, common in coastal environments. These innovations promise to enhance the lifespan of concrete structures while promoting sustainability.

The research evaluated six concrete mixes with varying levels of CA and WWB over 156 days, immersing samples in water, sodium sulfate (Na₂SO₄), and sodium chloride (NaCl) solutions. Key findings include:

1. Reduced Water Adsorption: Both CA and WWB decreased water uptake by densifying the concrete’s microstructure, reducing porosityPorosity of biochar is a key factor in its effectiveness as a soil amendment and its ability to retain water and nutrients. Biochar’s porosity is influenced by feedstock type and pyrolysis temperature, and it plays a crucial role in microbial activity and overall soil health. Biochar More. This was observed as a 6–7% improvement in strength under water exposure.

2. Sulfate Resistance: Samples with CA showed a 14–16% reduction in sulfate absorption at 156 days, while WWB additions achieved up to 18% reduction. CA enhanced sulfate resistance by forming crystalline deposits, while WWB provided additional hydration sites.

3. Chloride Resistance: Chloride penetration was reduced by 15–18% with CA and up to 20% with WWB. The biochar’s microstructure helped bind chloride ions, limiting their diffusion.

Despite initial improvements, long-term immersion revealed cracks due to continued sulfate and chloride exposure. However, composites with CA and WWB maintained higher strength compared to control samples.

This study highlights the potential of combining CA and biochar to develop durable, sustainable construction materials. Further research is needed to explore long-term durability and other properties like shrinkage and carbonation.