The global demand for construction materials has led to significant environmental challenges, primarily due to the high carbon emissions of cement production. In a study published in Buildings, researchers Merve Esen Tanrikulu and Tuba Demir investigated the potential of almond shell biochar (ASB) and silica fume (SF) as supplementary cementitious materials to develop more sustainable concrete. By utilizing agricultural waste as a partial substitute for cement, the research aims to support the circular economy and achieve net-zero climate targets.

A critical finding of the study is that the combination of 6% ASB and 10% SF (the ASB6SF10 series) yielded the most favorable mechanical properties. Compressive strength tests revealed values of 44.2 MPa after 28 days of curing for this optimal mix. This improvement is attributed to the pozzolanic activity of the waste materials, which facilitates the formation of calcium silicate hydrate (C-S-H) gel, the primary binding component that increases structural strength.

The study utilized the maturity method to estimate concrete strength at early ages by monitoring temperature history. Monitoring showed that the ASB6SF10 series reached the highest temperature values, indicating accelerated hydration reactions and efficient C-S-H gel formation. This non-destructive testing provides a reliable way for construction teams to determine safe formwork removal times, leading to significant savings in project duration and labor costs.

Microstructure analysis using scanning electron microscopy (SEM) confirmed that the addition of ASB and SF creates a significantly denser concrete structure. While reference concrete often contains pores and ettringite formations that can weaken the material, the ASB-enhanced series showed that biochar serves as an effective filler. This densification results in higher compactness and lower 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 (as low as 10% for the optimal series), which is a key indicator of high-quality, durable concrete.

From an environmental standpoint, the researchers found that replacing cement with ASB and SF significantly reduces the carbon footprint of concrete production. Because cement production is responsible for approximately 7–8% of global carbon dioxide emissions, even small substitutions with waste materials have a major impact on sustainability. The study highlights that transforming almond shell waste into a high-value activator for low-carbon concrete provides ecological gains while solving the problem of agricultural waste storage.

Ultimately, this research suggests that a 6% ASB and 10% SF ratio is the most effective blend for producing normal-strength, eco-friendly concrete. By adopting these sustainable practices, the construction industry can decrease its dependence on traditional cement and move closer to international climate goals. Future developments may involve exploring biochars with even higher amorphous silica content to further push the boundaries of eco-efficient concrete performance.

Source: Tanrikulu, M. E., & Demir, T. (2025). Efficient Utilization of Almond Shell Biochar and Silica Fume for Normal Strength Concrete to Develop Eco-Friendly Concrete. Buildings, 16(1), 112.