Characterization of the physicochemical and functional properties of clay-based construction materials with a neutral carbon footprint using recycled pistachio shell waste

Abstract

This study explores the recycling of pistachio shell waste in producing eco-friendly, non-fired clay bricks, aiming for both economic and ecological benefits. The pistachio shells were sourced from the Taounate region in northern Morocco, and the clay used was extracted from Oulad Azam, in the same region. X-ray analysis of the soil revealed a high Illite clay content with around 40 % SiO₂, making it suitable for construction. Brick samples were made with varying pistachio shell content (0 %–20 %, including intermediate levels such as 1 %, 3 %, 5 %, 7 %, and 15 %) and sizes: small (δ < 1 mm), medium (1 mm < δ ≤ 3 mm), and large (δ > 6 mm). Physical (porosity, density), mechanical (compressive strength), and thermal (conductivity) properties were evaluated. Results showed lightweight bricks, with densities below 1.75 g/cm³, linked to higher porosity for smaller additive sizes. Microscopic observations confirmed reduced porosity for finer additive sizes (δ ≤ 1 mm), contributing to enhanced performance. Compressive strength improved by 8 % and thermal conductivity by 23 % with smaller grains. The strength of the bricks generally decreased with increasing additive content, while insulation improved significantly. However, there was a trade-off between insulation and strength. The optimal balance was found at additive dosages of 7 %, 8 %, and 9 % for large, medium, and small grains, respectively, yielding bricks with better performance than conventional industrial ones. These results suggest that the valorization of local agricultural waste contributes positively to both sustainable construction and the local economy.