Sustainable utilization of foundry reclamation fines in construction materials

Mechanical reclamation of waste foundry sand (WFS) generates approximately 20% clay–sand fines (CSF), an ultra-fine by-product (10–50 µm) that remains largely unutilized and presents a growing environmental challenge for the foundry industry. This study establishes a comprehensive valorization pathway for CSF as a functional replacement material in fired clay bricks, structural concrete, and interlocking paver blocks, integrating physico-chemical characterization with multi-scale performance evaluation. CSF incorporation at 25–100% replacement levels significantly modified microstructural development, pore architecture, and mechanical behavior. Bricks containing 25% CSF achieved the highest compressive strength (42.88 kg/cm 2 ) with controlled water absorption (22.88%) and refined pore structure, satisfying IS 1077 requirements. In cementitious systems, CSF exhibited pronounced micro-filler and packing effects, producing an optimum compressive strength of 32.55 N/mm 2 in M20 concrete and 31.55 N/mm 2 in M30 paver blocks at moderate replacement levels. BET analysis confirmed progressive pore refinement and interfacial transition zone densification governing performance. At higher CSF contents, excessive fines and elevated loss on ignition induced matrix weakening and strength reduction. The results demonstrate that CSF functions as a high-performance engineered fine material, enabling substantial landfill diversion and resource conservation. This work provides a scalable, low-carbon circular-economy strategy for transforming reclaimed foundry fines into durable construction products. • CSF at 25% in bricks achieved 42.88 kg/cm 2 compressive strength meeting IS 1077. • Concrete with 30% CSF reached 32.55 N/mm 2 compressive strength at 28 days. • M30 paver blocks with 20–30% CSF obtained 31.55 N/mm 2 compressive strength. • CSF improved packing density due to 10–50 µm particle size and 14 m 2 /g surface area. • Utilization of CSF diverts 20% foundry waste from landfills supporting circular economy.