Evaluating the performance of oyster shells as sustainable coarse aggregate in concrete grade 25 (C25) production

Abstract

This study assesses concrete using crushed granite (CC) and oyster shells (OS) as aggregates. Grading analysis confirmed well-graded distributions, with sand's fineness modulus (2.52) meeting British Standard (BS 812-103.1). OS concrete exhibited a higher water-cement ratio (0.67 vs. 0.55 design) due to greater water absorption (1.8% vs. 0.4% for CC). However, it was still within the BS 8500:1 limit. Crushed granite achieved a 70 mm slump, while OS recorded zero. This is attributed to its semi-elliptical shape, reducing grout availability. Both materials met the aggregate impact value (AIV), Los Angeles Abrasion value (LAAV), and specific gravity standards. At 28 days, compressive strength was 25.7 MPa for CC and 17.3 MPa for OS. The oyster shell failed to meet the 25 MPa design strength even after 36 days of curing. This could be attributed to the geometry and water-cement ratio limiting its performance, and optimization of the concrete is required.