Seashell Versus Granite Aggregates: Comparative Evaluation of Concrete Properties

Concrete performance is strongly influenced by the type and quality of coarse aggregates, which govern key properties such as compressive strength, density, and durability. Conventional crushed granite aggregates provide reliable mechanical performance but are associated with environmental degradation and increasing material costs, particularly in coastal regions where alternative resources are abundant. Waste seashells, generated in large quantities from marine and seafood activities, present a potential sustainable aggregate substitute; however, direct comparative evidence between seashell and granite aggregate concretes remains limited. This study experimentally investigates the effects of crushed seashell and crushed granite aggregates on the compressive strength and density of concrete using a standardized 1:2:4 mix ratio and a constant water–cement ratio of 0.5. Concrete specimens were produced with varying levels of granite replacement by seashell aggregates and tested at curing ages of 7, 14, and 28 days. The results show that compressive strength increased with curing age for all mixtures, while increasing seashell content led to a gradual reduction in strength and density. The control mix containing 100% granite achieved the highest 28-day compressive strength of 18.11 MPa. A 20% replacement level attained a 28-day strength of 14.48 MPa, indicating acceptable performance for low- to medium-strength applications. Although higher replacement levels exhibited reduced early-age strength, concrete with 100% seashell aggregate showed notable late-age strength development, reaching 14.65 MPa at 28 days. Density decreased from 2561 kg/m³ for granite concrete to 2401 kg/m³ for full seashell replacement, accompanied by increased water absorption. These findings demonstrate that crushed seashell aggregates can serve as a viable and sustainable partial replacement for conventional granite aggregates, particularly in non-structural and lightweight concrete applications where reduced environmental impact is prioritized.