Washed Mixed Recycled Coarse Aggregates as Natural Aggregate Replacement in Concrete for Seawall Blocks

Construction and demolition waste remains a major sustainability challenge, while the use of mixed recycled aggregates in structural concrete is still limited due to concerns over variability, water absorption, and durability. This study investigates whether washed mixed recycled coarse aggregate can partially or fully replace natural coarse aggregate in concrete for seawall block applications. The recycled aggregate was characterised and then upgraded through simple washing and grading to remove fines and contaminants. Concrete mixes incorporating 0%, 5%, 10%, 20%, 50% and 100% recycled aggregate replacement were produced and tested for workability, compressive strength, flexural strength, density, and water absorption under both tap water and saline curing conditions. The results demonstrate that washing significantly improves aggregate quality, enabling compressive strength comparable to the reference mix at replacement levels up to approximately 20%. Higher replacement levels led to reductions in workability, flexural strength, and density; however, performance remained within technically acceptable limits. Overall, the findings indicate that washed mixed recycled coarse aggregate is a viable material for seawall concrete, supporting more circular and sustainable use of construction and demolition waste in marine infrastructure.