PERFORMANCE OF CONCRETE WITH RECYCLED CONCRETE AGGREGATES AND CEMENT KILN DUST

Abstract

The rapid growth in infrastructure development has posed significant environmental challenges, particularly through the depletion of natural resources and the generation of construction and demolition waste (CDW). This study explores the use of recycled concrete aggregates (RCA) derived from CDW as a sustainable alternative to natural aggregates, aiming to reduce environmental impact by lowering landfill waste, carbon emissions, and the demand for non-renewable resources in construction. Concrete production also releases considerable CO₂ and generates a by-product known as Cement Kiln Dust (CKD) from unreacted and partially calcined raw materials. This research examines the potential of RCA and CKD in enhancing the sustainability of concrete by investigating their effects on physical, mechanical, and durability properties. Mixtures were prepared with RCA replacing natural coarse aggregate at levels of 0%, 25%, 50%, 75%, and 100%, and CKD replacing ordinary Portland cement at 10% and 20%, all at a water-to-cement ratio of 0.54. Compressive strength, splitting tensile strength, and durability (measured by water absorption and acid resistance) were tested on the RCA-CKD concrete. Fresh properties were assessed through slump flow and compaction factor tests. Concrete cube specimens (100 mm³) were used for compressive and durability tests, while cylindrical specimens (200 mm diameter x 100 mm height) were used for tensile strength tests. Results showed that at 56 days, the control concrete achieved the highest compressive strength of 30.68 N/mm², while the 100% RCA with 20% CKD replacement mix reached 24.05 N/mm². Water absorption results indicated all RCA mixtures were within the recommended 10% limit (Neville, 2011). These findings suggest that RCA can entirely replace natural aggregates, and CKD can replace up to 20% of cement, without significantly compromising the target strength of 25 N/mm².