Performance assessment of mechanical properties of green normal strength concrete produced with metakaolin-cement coated recycled concrete aggregate for sustainable construction

Abstract

Reusing demolished concrete waste is a promising alternative to natural aggregate for resource conservation and achieving sustainable environment. However, there is a need to improve their quality and performance in new concrete. Therefore, this study aims to examine the mechanical performance of normal strength concrete containing metakaolin-cement coated recycled concrete aggregate (RCA). Three mixture batches were produced at water-cement ratios (w/c) of 0.25 and 0.45. The first batch is control mix, while the second and third batches contained uncoated RCA and metakaolin-cement coated RCA (TRCA) respectively. Materials characterization and workability of fresh concrete mixes were carried out. Compressive and split tensile strengths and water absorption tendency of hardened samples were determined. Morphology of selected concrete samples was analysed with scanning electron microscopy (SEM) with energy dispersive x-ray (EDX). The experimental results were further analysed with central composite design (CCD) response surface method. Results show improvements in the physical properties of RCA aggregates and declining trends in slump values. However, relative to the control mixes, concrete mixes containing TRCA exhibited significant improvement in strength performance and low water absorption tendency compared to RCA concrete mixes. This was corroborated by the response surface models showing that both w/c ratio and TRCA amount significantly influenced the strength and water intake performance of the concrete. The study demonstrated that TRCA can be deployed as an alternative for natural coarse aggregate up to 50% substitution in making normal concrete for structural purposes.