Enhancing desert sand concrete with fibre-reinforced polymer (FRP) confinement: mechanical and microstructural perspectives

River sand is a key natural resource in the construction industry, primarily used in concrete production. However, its overuse has led to significant ecological and environmental imbalances worldwide. This study investigates the potential of Australian desert sand as a partial replacement for river sand in concrete production and evaluates the performance of specimens confined with fibre-reinforced polymer (FRP) using a multi-scale experimental approach. Replacing 50 % of river sand with desert sand led to a slight reduction in compressive strength but improved tensile properties, which were attributed to a denser concrete matrix and reduced porosity. Microstructural analyses, including scanning electron microscopy (SEM) and micro-XCT, revealed significant decreases in pore size and volume for desert sand concrete (DSC), thereby enhancing the material compactness. FRP confinement provided a slightly greater strength enhancement for desert sand concrete (DSC) compared to normal concrete (NC), although strain enhancement was lower for DSC due to differences in the internal microstructure. Furthermore, existing FRP confinement models developed for NC demonstrated adequate accuracy in predicting the stress-strain behaviour of FRP-confined DSC, indicating no need for a new stress-strain model. These findings highlight the potential of desert sand as a sustainable alternative for concrete production.