Experimental investigation of ecological semi-flexible pavement with silica sand as a partial substitution of cement

The exploitation of locally available and abundant natural resources such as silica sand and its use as a supplementary cementitious material in the production of grout used in semi-flexible pavement (SFP) surfaces is of paramount importance in reducing transportation costs and emissions, contributing to more sustainable development practices, and reducing the overall environmental impact of cement plants. SFP or injected pavement, is a porous asphalt structure with 25–35% voids, filled with cementitious grout. SFP is distinguished by its robustness, resistance to deformation, and exceptional longevity, enabling it to endure substantial traffic loads and extreme weather conditions, hence offering a strong and dependable road surface that is comparatively simpler to maintain than other road construction types. This study focuses on developing a novel sustainable cementitious grout for SFP by partially substituting traditional cement with quartz silica sand powder (QSP) in different proportions (10%, 20%, and 30%). The grout mixtures were evaluated for flow and mechanical properties. Also, SFP samples were made by adding a 5% SBS modifier to a hot mix porous asphalt (HMPA) and then filling the holes with a predesigned cement-based grout then these samples were assessed for Marshall stability and moisture damage resistance tests. The results demonstrated that replacing cement with more than 10% of QSP reduces compressive strength and stability. This is due to the reduction in workability caused by water absorption in the grout mixture. This, in turn, increases the water-to-cement ratio to achieve the required fluidity, as well as increasing the porosity and decreasing the volume of hydration products. Therefore, this study suggests that 10% of QSP is the optimum replacement ratio as it achieves the required fluidity and increases the compressive strength, stability, and tensile strength ratio by 20.7%, 13.4%, and 12.0% respectively at 28 days of curing compared to the reference grout mixture. This mixture is considered suitable as it combines the properties of durability and environmental objectives by reducing the grinding energy and its use in severe conditions.