Balancing Mechanical Strength and Hydraulic Functionality of Fine Aggregate Free Pervious Concrete Using Expanded Vermiculite

Pervious concrete is widely used for sustainable pavement applications due to its ability to reduce surface runoff and enhance groundwater recharge; however, its application is often limited by low mechanical strength caused by the absence of fine aggregates. This study focuses on identifying an optimal balance between mechanical strength and hydraulic functionality of fine aggregate free pervious concrete through the incorporation of expanded vermiculite (EV) as a lightweight aggregate substitute. EV was introduced at 0%, 5%, 10%, and 15% as a partial replacement of the fine aggregate fraction typically present in conventional concrete. Specimens were designed using a modified volumetric approach based on ACI 522R-10. Compressive strength was evaluated at 7 and 28 days, while porosity and permeability were assessed at 28 days. The results show that increasing EV content significantly enhances compressive strength, reaching 17.08 MPa at 15% EV due to internal curing and pore densification. However, excessive EV incorporation leads to a sharp reduction in porosity and permeability, indicating a loss of hydraulic functionality. A balanced performance was achieved at 5% EV, where meaningful strength improvement was obtained while maintaining effective infiltration capacity. These findings highlight the importance of dosage control when designing fine aggregate free pervious concrete systems for infiltration dependent applications.