Performance of pervious concrete prepared using alkali-activated slag and recycled concrete aggregates

This study developed an eco-friendly pervious concrete (PC) using alkali-activated slag (AAS) as the sole binder and 100% recycled concrete aggregates (RCA). A novel target porosity-based volumetric design method was proposed and validated, enabling precise control over pore structure across a wide porosity range. The permeability coefficient increased linearly with porosity, but the hydraulic efficiency (slope α) decreased from 10.7 to 3.2 as RCA size increased from 5–10 mm to 16–20 mm, indicating that pore architecture—not just total porosity—governs water transport. Freeze-thaw deterioration was initiated by physical damage from water freezing in interconnected macro-pores, causing significant mass and strength loss in high-porosity specimens. Microstructural analysis confirmed the excellent chemical stability of the AAS binder under freeze-thaw conditions, with no decomposition of C-A-S-H gel. Notably, the volume of "harmless" gel pores (<10 nm) increased after freeze-thaw cycling, suggesting the AAS matrix dissipates stresses through nano-scale pore reorganization rather than micro-crack propagation. This work supports the application of eco-friendly PC in sponge city infrastructure.