Water Permeability and Freeze–Thaw Resistance of Polyurethane-Bound Permeable Pavements under De-Icing Salt Exposure

Introduction. Permeable pavements can effectively reduce surface runoff in urban areas; however, their application in cold climates requires both rapid water infiltration and sufficient resistance to freeze–thaw deterioration exacerbated by de-icing salts. This study focuses on two key performance indicators of polyurethane (PU)-bound permeable pavement composites: water permeability and freeze–thaw resistance under de-icing salt exposure.

Methods. Four PU-bound granite aggregate mixtures were evaluated. Three mixtures consisted of both fine (0/1 mm) and coarse (2/5 mm) granite fractions with PU binder contents of 3.0%, 2.5%, and 2.0%, while the fourth mixture included only the coarse (2/5 mm) fraction with 3.0% PU binder. Water permeability was measured in both vertical and horizontal directions in accordance with LST EN 12697-19:2020. Freeze–thaw resistance was assessed after 28 cycles in a 3% NaCl solution using a CF/CDF-based testing procedure.

Results. All mixtures exceeded the required permeability threshold of 2 × 10⁻⁵ m/s. The coarse-only mixture with 3.0% PU binder exhibited the highest permeability, with vertical and horizontal coefficients of 4.37 ± 0.21 × 10⁻³ m/s and 3.87 ± 0.04 × 10⁻³ m/s, respectively. This mixture also demonstrated the lowest surface scaling after freeze–thaw exposure, with a mass loss of 0.109 kg/m² after 28 cycles. In contrast, the mixture with the lowest PU binder content showed the highest mass loss, reaching 0.513 kg/m².

Conclusions. A coarse granite aggregate skeleton bonded with 3.0% PU binder provides an optimal balance between high hydraulic conductivity and enhanced freeze–thaw resistance under de-icing salt exposure. These findings support the application of PU-bound permeable composites in paver joints and light-traffic permeable pavement systems in cold-climate urban drainage.