Functional performance and microstructural properties of porous asphalt subjected to clogging

Abstract

Porous asphalt is designed with high air voids that increases the voids interconnectivity to improve permeability and sound absorption. However, after few years in service, these functional performances become ineffective due to clogging. Due to high air voids, debris and dust from moving vehicles and surface runoff tend to clog the voids structure. This research investigates the effect of clogging on the functional performances and microstructural of porous asphalt. Initially, a comprehensive laboratory procedure with different variables (cycles, materials, concentrations) was established to characterise the clogging potential. Then, the changes in voids properties due to internal clogging were investigated using X-ray Computed Tomography scanner and imaging technique for microstructural characterisation. Detailed image analysis procedure was developed and verified with the volumetric properties of the mix. The functional performances such as permeability, sound absorption and skid resistance of the porous asphalt were then evaluated under various clogging conditions. Based on the microstructure analysis, repeated clogging cycles have densified the top region of porous asphalt and changed the air voids structure as well as the voids interconnectivity. This has caused reduction in water permeability as more time is needed for water to permeate through the voids channel. The results also suggest clogging phenomenon reduces the sound absorbing capabilities in the porous structure particularly at high frequency due to excessive energy attenuation. For frictional performance, deposition of clogging particles on the pavement surface has changed the properties of the macro and micro-texture as indicated by the difference in British Pendulum Number (BPN) under dry and wet conditions. Overall, these results suggest that clogging phenomenon is an important factor affecting the functional performance and microstructure of porous asphalt.