Combining microwave healing and permeability testing in porous asphalt mixtures for blue-green infrastructure pavements

Porous Asphalt Mixtures (PAMs) are widely used in permeable pavement systems for Blue–Green Infrastructure (BGI) applications to manage and treat surface runoff in urban and transport infrastructures. However, their hydrological and structural performance can be compromised by compaction-induced anisotropy and cracking. In this context, the valorisation of industrial by-products and the implementation of heating-based self-healing technologies can improve the performance of the PAMs. This study investigates the combined effects of Blast Furnace Dust (BFD) and microwave heating on crack-healing and vertical permeability in Superpave-compacted PAM for BGI applications. Asphalt mixtures containing 0%, 4%, and 8% BFD (i.e., as a fine-aggregate replacement) were characterised in terms of bulk air-void content, surface-connected voids via 3D scanning, and vertical permeability measured using a falling-head permeameter. The novelty of this study lies in inducing crack damage under controlled low-temperature fracture conditions, subjecting specimens to repeated microwave heating cycles within the bitumen softening range, and measuring permeability before and after cracking, as well as following healing. The main results indicate that BFD modifies the conductive pore network, reducing permeability and decreasing face-to-face anisotropy. Microwave heating promotes mechanical recovery, with hydraulic changes governed primarily by pore-network conductance rather than bulk void content alone. Overall, the PAMs containing 4% BFD exhibited the most balanced multifunctional performance, combining stable healing, lower energy demand, reduced permeability anisotropy, and more predictable vertical drainage behaviour, making it the recommended design for BGI applications.