Microwave healing and deicing of asphalt pavements containing industrial slags: Towards intelligent and sustainable road winter maintenance

Due to the unique geographical and climatic conditions of the Nordic regions, roads are particularly vulnerable to low-temperature damage, resulting in early pavement cracking and ice formation. Microwave heating (MH), an advanced and sustainable winter maintenance technique, can enhance the self-healing behavior and deicing efficiency of asphalt pavements. Additionally, substituting road aggregates with certain waste slags that exhibit superior strength and wave-absorbing properties can improve MH sensitivity while reducing the reliance on natural aggregates. Against this backdrop, this thesis focuses on enhancing the self-healing and deicing efficiency of asphalt pavements using MH technology. The healing efficiency of asphalt pavements is evaluated through cyclic cracking-healing-cracking tests under varying conditions, including heating time, power, and cycle. The static magnetic and electromagnetic properties of different waste slags are analysed to identify the optimal wave-absorbing slag. Microwave deicing performance, carbon emissions, and cost-benefit analyses are conducted on asphalt pavements containing varying amounts of slags under different freezing temperatures and ice thicknesses. A thermal camera is employed to monitor surface temperature changes, shedding light on the temperature transfer mechanism during the healing and deicing processes. Furthermore, the binders are extracted to compare their properties and assess the damage caused by freeze-thaw (FT) cycles and MH. The findings reveal that appropriate heating time and power significantly enhance the effective healing area, achieving a healing efficiency exceeding 80%. However, healed samples remain susceptible to re-cracking. The microwave-absorbing properties of waste slags are influenced by heating frequency, with steel slag demonstrating superior static magnetic and microwave absorption performance at 2.45 GHz (the frequency used in this study), making it a recommended material for pavement design. The deicing efficiency is affected by the moisture generated by melting ice, leading to discrepancies between ideal and actual ice-melting time. Moreover, while incorporating steel slag can result in uneven heating, reducing deicing efficiency at higher slag contents, steel slag asphalt pavement still achieves significantly higher microwave deicing efficiency compared to conventional pavements. Additionally, steel slag asphalt pavements produce comparable carbon emissions but offer substantial economic cost benefits. Lastly, FT cycles accelerate aging in neat binders, negatively impacting their performance, while polymer-modified binders exhibit more stable performance, making them more suitable for MH applications. This thesis proposes a self-healing and deicing asphalt mixture design that considers multiple environmental factors and provides practical solutions for waste slag utilization. The research findings contribute to improved road maintenance efficiency, reduced dependence on nonrenewable resources, and significant environmental and economic benefits.