Investigation on the healing effects of microwave heating in eco-friendly pavement using e-waste

Incorporating e-waste into asphalt pavements can enhance their ability to absorb microwaves, allowing the asphalt to quickly reach its softening point under microwave exposure, flow, and fill cracks, achieving self-healing of the pavement. Depending on different heating principles, the added e-waste can be divided into two categories: microwave absorbing materials and metal shielding material. However, regardless of which material is added alone, during the microwave heating process, microwave energy will decrease along the propagation direction, leading to temperature differences in the pavement and causing uneven healing among different layers. To address this issue, this paper proposes a self-healing asphalt pavement (SHAP), where microwave absorbing materials are gradiently incorporated into the upper and middle layers of the pavement with more microwave energy, while metal reflective materials are added to the lower layer where electromagnetic energy has significantly decayed, thereby increasing the microwave absorption capacity of the pavement layer by layer. This achieves a similar warming trend across all layers after microwave heating. Based on microwave heating experiments, the effects of different added e-waste materials on the microwave heating of the pavement were studied, determining the optimal type of e-waste for each layer of the SHAP. An overall healing index (HI_average) was proposed, to maximize the HI_average, a predictive model was established using response surface methodology to determine the optimal dosage of e-waste for each layer of SHAP. Finally, a life cycle assessment demonstrated that SHAP exhibits significant economic and environmental advantages compared to conventional pavements.