Radiative cooling for thermal management of ballastless track slab in high-speed railways

With the rapid development of modern high-speed railways and the increasing frequency of extreme high-temperature weather, the impact of thermal issues such as cracking and upper arch gaps in ballastless track slabs has become increasingly prominent. However, current thermal management techniques for ballastless track slabs are limited, with cooling tubes and coatings being the primary methods. Cooling tube systems, which through fluid-filled pipes within the track slabs to dissipate heat, can be effective but pose challenges due to their high energy consumption, complex installation, and maintenance requirements. As an environmentally friendly and energy-efficient passive cooling method,the application effect of radiative cooling coating on building roofs and external walls, as well as photovoltaic modules has been proved, is anticipated to enhance the thermal conditions of ballastless track slabs and mitigate thermal problems. This article first reviews the principles of radiative cooling technology, then summarizes relevant studies on common radiative cooling materials and cooling structure designs. Common materials include selective emission materials (SiO2 and some metal oxides), reflective materials (TiO2 and BaSO4), and matrix materials (resins, polymers). Typical cooling structure designs include multilayer and metasurface structures. At last, this review summarized current research on the application of radiative cooling coatings in ballastless track slabs. The research shows that coatings can reduce track slabs surface temperatures by approximately 10 °C, significantly lowering internal thermal stress and preventing the formation of cracks and gaps. It can be seen that radiative cooling has the potential to make a substantial contribution to the thermal management of ballastless track slabs. Future improvements in the durability of these coatings on ballastless track slabs and reductions in application costs will be essential for large-scale implementation. This review aims to provide a reference for the application and development of radiative cooling technology in the thermal management of ballastless track slabs, promoting the safe and reliable operation of high-speed railways.