# Thermal Exchange and Skid Resistance of Chip Seal with Various Aggregate Types and Morphologies
## 1 Introduction  
Shortages of natural aggregate resources make the substitution of aggregates an area of interest for sustainable road engineering. Steel slag, the by-product of steelmaking, is a desirable alternative material. Initially, researchers hoped to reduce steel slag production by improving steelmaking methods, or adding steel slag to the steelmaking process again. However, these methods are costly and not effective. Therefore, the research direction of steel slag treatment has turned to how to reuse it in other fields [1; 2; 3]. At present, there are some studies on the application of slag in asphalt pavement. [PERSON] [4] evaluated the impact of steel slag on the properties of asphalt mixture, and it was found that steel slag enhanced the mechanical properties and electrical conductivity of asphalt mixtures. [PERSON] [5] verified the feasibility of recycling steel slag as an aggregate to improve the thermal conductivity of asphalt mixtures. The results show that slag has a positive effect on thermal conductivity, compared with ordinary asphalt mixtures. [PERSON] [6] reused steel slag to prepare a maintenance layer with the function of snow melting, and it was concluded that the snow melting efficiency of the mixture could be improved by steel slag. Although there are some studies on the application of steel slag in asphaltpavements, few studies have used steel slag in the preventive maintenance of asphalt pavements, especially chip seals. Skid resistance refers to the friction force during tire rotation against the pavement surface. It is a crucial parameter of the surface layer of asphalt pavement for traffic safety. Steel slag has been applied to the surface layer of roads to improve the skid resistance due to its rough texture and abundant angularity. [PERSON] et al. [7] and [PERSON] [8] found that the skid resistance of an asphalt mixture made of slag is superior to ordinary aggregates. Therefore, the skid resistance of chip seal-containing steel slag also needs to be explored. In addition, bleeding and scabbing (loss of aggregate) are major distresses of chip seals. The main reasons for bleeding are the over-usage of asphalt and hot weather, while scabbing occurs as a result of insufficient bonding between asphalt and aggregate. Several studies have concluded that the surface of steel slag is alkaline, which makes it have a stronger adhesion to acidic asphalt than ordinary aggregates [9; 10; 11]. Theoretically, the application of steel slag in chip seal can make the adhesion bond between aggregate and asphalt stronger, reduce the possibility of scabbing, and contribute to obtaining a better chip seal performance. On the other hand, it takes about 1-2 h for the hot-applied chip seal to resume use in traffic after construction since the asphalt is heated to 150-170 \({}^{\circ}\)C. Hot asphalt needs to be cooled to normal temperature before it bears the load of a vehicle. As a low-cost and fast-constructed maintenance layer, the time to resume traffic of chip seal is expected to be further reduced. Generally, steel slag has a more complicated chemical composition than ordinary aggregates [12; 13; 14], and its thermal exchange rate could be faster than ordinary aggregates. It is hoped that the thermal exchange process of chip seal will be accelerated by steel slag and that traffic can be opened earlier. The main objective of this study is to explore the characteristics of steel slag, and the effect of steel slag on the thermal exchange and aggregate retention properties of chip seal. Furthermore, the surface features, including texture depth and skid resistance, of chip seal were also evaluated. Firstly, the element and mineral composition, thermal constant and morphology of ordinary aggregates and industrial by-products were tested. Then, the thermal exchange performance and surface features of chip seal-containing steel were detected by infrared camera and laser scanning, respectively. Additionally, a sweep test was conducted on chip seal samples to evaluate their aggregate retention property.