# A Fundamental Study on an SAP Mixed Asphalt Mixture for Reducing the Urban Heat Island Effect
During midday, the temperature of an asphalt road is about 20 \({}^{\circ}\)C higher than that of grass, and the decrease in vegetation along with the increase in waterproof surfaces caused by urbanization seriously affect the UHI [12; 13]. Likewise, artificial means of transportation in the urban cities have an adverse effect. In defining the heat island phenomenon, asphalt road pavement characteristics are classified according to the porosity or amount of asphalt added, and how much they contribute to the heat island phenomenon. Many previous studies have mentioned factors such as albedo, water permeability, and water conservation on the asphalt surface layer because these factors greatly affect the surface temperature [14; 15; 16]. Therefore, it is important to alleviate the urban heat island phenomenon caused by asphalt roads. Currently, in order to lower the high asphalt temperature, local governments are water spraying roads in a manner suitable for each region. According to the spraying method, a sprinkler truck is used, and a clean road system that automatically sprinkles water at certain intervals is operated. The effect of reducing the temperature of the road surface appears significant when spraying, but the duration is not long, so the problem is that the temperature reduction effect continues only when additional spraying is carried out or increased. Recently, various studies have been conducted using an SAP (Super Absorbent Polymer) with water absorption properties as a means to effectively alleviate this urban heat island phenomenon. An SAP is a water-absorbing polymer with a network structure of polymer chains, commonly referred to as hydrophilic gels. The SAP is not soluble in water, but it absorbs it and then swells up. The SAP, in particular, can maintain absorbed water under some pressure unlike other absorbent materials such as tissue and polyurethane foam. Furthermore, the SAP has a three-dimensional network structure like a water-soluble polymer and can absorb water about 100 to 500 times its own weight without dissolving in water. The SAP types used in this study are widely used in everyday life. They are mainly used for disposable diapers, disposable items for women, and steaming packs, and recently an expanding scope means they are being used as soil repair agents and civil engineering and construction water-repellent materials [17; 18]. The application of an asphalt mixture with an SAP can delay the road pavement's temperature recovery time after water is sprayed to lower the road pavement's temperature during a heat wave. Water cooling is performed on road pavement in each region every year during heat waves, and spray trucks or clean road systems are used. The water-cooling system is an effective way to lower the surface temperature of road pavement. However, after the spraying is completed, due to evaporation and drain effects, the water quickly disappears from the surface of the road pavement and the pavement tends to return to the temperature it was before spraying. Therefore, the usage of an SAP on asphalt pavement helps delay recovery time by absorbing the water longer [19; 20; 21; 22]. In this study, an SAP was applied to asphalt mixtures to delay the temperature recovery time of road pavement, and various performance evaluations were performed. Two types of SAPs were applied to asphalt mixtures at various ratios to evaluate strength and durability. In addition, temperature change characteristics under various conditions were evaluated indoors and outdoors to evaluate the thermal characteristics of asphalt specimens applied with the SAP.