# A Fundamental Study on an SAP Mixed Asphalt Mixture for Reducing the Urban Heat Island Effect
## 3 Results and Discussion
### Thermal Properties Results
#### 3.2.2 Results of Outdoor SAP Asphalt Thermal Properties  
Based on the results of the indoor experiment, an outdoor experiment was conducted to verify the performance of the SAP asphalt mixtures under external environmental conditions. Samples were prepared and evaluated according to the type and content of the SAP, and the average air temperature during the test was 26.3 \({}^{\circ}\)C. The specimens were sprayed for 1 min (400 mL) using an automatic sprayer (Keyyang Industry, HY-76, Chungju, Republic of Korea), and then the temperature change in the specimens was photographed over time using a thermal imaging camera (BOSCH, GTC400C, Stuttgart, Germany). During this test only the Non-SAP and 5% SAP contents from both types were  
Figure 14: Surface temperature variation in SAP-500 asphalt specimen.  
Figure 15: Surface temperature variation in SAP-3500 asphalt specimen.  
produced and experimented on because the 3% and 7% SAP contents were less efficient and durable. Figure 16 shows images of specimens before spraying, and the Figure 17 images were taken immediately after spraying. The Figure 18 images were taken 1 h after spraying and the Figure 19 images were taken 2 h after spraying, and analysis was conducted based on the temperature distribution bar. Before spraying, all specimens had a similar temperature distribution, and the maximum temperature was measured to be about 52.2 \({}^{\circ}\)C.  
After 1 min of spraying, the surface temperature of the Non-SAP specimen was measured to be approximately 3 \({}^{\circ}\)C higher than the other specimens, whereas the surface temperature of the SAP specimen was measured to be lower over the entire pavement surface. This means that in the case of Non-SAP asphalt, the air void was small, so the amount of water exceeding the surface air void after spraying flowed to the side or was collected, and also evaporation begun at the same time as spraying causing the Non-SAP specimen to quickly recover to its original temperature. However, in the case of the SAP asphalt, the temperature recovery was delayed because the SAP absorbed water flowing inside the pavement quickly and it slowly evaporated. When comparing between SAP-500 and SAP-3500, the SAP-500 surface temperature distribution tended to be slightly lower. This is because SAP-3500 is finer than SAP-500, which made it more widely distributed than SAP-500 and hence it had a better temperature distribution even though the same amount of water was sprayed for 1 min for both specimens.  
Figure 16: Temperature distribution before spraying (from left: Non-SAP; SAP-500 5%; SAP-3500 5%).  
Figure 17: Temperature distribution immediately after spraying (from left: Non-SAP; SAP-500 5%; SAP-3500 5%).  
After 1 h of spraying, the temperature distribution was lower in the SAP asphalt than in the Non-SAP asphalt. There were areas where the SAP-500 asphalt differed from the Non-SAP asphalt by a range from at least 3 \({}^{\circ}\)C to a maximum of 9 \({}^{\circ}\)C, and SAP-3500 differed from the Non-SAP asphalt by a range from at least 2 \({}^{\circ}\)C to a maximum of 10 \({}^{\circ}\)C. Compared to the Non-SAP asphalt, the temperature distribution gap of the SAP asphalt was severe in the marked area, which is considered to contain a large amount of moisture as it was a SAP-intensive area at the time of mixing.  
After 2 h of spraying, the temperature distribution was higher in the Non-SAP asphalt than other specimens, and there was a difference of about 3 to 5 \({}^{\circ}\)C in the SAP-500 asphalt and 2 to 5 \({}^{\circ}\)C in the SAP-3500 asphalt. In the indoor experiment, the original temperature was restored in about 40 min, but the outdoor experiment maintained a low temperature for a long time. Unlike the indoor experiment conducted at the highest temperature, the maximum temperature of the asphalt surface outdoors was about 52 \({}^{\circ}\)C. Additionally, the influence of wind, humidity, and sprinkling amount was believed to be the reason the cooling effect was maintained for a longer time.