# A Fundamental Study on an SAP Mixed Asphalt Mixture for Reducing the Urban Heat Island Effect
## 4 Conclusions  
This study was conducted to evaluate the reduction effect of the urban heat island phenomenon of asphalt pavement applied with an SAP. The durability and temperature reduction performance of asphalt mixtures applied with various types and contents of SAPs were studied, and the conclusions are as follows:  
Figure 19: Temperature distribution 2 h after spraying (from left: Non-SAP; SAP-500 5%; SAP-3500 5%).  
Figure 18: Temperature distribution 1 h after spraying (from left: Non-SAP; SAP-500 5%; SAP-3500 5%).  
* Based pm the results of the performance of the asphalt mixture mixed with an SAP, when the SAP content was less than 7% the mixture design criteria of the mixture were satisfied. In the case of indirect tensile strength, the Marshall stability and crack resistance of the Non-SAP asphalt mixture had better results than the asphalt mixtures with SAP. However, the dynamic stability results showed that the rutting resistance increased by more than three times for asphalt mixtures with the SAP compared to the Non-SAP asphalt mixture.
* As a result of the indoor experiment on the thermal characteristics of the SAP asphalt, it was confirmed that the effect of delaying the temperature recovery was improving as the content of the SAP increased. Compared to the Non-SAP asphalt, the surface temperature immediately after spraying decreased by 10 \({}^{\circ}\)C, and the temperature recovery was delayed by 5 to 30 min depending on the SAP content.
* In the case of a high content of the SAP (7% or higher), the surface temperature lowered after spraying was maintained or tended to rise after lowering. This thermal behavior is generally the same as the temperature change behavior of the porous asphalt surface, which has the effect of improving the temperature recovery delay effect similar to that of the SAP asphalt mixture with a high content of 7% or more.
* The SAP asphalt indoor and outdoor experiments showed that the delay effect became better as the SAP content increased when a sufficient amount of spray was applied. The recovery temperature was delayed for more than 1 h after the surface temperature decreased by about 10 \({}^{\circ}\)C, and there was a clear difference in the Non-SAP.
* Although an SAP of 7% or higher exhibits thermal behavior characteristics similar to porous asphalt, the most important thing is to establish an SAP optimal content and required porosity that can exhibit temperature recovery delay effects while ensuring the porosity of asphalt. There is a space for absorbing the expansion stress of the SAP. It is concluded that further research on porosity and thermal behavior is needed by applying the SAP to porous asphalt.  
Conceptualization, D.-S.J. and C.B.; methodology, D.-S.J., C.-S.L. and K.L.; investigation, K.L. and C.B.; writing--original draft preparation, D.-S.J. and C.-S.L.; writing--review and editing, C.B. All authors have read and agreed to the published version of the manuscript.  
This research was supported by the Korea Agency for Infrastructure Technology Advancement (KAIA), and funded by the Ministry of Land, Infrastructure, and Transport (grant number RS-2023-00243421).  
Not applicable.  
The original contributions presented in the study are included in the article, and further inquiries can be directed to the corresponding author.  
The authors declare no conflicts of interest.