# Experimental Investigation into Permeable Asphalt Pavement Based on Small-Scale Accelerated Testing
## 4 Conclusions  
In this study, a piece of one-third scale accelerated loading equipment, MMLS3, was used to investigate the mechanical properties of permeable asphalt pavement under different moisture conditions of the subgrade. Three types of permeable asphalt pavement structures were designed to study the effects of surface thickness and base type on the strain responses and rutting of permeable asphalt pavement. Based on the results of this study, the following conclusions can be drawn:  
* The transverse resilient tensile strain significantly increased with increasing loading cycles with a decreasing rate, and the increase could be affected by temperature. The thickness of the surface layer and base materials had effects on the longitudinal strain, leading to different strain change patterns;
* Under dry conditions, a structure with a thinner surface layer was more prone to produce a larger permanent deformation and a lower tensile strain in the surface layer. In addition, the base materials had a significant effect on tensile strain at the bottom of the surface layer;
* Compared with dry conditions, the resilient strain of the structures with different base materials (7 PA-CTPB-D and 7 PA-CTB-D) presented a similar change trend under wet conditions. Compared with dry conditions, both the longitudinal and transverse resilient tensile strain decreased under wet conditions. In addition, compared with the rut depth under dry conditions, the average rut depth was slightly lower after 0.85 million cycles under wet conditions, which could be caused by the better compaction of the subgrade soil and the increased strength of the base materials after loading for dry conditions;
* The temperature differences at the bottom of the surface layer presented the same variation trend as the strain cycles. The temperature differences increased with increasing loading cycles during each day of loading, which indicated the strain variation was caused by both temperature and load. In addition, fully permeable asphalt pavement with a permeable base produced a higher temperature at the bottom of the surface layer, potentially leading to more damage to the surface layer. This study demonstrated the non-linear accumulation of transverse strain with loading cycles, while proposing optimized design strategies through the dual consideration of subgrade strength enhancement and hydraulic conductivity requirements. And the test conditions were closer to the field environment, which provides a reference for evaluating the long-term performance of different permeable asphalt pavement structures. Accelerated loading tests are usually loaded hundreds of thousands or even millions of times to study the long-term performance of different structures, requiring the construction of circuit roads. In this study, three different pavement structures were designed, and accelerated loading tests were carried out at the same time. The application of scaled APT with rigorous similitude principles provides a methodological advancement for an economical yet mechanistically valid pavement performance assessment. In addition, this study also pointed out the impact of temperature and load continuity on the experimental results; the temperature and the saturation degree of subgrade should be precisely controlled in future studies. Conceptualization, B.Y. and H.L. ; methodology, H.L. ; formal analysis, Y.L. ; investigation, all authors; writing--original draft preparation, B.Y. ; writing--review and editing, Y.S. ; supervision, Y.H. ; project administration and funding acquisition, H.L. and M.C. All authors have read and agreed to the published version of the manuscript. The research is supported by the National Key R&D Program of China (2023 YFE0121400 & 2023 YFB2604000), the Science and Technology Commission of Shanghai Municipality (GrantNo. 23210711400), Gansu Provincial Science and Technology Plan (23 JRRA1375), and the research project of Jiangsu Communications Holding Co., Ltd. (No. 2024 JKY13). Not applicable.