# Research on Performance of a Dense Graded Ultra-Thin Wearing Course Mixture
## 1 Introduction
The result shows that maximum interlayer shear stress is negatively correlated with temperature and interlayer sliding coefficient. The cohesiveness between the thin surface layer and underlying asphalt layer is proven to be an important factor that influences the performance and durability of the thin surface layer [13]. Thus, [PERSON] [14] proposed a modified pull test method to test cohesiveness between the ultra-thin wearing layer and underlying asphalt layer. Three types of ultra-thin wearing layers (Epoxy modified bitumen, Resin and Cement) were selected. The experiment was conducted under three different temperatures (0, 10 and 20 \({}^{\circ}\)C) with a loading speed of 0.025 MPa/s. The result demonstrates the feasibility of the proposed modified test method, provided that the interface of the two layers is the weakest area. Moreover, the author also demonstrated that the Epoxy modified bitumen-based surface layer has better cohesiveness than the other two types of layers. Pavement performance decreases over time, and thus needs to be rehabilitated once the existing pavement is unable to satisfy the traffic demand. Several researchers also focused on ultra-thin wearing layer recycling since high quality materials are used in the ultra-thin wearing layer. Both environment protection and cost reduction could be achieved by recycling high-quality used materials. [PERSON] et al. [15] conducted research to investigate if the reclaimed ultra-thin wearing layer material could be used in the chip seal or Superpave mixtures. Sweep test based on the American Society for Testing and Materials (ASTM) D7000-04 was conducted to observe the chip retention of ultra-thin wearing layer millings. Different percentages (0%, 10%, and 20%) of ultra-thin wearing layer millings were added to the Superpave mixture. Rutting, stripping and moisture sensitivity tests were conducted to evaluate the performance of the Superpave mixture. The sweep test indicates that reclaimed ultra-thin wearing layer millings do not contribute to chip retention. However, an ultra-thin wearing layer milling addition was proven to have a positive effect on the performance of Superpave mixture. The ultra-thin paving technique has been extensively used in China [16], since its first adoption in the 1990s [17]. However, several drawbacks of the ultra-thin paving technique occurred in engineering practices such as low degree of compaction, moisture damage and rapid attenuation of sliding resistance at a later stage. As to open-graded ultra-thin paving material, the situation could be even worse. Because of the high void ratio of open-graded ultra-thin paving material, water could easily permeate into the pavement structure. It would lower the bonding strength between pavement layers, causing raveling and reducing the durability of ultra-thin paving materials. In view of the existing problems of the current ultra-thin technique, a dense-graded ultra-thin wearing mixture was designed and then further modified by a multi-chain polyolefin modifier to get the modified ultra-thin wearing mixture in this study. Both laboratory and field tests were conducted to fully evaluate the road performances, wearing resistance and bonding conditions with sub-layers of the modified ultra-thin wearing mixture.