This study assessed the water stability of asphalt mixtures incorporating granite aggregates. A silane coupling agent was adopted to modify the surface of the granite aggregates, and scanning electron microscopy, contact angle measurements, Fourier transform infrared spectroscopy, and X-ray fluorescence were used to analyze the micro- and meso-characteristics of the aggregates. Effects of the silane treatment on the water stability of the mixtures were further evaluated by immersion and vacuum saturation Marshall tests and freeze–thaw splitting tests. The results indicated that the silane coupling agent had grafted onto the aggregate surface via chemical interactions, resulting in obviously raised contact angles and greatly reduced hydrophilicity. Additionally, the deposited organic film also reacted with the asphalt and formed a tighter bonding interface between the asphalt and aggregates, resulting in an asphalt mixture with a higher residual stability and splitting tension strength ratio when under environmental stress.

An ultrathin wearing course (UTWC) is a preventive maintenance treatment method for a road surface which can improve the safety and comfort of driving by providing superior skid resistance. However, the skid resistance is a concern after multiple years of loading cycles. The role of coarse aggregate in preventing the skid resistance deterioration of an UTWC is not fully understood. This study determined the effect of coarse aggregate types and nominal maximum aggregate size (NMAS) on the skid resistance deterioration of an UTWC. Different types of stone mastic asphalt (SMA), which are used in three kinds of coarse aggregates (diabase, limestone, and basalt) and three kinds of NMAS coarse aggregate (SMA-5, SMA-8, and SMA-10), were prepared for the test. A Model Mobile Load Simulator 3 (MMLS3) was used to simulate repeated vehicle loading and abrasion. After specific loading cycles, the skid resistance of an UTWC was measured by the British pendulum number (BPN) test and the sand patch test. The BPN and mean texture depth (MTD) were chosen to evaluate the skid resistance of the UTWC. The results showed that the BPN value of an UTWC is sensitive to the type of coarse aggregate. The skid resistance of SMA-8 with diabase and basalt is better than the performance of SMA-8 with limestone. The results of grey relational analysis (GRA) showed that the loss polishing stone value (LPSV) index should be used to evaluate the coarse aggregate of the UTWC. The MTD value of an UTWC is sensitive to the NMAS. The skid resistance of SMA-8 and SMA-10 is better than that of SMA-5. The skid resistance deterioration (BPN and MTD) of UTWC was fitted by an exponential model. The measured data of the Guangxi Nanyou expressway for 5 years showed that the exponential fitting equation can describe the attenuation process of the skid resistance of an UTWC in actual engineering. The findings will play an essential role in selecting coarse aggregates in an UTWC.

Composite modification technology is widely used in the materials field. To enhance the property of polyurethane modified asphalt and realize its application in road engineering, the bone glue/polyurethane composite modified asphalt (CMA) was prepared using bone glue, polyurethane, and neat asphalt in this research. The bone glue content ranges 5–10%, that of the polyurethane is 1–5%. The relationship between the modifier’s content and the conventional properties and rheological properties of CMA was revealed by response surface methodology (RSM). The CMA performance was further verified under the optimal content of the bone glue and polyurethane. The differences of properties of styrene–butadienestyrene (SBS) modified asphalt mixture, neat asphalt mixture, and bone glue/polyurethane CMA mixture were compared and analyzed by using the pavement performance test. The results showed that the CMA’s conventional properties and rheological properties are improved. The optimal bone glue content and polyurethane content determined by RSM are 6.848% and 2.759%, respectively. The low-temperature crack resistance and water stability of the CMA mixture are enhanced, better than neat asphalt mixture and SBS modified asphalt mixture. The CMA mixture’s dynamic stability is 85% of SBS modified asphalt mixture, but it is 2.4 times of neat asphalt mixture. The result indicated that the bone glue/polyurethane CMA mixture still has certain advantages of high-temperature stability. In this research, the composite modification of bone glue and polyurethane can significantly enhance the characteristic of asphalt and asphalt mixture and provide a new method for applying and promoting polyurethane modified asphalt in road engineering.

In order to study the influence of freeze-thaw cycles on the multi-axial strength of AC (Asphalt Concrete)-13 and SMA (Stone Mastic Asphalt)-13 asphalt mixtures which are widely used in China, triaxial tests were carried out in the laboratory. Two nonlinear failure criterions under three-dimensional stress states in octahedral space were established. A linear model for engineering design and its simplified testing method were then presented. The three-dimensional failure criteria of asphalt mixtures after 0, 1, 3, 5, 10, 15, 20 freeze-thaw cycles were also proposed. The results indicated that the multi-axial strength decayed significantly after 20 freeze-thaw cycles. It is noteworthy that the strength degrades rapidly during the first 5 freeze-thaw cycles. Compared with AC-13 asphalt mixture, the SMA-13 asphalt mixture exhibits better performance on the resistance to freeze-thaw damage, and it is recommended as the upper surface layer material of pavement structure.