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Highlights • Seven additives were classified into three grades based on the Hamburg wheel tracking device (HWTD) testing results. • An optimal content exists for most additives in achieving the best HWTD testing performance. • J nr 3.2 did not underestimate the rutting resistance of polymer modified asphalt as G*/sin δ did. • J nr 3.2 was more reliable than G*/sin δ in characterizing the rutting potential of asphalt mixtures. Abstract Asphalt modification technology is diversifying and developing complexity to overcome early permanent deformation and ensure satisfactory performance for asphalt concrete pavements. The Hamburg Wheel Tracking Device (HWTD) test has been reported to be successful in assessing asphalt mixtures' rutting performance. This study includes a comprehensive investigation of the effects of different additives at various contents upon the HWTD testing results of asphalt mixtures. According to the degree of their improvement of the rutting performance in the HWTD test, additives were classified into three categories: (1) the first grade including linear styrene–butadiene–styrene (SBS), branched SBS and Gilsonite; (2) the second grade including high-density polyethylene, and polyphosphoric acid; and (3) the third grade including crumb rubber. Additionally, it was found that higher dosages of modifiers do not necessarily result in the improvement of Hamburg performance, and an optimal content exists for most additives. After the extensive mix testing, the dynamic shear rheometer (DSR) testing results were correlated to the HWTD test results in two categories: polymer modified asphalt and non-polymer modified asphalt. It was found that the compliance value J nr 3.2 from the Multiple Stress Creep Recovery (MSCR) test did not underestimate the rutting resistance of polymer modified asphalt compared to non-polymer modified asphalt as the current rutting factor G*/sin δ did. J nr 3.2 was more reliable than G*/sin δ in characterizing the anti-rutting performance of asphalt mixtures no matter they were polymer modified or non-polymer modified. However, different criteria for J nr 3.2 should be adopted for the polymer modified asphalt and non-polymer modified asphalt respectively. [ABSTRACT FROM AUTHOR]

• OGFC-5 mixtures with different gradations and asphalt contents were investigated. • Cantabro test was used to evaluate moisture susceptibility of OGFC-5 mixtures. • The IDEAL-CT test was used to evaluate the cracking resistance of OGFC-5 mixtures. • Pearson correlations between durability, and air voids as well as asphalt film thickness were analysed. The ultra-thin friction course is one of the most effective treatments in highway preventive maintenances, but insufficient durability of mixtures seriously restricts the service life of ultra-thin friction course. This paper investigated the durability of Open-Graded Friction Course (OGFC)-5 ultra-thin friction course mixtures with different gradations and asphalt contents. Performances of raveling resistance, moisture susceptibility, rutting resistance, stripping resistance, and fracture resistance were evaluated by Cantabro test, Hamburg wheel tracking (HWT) test, and Indirect Tensile Asphalt Cracking Test (IDEAL-CT), respectively. The Pearson's correlation analysis between durability indicators and air voids as well as asphalt film thickness were also conducted. The results showed that mixtures with denser gradation exhibited better raveling resistance and relatively enhanced moisture susceptibility. However, the denser gradation would decrease the rutting resistance and stripping resistance of mixtures, as well as increase the fracture propagation rate, thus a reduced fracture resistance performance. Increasing asphalt content could improve the performance of resistance to raveling, moisture damage, stripping, and fracture. Higher asphalt content also enhanced the rutting resistance of mixtures while the asphalt content was not recommended to be extremely high. Results of Pearson correlation analysis showed that the smaller air voids and asphalt film thickness could result a better raveling resistance and moisture susceptibility performance of OGFC-5 mixtures. However, for the performance of resistance to rutting, stripping and fracture, the larger air voids and asphalt film thickness were required. Therefore, during the design process of OGFC-5 ultra-thin friction course mixtures, the air voids and asphalt film thickness should be determined in combination with the concerned performance. [ABSTRACT FROM AUTHOR]

• Gilsonite improves the cohesive/adhesive strength and surface energy of asphalt. • High-density polyethylene and crumb rubber enhance the asphalt healing property. • Surface energy test reveals the mechanism of asphalt mechanical property variation. • The evaluation accuracy of binder bond strength test is verified. Asphalt modifications can contribute to the moisture susceptibility and fatigue resistance of asphalt mixtures. This study investigated the effects of various asphalt modifications on the bond and healing properties of modified asphalt binders and the mechanism of changes caused by the modification. Five modified asphalt binders were prepared in the laboratory for this study, including SBS-modified asphalt, crumb rubber-modified asphalt, terminal blend (TB) rubberized asphalt, high-density polyethylene (HDPE)-modified asphalt, and gilsonite-modified asphalt. A modified binder bond strength (BBS) test was applied to evaluate the bond and healing performance of five modified binders at both dry and wet conditions. The surface free energy (SFE) test was conducted on the modified binders to investigate the cohesion/adhesion energy variation due to the binder modification. In addition, the ravelling resistance, moisture susceptibility, and fatigue life of the asphalt mixtures prepared using the modified binders and basalt (which is widely used in China) were measured using the Cantabro test, Hamburg wheel-tracking test, and four-point beam fatigue test, respectively. The performance results of the asphalt mixtures are employed to verify the findings of BBS and SFE tests for the modified binders. It is found that the modified BBS test provides a promising tool for evaluating the bond and healing properties of modified asphalt binders, and the SFE could help to explain the mechanism of binder modification. The testing results indicate that gilsonite enhanced the bond strength and surface energy of asphalt, and high-density polyethylene significantly improve the healing performance. [ABSTRACT FROM AUTHOR]

• Asphalts of different SBS contents (4.5%, 6.0%,7.5% and 9.0%) were investigated. • The increase of SBS content makes the asphalts and mixtures more elastic. • The rutting performance of mixtures was evaluated by HWT test at 50 °C, 60 °C and 70 °C. • The effect of SBS content increase on the performance enhancement progressively decreases. Open-graded friction course (OGFC) pavement has the benefits of removing pavement surface water, absorbing traffic noise, increasing friction resistance, etc. However, the insufficient durability restricts the service life of OGFC pavement. To settle this problem, the high content styrene-butadienestyrene (SBS) polymer modified asphalt was selected as binders in the OGFC mixture. This paper prepared four SBS modified asphalts with contents of 4.5%, 6.0%, 7.5%, and 9.0%, respectively. The Brookfield viscosity test and frequency sweep test were carried out to evaluate the rheological properties of asphalt. And the Cantabro test, indirect tensile strength ratio (TSR) test, Hamburg wheel tracking (HWT) test, and four-points beam bending (4PB) test were conducted respectively, to evaluate the raveling resistance, moisture susceptibility, rutting resistance and fatigue cracking resistance of OGFC mixture. The results showed that the addition of SBS content made the asphalt more elastic thus decreasing the sensitivity of viscosity to temperature, increasing the complex modulus as well as decreasing the phase angle. Meanwhile, the increasing SBS content also elevated the indirect tensile strength and the initial stiffness modulus and decreased the phase angle of the OGFC mixture. With the increase of SBS content, the raveling resistance, moisture susceptibility, fatigue cracking resistance and rutting resistance of OGFC mixture were entirely improved and the enhancement effect on rutting resistance at elevated temperature was more obvious. For high SBS content polymer modified asphalt, the effect of SBS content increase on the performance enhancement of the OGFC mixture progressively decreased and the SBS content of 7.5% was recommended to utilize in OGFC pavement construction. [ABSTRACT FROM AUTHOR]