Steel slag has been commonly used in road engineering as cementitious material; however, its application in base course is not widely reported. Four contents of steel slag (0%, 30%, 50%, 75% by volume) were blended into different cement (3%, 4%, 5%, 6% by weight)-treated aggregates. Mechanical properties, volume stability, economic benefits and environmental influences of steel slag mixtures were investigated for the feasibility of applying steel slag in semi-rigid base course. Abrasion, crushing and elongated particle content were compared against limestone aggregate, showing that steel slag has the potential of replacing natural aggregate in concrete. Steel slag is beneficial for reinforcement of the strength and stiffness. The mixture has the highest strength and stiffness when bended with 50% steel slag at 4% cement content. By treating steel slag with CH₃COOH or adding silica fume, volume expansion of steel slag can effectively be controlled. Larger size steel slag (>4.75 mm) and higher cement content are recommended due to heavy metal leaching risk, especially in salty humid areas. Steel slag has sound economic benefits due to the relatively low price. Environmental benefits can also be achieved given that the transport CO_2eq emission of steel slag is accounted for. With proper control in production process, steel slag is a very promising alternative material to be utilized in cement-stabilized base course in road engineering.

Asphalt pavements at high altitudes are susceptible to aging and disease under prolonged action of UV light. To improve their anti-ultraviolet aging performance, UV-531/SBS-modified asphalts with UV-531 dopings of 0.4%, 0.7%, and 1.0% were prepared by the high-speed shear method, and the effect of UV-531 on the conventional performance of SBS-modified asphalt before aging was studied by needle penetration, softening point and 5 °C ductility tests. The high- and low-temperature rheological properties of UV-531/SBS-modified asphalt before and after aging were also analyzed by high temperature dynamic shear rheology test and low-temperature glass transition temperature test. Finally, the effect of UV-531 on the anti-aging performance of SBS-modified asphalt was evaluated by three methods, including rutting factor ratio, viscosity aging index, and infrared spectroscopy. The results show that with the increase of UV-531 doping, the needle penetration and 5 °C ductility show an increasing trend, but the effect on the softening point is small. The high temperature stability of SBS-modified asphalt is not much affected by the addition of UV-531, and the low-temperature stability is improved, and when 0.7% UV absorber is added, SBS-modified asphalt shows better low-temperature performance. The results of all three evaluation methods show that the addition of UV-531 significantly improved the anti-UV aging performance of SBS-modified asphalt, with the amount of 0.7% providing the asphalt with the best anti-UV aging performance. The results of the study can provide an important reference for improving the anti-ultraviolet aging performance of SBS-modified asphalt.

Recycling waste rubber is essential for promoting circular economy practices, reducing environmental pollution, and conserving resources. This study examines the performance of crumb rubber-modified asphalt mixtures incorporating two light oils (aromatic oil and tall oil) to alleviate the high viscosity and poor workability of asphalt with high rubber content. Mixtures were prepared using a neat asphalt modified with 20% crumb rubber and 5% light oil (by mass of the neat asphalt), combined with basalt aggregate in an AC-13 gradation. High-temperature performance was evaluated via Marshall stability and wheel tracking tests at 60 °C, moisture sensitivity through immersion Marshall and freeze–thaw splitting tests, and low-temperature cracking resistance using semi-circular bending (SCB) tests at 15 °C. Tensile strength and fatigue life were measured by splitting tests at 25 °C and fatigue tests at 15 °C, respectively. Results indicate that the rubber-modified mixtures showed significant improvements: the total deformation decreased by 44.7% and 64.1% for aromatic oil- and tall oil-modified mixtures, respectively, compared to the neat asphalt. Fracture toughness increased by 46.5% and 71.9%, and tensile strength improved by 40.2% and 63.6%, respectively. At a low stress ratio (0.281), mixtures with tall oil exhibited a 47.9% longer fatigue life than those with aromatic oil. Tall oil demonstrated superior performance, attributed to enhanced rubber swelling and crosslinked network formation, which improved viscosity and aggregate coating. The findings confirm that light oil-modified rubber asphalt mixtures, especially those containing tall oil, present a viable approach for developing high-performance and environmentally sustainable road pavements.