The pavement structure tends to shrink under low temperature conditions and cracks will appear upon crossing threshold binder stiffness. Decreasing the binder viscosity at such low temperatures, by introducing additional oil fraction (aromatics and saturates) in asphalt colloidal systems, may result in improved resistance to thermal cracking. A single multi-grade engine oil (5W30) was used in this study to analyze the rheological properties imparted to binders. Rotational Viscosity (RV) test revealed that after Rolling Thin Film Oven (RTFO) aging, fresh oil and waste oil have a similar effect on decreasing the viscosity of binder and construction temperatures, reducing them by 5~8 °C. Fourier Transform Infrared Spectroscopy (FTIR) test results showed an abrupt increase of carbonyl concertation when fresh engine oil was used for rejuvenation while waste engine oil was less susceptible to oxidative aging. Dynamic analysis of modified binders proved that engine oil has better thermal cracking resistance but relaxation ability of binders and rutting resistance was impaired. Filtered waste engine oil resulted in a 35% decrement in the stiffness of binder compared to virgin asphalt after short term aging but upper Performance Grade (PG) was compromised by 1~3 °C with 2.5% oil inclusion. Unfiltered waste engine oil proved to have the least overall performance compared to fresh and filtered waste engine oil.

With the performance limitation of a conventional hot-mix asphalt mixture, the structural integrity of that is highly needed to be enhanced to increase the fatigue life of the mixture. Various geosynthetic alternatives have been widely utilized, such as geogrid, geotextile, or geomembrane layers at the bottom the mixture or on the top of a subgrade to improve the structural integrity of a hot-mix asphalt pavement system. Although reinforcing effects of such interlayers has been reported with some improvements in hot-mix asphalt pavements’ performances, such as mitigating rut or delaying reflective cracks; however, such alternatives do not enhance toughness, tensile strength, or shear strength of the hot-mix asphalt mixture itself due to that the interlayers are usually installed in between two layers in a pavement system and those interlayers do not mix with hot-mix asphalt mixtures. A new plastic fiber-reinforced hot-mix asphalt mixture was proposed in this study to provide more enhanced structural integrity of the mixture not only at the bottom of the mixture but also within the mixture. The developed mixture in this study led to significant enhancements in phenomenological toughness and fatigue life of that at least 1.5 times higher than those for conventional hot-mix asphalt mixtures as resulting from indirect cyclic fatigue tests in loading-control modes and four-point bending beam tests in displacement-control modes.

Recycled plastic fibre-reinforced hot-mix asphalt (HMA) mixtures have better fatigue resistance than plain HMA. The toughening effects of recycled plastic fibre-reinforced HMA were characterised using direct tensile loading tests. Adding a small quantity of recycled plastic fibres to HMA was found to significantly increase the mixture's fracture energy and toughness, which were calculated using the pre- and post-peak stages of tensile force–displacement curves. A theoretical model representing the pre-peak behaviour of fibre-reinforced HMA with direct tension-softening curves for various fibre contents is presented here. The enhanced toughness through post-peak analysis was also observed using toughness indices associated with fibre-bridging effect after the pre-peak composite stress. The pre-peak fracture energy model and post-peak toughness indices appeared to be governed by the direct tensile toughening of fibre-reinforced HMA's enhanced fibre-bridging effects. The pre-peak fracture energy model demonstrates the effect of fibre content on the strain energy density during the pull-out process within the pre-peak composite stress region. The maximum pre-peak fracture energy of a coarse-graded HMA mixed with recycled plastic fibres is achieved at a fibre content of 0.4% of the total weight of the HMA. The increases in the toughness indices within the post-peak composite stress region indicate that the fatigue resistance of fibre-reinforced HMA is at least 30% greater than that of control HMA.

With premature deteriorations and performance limitations of hot-mix asphalt (HMA) pavements, innovative solutions are needed to enhance fatigue life or rut-resistance of HMA. Various reinforcing methods are widely utilized such as installing geogrid, geocomposite, or geomembrane layers at the bottom HMA to improve the structural integrity of HMA pavement. Such layered systems sometime improve the field performance of HMA; however, such solutions may not enhance toughness, tensile strength, or shear strength of HMA itself due to the location of interlayer systems. A new mono-strand fiber reinforcing material for HMA is proposed in this study to effectively reinforce the HMA not only at the bottom but also inner-side. Adding a small amount of fiber into HMA leads to significant increases in the phenomenological fatigue life of fiber-reinforced HMA compared to the conventional HMA, and four-point bending beam and indirect tensile tests are performed to observe the effect of fiber reinforcement.