Development and performance evaluation of high performing hybrid hot mix asphalt

Long-term performance and sustainability of asphalt pavements could be achieved by developing hot mix asphalt (HMA) composite that possesses enhanced resilience, toughness, ductility, and durability under repeated traffic loading and extreme weather conditions. Such composite could improve the design life of pavement infrastructure and save taxpayers dollar spent. Literature research reveals that rubber and fibers alone have distinct characteristics, which upon incorporation into HMA improves its mechanical characteristics. Rubber particles can effectively dissipate the energy while maintaining their shape and behave as hyper elastic inclusion thus hindering the propagation of cracks until a high amount of energy is rendered to the crack front. Also, rubber improves the viscosity and aids in transitioning from softer to stiffer binder, which is more resistant to plastic deformation. Alternatively, the addition of fibers in HMA makes the asphalt matrix stiffer. Fibers provide interlocking of aggregates due to their intricate spatial enmeshment that helps in resisting post-peak stresses after crack initiation. Such kind of reinforcement is effective in hindering the crack growth due to the crack bridging mechanism and wider stress-strain distribution along with increasing the binder viscosity. This study investigated the rutting, fracture and reflective cracking characteristics of a composite HMA utilizing crumb rubber and polyvinyl alcohol fiber (PVA). Superpave mixture design method was adopted to develop control HMA, CRM modified, PVA reinforced as well as CRM-PVA HMA. Resistance to moisture induced sensitivity was assessed to evaluate stripping potential of control and modified HMA. Similarly, SCB fracture test was employed to evaluate fracture energy, flexibility index (FI) while resistance to reflective cracking was assessed using Texas Overlay Test. Additionally, simple performance tests on control and modified HMA was  performed to evaluate resistance to permanent deformation. Results of tested modified mixtures indicated an increase in optimum asphalt content, VMA, VFA and dust proportion. All the mixtures passed the minimum threshold criteria of 80% TSR for control and modified mixtures. Experimental results revealed that a suitable proportion of CRM and PVA significantly affected the rutting and cracking performance of rubber-fiber HMA. The rubber-fiber HMA consisting of 1.5% CRM and 0.3% PVA exhibited remarkable enhancements in flow number and flow time, improving by 8 and 20 times compared to control HMA, respectively. Additionally such mixtures demonstrated approximately 1.3 and 4.5 times higher resistance to fracture and reflective cracking.  Further, digital imaging correlation analyses revealed a more twisted and convoluted fracture path and higher strain distribution in rubber-fiber HMA. The multi-functional properties of CRM and PVA were visible in scanning electron micrographs, where the rubber act as hyper elastic inclusion and properly coated fibers with asphalt, effectively bridged across cracks thus hindering the crack propagation and increased tolerance to post-peak load deformation .Finally, a detailed cost comparison and assessment of benefits was performed for both selected conventional and modified HMA mixtures. This will give transportation agencies an insight into the developed product as a valuable long-term economical alternative pavement material.