Semiflexible pavement (SFP) is a composite material composed of porous asphalt mixtures and cementitious grout substances. Numerous asphalt-grout interfacial transition zones (ITZ) exist within this material and present inherent susceptibility to cracking. However, the microstructural changes within these interfaces remain inadequately understood due to the material's complex and multiphase nature. This study investigates the microstructural characteristics of the asphalt-grout ITZ and its relationship with SFP's macroscale performance, focusing on silane coupling agent modification. Atomic force microscopy (AFM) was first employed to analyze the effects of curing age, grout strength, and interfacial modification. Then, scanning electron microscopy (SEM) analysis was used to explore the correlation between the micromorphology and macroscopic mechanical properties of the asphalt-grout ITZ. Finally, a semicircular bending test was applied to test the crack resistance of SFP after interface modification. The results show that immersion of the porous asphalt mixture specimens with the interface modifier can enhance the microscopic properties of the asphalt and cementitious grout materials. The ITZ between asphalt and grout forms a double-layer structure, with smoother interfaces observed after applying the interfacial modifier. The width of the asphalt-grout ITZ may exceed 30 μm after SFP formed for 28 days. Microcracks in the asphalt-grout ITZ were significantly reduced after interface modification. These findings provide insights into proactive strategies for reducing cracking at asphalt-grout interfaces, thereby enhancing the overall performance of SFP.

RILEM TC-279 WMR task group TG 1 studied the performance of waste Polyethylene (PE) in bituminous binders and bituminous mixtures. Several laboratories participated in this study following a common protocol. Locally sources aggregates and bituminous binder and same source of waste PE were utilized. The binder experiments showed that at high temperatures, using MSCR tests, PE modified blends had better resistance to permanent deformation in comparison to the non modified binder. Whereas at intermediate temperatures, using the LAS tests, fatigue performance of the PE blends could withstand more loading cycles under low strains; however, it could sustain less loading cycles under high strains due to the increase in brittleness. Dry process was used for the mixture experiments in order to bypass the stability and inhomogeneity experience that was observed at the binder scale. The PE modified mixtures showed improved workability and increased strength. The higher the PE dosage, the higher the ITS increase with respect to the values measured for the control materials (i.e., without any plastic waste) thanks to the improved cohesion of the plastic modified mastic. The stiffness experiments tended to show an improved performance with a lower time dependence and a higher elasticity when plastic was added. The cyclic compression tests demonstrated a reduced creep rate along with a higher creep modulus thanks to the addition of PE; similar conclusions can be drawn from the experimental findings coming from wheel tracking test. Furthermore, acceptable and often improved moisture resistance was observed for PE modified materials.

Inter-laboratory experiments were designed to evaluate the impact of plastic waste blended directly in bitumen and to assess the properties, using conventional and advanced bituminous binder testing. The blends targeted 5% of plastic waste in 95% bitumen, using two types of polyethylene (PE) primary (pellets) and secondary (shreds) waste. The experiments showed that the addition of PE waste to bitumen does not alter the chemistry of the bitumen, the blending is physical. The DSR results indicate a strong dependency on the testing temperature as at low temperatures the composite material bitumen and PE behave both elastically whereas, at higher temperatures, the bitumen becomes viscoelastic. The MSCR tests indicated that the neat binder is more sensitive to permanent deformation compared to the blends with PE. The fatigue performance using the Linear Amplitude Sweep test showed a better performance in terms of stress and fatigue life for the PE blends.