Thermochemical and microstructural assessment of polypropylene modified asphalt concrete for sustainable pavement applications

In the road construction industry, there is a growing interest in incorporating polypropylene (PP) into asphalt mixtures to enhance the mechanical properties of pavement layers and address environmental concerns related to the accumulation of plastic waste. This study investigates the effect of PP-modified bitumen on the chemical, thermal, rheological, and microstructural properties of asphalt mixtures, with a focus on how these properties impact pavement performance. PP-modified bitumen was prepared using the wet process, and its properties were characterised using thermogravimetric analysis (TGA), dynamic shear rheometry (DSR), rotational viscosity, penetration, softening point, flash and fire point, ductility, water-in-bitumen content, x-ray diffraction (XRD), and x-ray fluorescence (XRF) tests. Asphalt concrete specimens were produced with 5%, 10%, 15%, and 20% PP by weight of bitumen. Microstructural features were assessed using scanning electron microscopy (SEM). Results showed that polypropylene increased softening point (48 °C to 66 °C), viscosity (135.50 cSt to 159.95 cSt at 135 °C), and Marshall stability (8.50 kN to 14.80 kN), while reducing ductility (97 cm to < 100 cm). All stability values met the 1997 Nigerian General Specification for Roads and Bridges and the Asphalt Institute criteria. These findings demonstrate that PP modification enhances the durability and deformation resistance of flexible pavements while contributing to sustainable waste management.