Development of hybrid polymer modified bitumen for road pavement applications
Creators: name: Joohari, Ilya
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400505
subject: Construction materials
classificationCode: 400512
subject: Transport engineering

description: The growing need for pavement rehabilitation and maintenance has led to expanding research on advances in bituminous materials. Finding innovative solutions that are sustainable, environmentally friendly and cost-efficient is a priority. An important material for pavement construction is bitumen which is composed of hydrocarbons and organic compounds. As a viscoelastic material, the behaviour of bitumen is time and temperature dependant. This implies that bitumen is brittle at low temperatures and easily forms cracks under repeated loading conditions. Conversely, bitumen softens at high temperatures and is susceptible to permanent deformation under heavy traffic loads. Therefore, there is a demand to improve the durability and service life of neat bitumen as it directly affects the asphalt pavement performance. A proven solution to this issue is adopting polymer-modified bitumen (PMB). A considerable amount of research has been done for PMB using one single type of polymer. However, some drawbacks were identified as a polymer typically has a dominant characteristic which either assists low/intermediate- or high-temperature enhancement. This research aims to develop a hybrid PMB for asphalt pavements. The concept of hybrid PMB in this research involves the combination of two groups of polymers, namely elastomer and plastomer. The first group is known to provide flexibility, while the second contributes to stiffness. Styrene-butadiene-styrene (SBS), styrene-ethylene-butylene-styrene (SEBS), and crumb rubber (CR) were considered for elasticity in this study. Meanwhile, plastomers included low-density polyethylene (LDPE), linear LDPE (LLDPE), recycled LLDPE (RLLDPE) and ethylene-vinyl acetate (EVA). A comprehensive laboratory investigation was initially conducted on the polymers only to understand their material properties. The analyses consist of chemical composition, mechanical and thermal properties. At this stage of the investigation, the polymers were combined through a melt blending process at varying ratios. The combinations tested were plastomer-SBS, elastomer-CR, plastomer-CR and elastomer-plastomer-CR, respectively. It was found that SBS/RLLDPE and SBS/CR/EVA were the ones with more promising properties. In the next investigation stage, extensive laboratory work was carried out on hybrid PMB which includes softening point, penetration, elastic recovery, infrared spectroscopy analysis, thermal analysis and rheology test. An in-depth investigation of the properties of SBS combined with four different types of polyethylene was evaluated. Outcomes from the binder tests were in line with the polymer tests indicating SBS/RLLDPE-modified bitumen to have superior performance among all. Empirical tests noted the SBS/RLLDPE-modified bitumen had a higher softening point and elastic recovery, along with a lower penetration value. The frequency sweep test indicated higher complex shear modulus (G*) and lower phase angle (¿) values. Also, there was an absence of significant difference presented in the thermal and chemical composition analyses between the virgin and recycled LLDPE. As for the hybrid PMB with SBS, CR and EVA, the test results concluded that using small content of CR did not reduce the quality performance of SBS-modified bitumen. The rutting and fatigue resistance were measured through the multiple stress creep-recovery (MSCR) and linear amplitude (LAS) test, respectively. The relationship between MSCR and LAS was plotted through the Jnr value at 3.2 kPa and fatigue performance (Df). SBS/CR/S-modified bitumen is concluded to have the optimum balance performance against both fatigue and rutting. Following this, the influence of compatibilizers on the storage stability of hybrid PMB was investigated. At this stage, SBS/RLLDPE-modified bitumen was selected to be stabilized by compatibilizers such as sulphur, maleic anhydride (MA), PE grafted maleic anhydride (PE-g-MA) and reactive elastomeric terpolymer (RET). Results identified that the compatibilizers successfully formed chemical bonds and mitigate phase separation between polymers and bitumen during high-temperature storage. Finally, the long-term service-life performance of hybrid PMB was investigated. Both polymers only and hybrid PMB were aged under similar conditions using a pressure ageing vessel (PAV). Polymer degradation resulted in increasing the elasticity of SBS but have little to no effect on RLLDPE. The rise in carbonyl index and reduction of LAS fatigue parameter value indicated the stiffening effect of bitumen due to thermal oxidation. In conclusion, this research has thoroughly analysed and discussed the feasibility of adopting hybrid PMB as a sustainable and economical approach towards mitigating problems observed for conventional bitumen.