Miscele di asfalto sostenibili con RAP e plastiche di scarto = Sustainable asphalt mixes with RAP and waste plastics

The fast growth rate in plastic waste and the rising need for sustainable road construction have caused searching for new innovative approaches, such as the integration of recycled plastics and RAP into asphalt mixtures. Plastic waste disposal poses a global challenge due to low recycling rates and high landfilling costs. However, incorporating waste plastics into asphalts offers a circular economy solution, leading to both environmental benefits and enhanced pavement durability according several studies. Likewise, RAP has gained significant attraction due to being a cost-effective and eco-friendly alternative to virgin aggregates and bitumen. This thesis aims to characterize and compare the fatigue behaviour of sustainable asphalt mixtures incorporating 50% RAP and various percentages of recycled plastics. A plastomeric polymeric compound, derived entirely from waste plastics, has been used as an asphalt modified by means of the hybrid technique. Two sets of hybrid-asphalt mixtures, named AC16-SP1 and AC16-SP2 and including respectively 0.3% and 0.5% of polymeric compound by the weight of mixture, were produced in the laboratory. A control asphalt mixture, AC16-PMB, was prepared with the same lithic structure but using a polymer-modified bitumen (PmB) employing the standardized wet method. Fatigue performances and comparative analysis among these three asphalt mixtures were assessed by performing four-point bending test under stress- and strain-controlled sinusoidal loading with a frequency of 10Hz and temperature at 20 °C. Multiple fatigue criteria were applied to determine fatigue life and compared to identify possible correlations. The first criterion considers the fatigue failure as a 50% reduction in the initial modulus, measured at the 100th cycle, according to EN 12697-24. In addition, energy ratio method and dissipated energy approach, based on energy principles, were utilized for data analysis. The results indicated that increasing the polymer content added via hybrid method enhances fatigue resistance in both stress- and strain-controlled mode tests. The comparison between wet and hybrid methods revealed similar fatigue properties among AC16-SP2 and AC16-PMB. The former exhibited slightly better fatigue properties comparing ε6 parameter in strain-controlled mode, while the latter marginally better fatigue properties based on ε6 parameter in stress-controlled mode. Overall, despite the high RAP content, sustainable asphalt mixtures with an appropriate dosage of polymeric compound added via hybrid technique represent a viable alternative for sustainable road construction, offering acceptable mechanical performances and durabilities comparable to the widely used wet technique.