Fatigue resistance of waste plastic-modified asphalt

Recycling of waste plastic is the only truly sustainable solution for today’s environmental concerns as it represents the most concrete action to reduce the impacts of such material (Milios et al., 2018). However, due to the inherent complexity and variability of its nature, there are still significant challenges related to the management of different waste plastics. The development of new industrial technologies for the collection, distribution, and reprocessing of waste plastic are leading to new solutions for its recycling, including their use in pavements. The recycling sector today constitutes one of the most dynamic areas in the plastics industry (Hopewell et al., 2009). Very different recycling processes and methods have been investigated and an ever-increasing number of experimental applications of recycled plastic waste have been evaluated. Researchers are exploring alternative methods and materials to repurpose waste plastics that can be utilized in civil infrastructures, such as wood–plastic composites, concrete blocks, and mortars. Also, incorporating plastic waste into asphalt pavements is today a possible and sustainable practice. Several studies have verified that specific polymers and plastics can effectively improve the performance and the durability of the road pavements if adequately blended with bitumen according to certain construction and service conditions. Generally, the integration of polymers and modifiers of various nature in asphalt concrete can be either performed according to the so-called “wet” or the “dry” methods. In the first one, the modifier is added at a high temperature to the bitumen, which is accordingly referred to as polymer-modified Bitumen (PmB). Instead, according to the second one, the modifiers are added during the mixing phase of the asphalt concrete, together with aggregates and bitumen; the final product is therefore referred to as Polymer-modified Asphalt (PmA). While PmB has become common practice (e.g., styrene-butadiene-styrene (SBS) and styrene-butadiene rubber), taking advantage of waste plastics in asphalt pavements (which are usually added through the dry method, PmA) is an interesting but still challenging task for researchers and practitioners. On one hand, the adoption of various types of waste materials should be pursued to reduce the environmental impacts and save raw materials. On the other hand, researchers must prove that the use of recycled materials in large amounts allows achieving similar or improved performances when compared to traditional bituminous mixtures. Overall, the goal is to balance the environmental benefits given by the adoption of the recycled materials with the impact on the performance of the bituminous mixtures, making the most of the physical, and mechanical contributions of the incorporated recycled materials. This chapter investigates the state-of-the-art of waste plastic in bituminous mixtures for pavements with a specific focus on the effects on fatigue resistance.