WASTE PLASTICS AS RAW MATERIAL FOR INNOVATIVE ROAD PAVEMENTS: A LIFE CYCLE ASSESSMENT

Abstract

The road pavement sector represents an opportunity to recycle plastic materials. In respect of circular and sustainable economy, it is necessary to encourage recycling and reuse, especially of plastic materials, through the consolidation of the market for secondary raw materials. In fact, plastic polymers are often added to bitumen in order to improve road characteristics, such as increasing service life or decreasing road maintenance frequency. The aim of this study is to carry out a comparative analysis of environmental impacts for different road pavements that contain different mixes of bituminous conglomerate. The bituminous mixture consists of three types: traditional pavement, pavement with SBS, and pavement with a new modifier. The first one, referred as conventional pavement, is composed of bitumen and aggregates; the second type contains SBS (styrene-butadiene-styrene)-modified bitumen. SBS is the most used polymer in road pavements because it has valuable improving properties. The third type of road pavements is formed by bitumen, aggregates and a new modifier. This one is formed by hard plastics of a polyolefin nature and graphene. Life Cycle Assessment -LCA- is a modelling tool used to quantify, characterize and compare the environmental impacts. The use of LCA tools is especially valuable in the case of innovative materials containing recycled products: it may be important for applications as result of their contribution to the reduction of consumption of raw material and non-renewable resources.  The study includes all the processes and activities of road pavements that encompass material production, laying operations, maintenance works during the pavements lifetime, and end-of-life, according to a cradle to cradle approach. Moreover, in order to make a full comparison with the traditional scenario, an extension of the system has been made to consider the incineration process of hard plastics; in this way it takes into account their traditional end-of-life (as opposed to their reuse as a secondary raw material). The incineration process has been considered in conventional pavement and pavement with SBS; on the other hand, plastic recycle process has been considered in the innovative pavement (with the new modifier). The functional unit is a measure of the performance of the analyzed product system; in this work it is 1 km of road, 15 meters wide and with a service time of 20 years. The results show that recycling plastics as a polymer for bitumen modification has the potential to be environmentally advantageous compared to other two solutions: in fact the new modifier is less impactful than the traditional system and the SBS system. The results of the analysis show that the phase of material production, including raw material extraction, is relevant to almost all the assessed impact categories. This is mainly due to the production of bitumen, which is a petroleum-based product. The investigated paving solution based on waste hard plastic recycling, produces a high performance asphalt modifier according to a circular model. This solution shows a potential mitigation of the environmental impacts in all impact categories. This is due to the performance of the mixture of plastic and graphene modified added to the bituminous conglomerate. This solution is interesting for the application of the circularity criteria of hard plastics; for this category of materials, the most sustainable end-of-life is to enter a new cycle as a second raw material, instead of incineration and the consequent emissions into the environment.