Promoting resource conservation in road flexible pavement using jet grouting and plastic waste as filler

The circular economy aims to change the paradigm in relation to the linear economy by limiting the environmental impact and waste of resources, as well as increasing efficiency at all stages of the product economy; the recent warnings about waste pollution and the limits of natural resources are encouraging its development. The purpose of this research is to investigate the potential environmental and mechanical benefits of reusing two different waste, namely jet grouting waste (JGW) and plastic waste (PW) for producing hot asphalt mastics made up of bitumen and filler: the JGW comes from the soil consolidation activities during pavement construction, while the PW, a mixture of high-density polyethylene, low density polyethylene, polypropylene and polyethylene terephthalate derives from a plastic recycling plant. First, three mastics engineered by keeping constant viscosity and a filler over bitumen ratio of 0.3 for the asphalt mastic with limestone filler (LM), 0.29 for the mastic with JGW (JGWM) and 0.1 for the solution containing PW (PWM), were investigated through a dynamic shear rheometer to explore their rheological behavior. Second main step concerned the life cycle assessment (LCA) of the three asphalt mastics that, in turn, are included into the base layer of a flexible road pavement by following ReCiPe impact assessment methodology. Primary results in terms of mechanical performance demonstrated that: 1) JGWM outperformed LM in terms of complex shear modulus, which resulted 19% higher than that of LM in the temperature range below 30 °C, and 2) PWM returned on average 30% lower non-recoverable creep compliance at 50 °C under 0.1 and 3.2 kPa than remaining solutions under analysis. LCA outcomes showed, on the one hand, that PWM had the best environmental performance, expressing the lowest damage to human health, ecosystems and resource availability indicators, returning on average 34% and 19% lower indicators than LM and JGWM, respectively. On the other hand, JGWM still represented an overall improvement of the environmental performance compared to LM, returning the best performance in terms of damage to human health, which lowers by 23%, due to the reduction of the output waste stream.