Integrated and comparative Structural-LCA analysis of unbound and cement-stabilized construction and demolition waste aggregate for subbase road pavement layers formation

A more extensive use of recycled aggregate in road construction is key to meeting the ambitious targets of the EU circular economy action plan. However, scepticism among designers, contractors and road agencies remains a bottleneck. This integrated structural-environmental study demonstrates the advantages of using recycled construction and demolition waste aggregate (CDW-RA) in substitution of primary natural aggregate (NA) for the formation of subbase layers in both flexible and semi-rigid road pavements. The structural responses of different pavements with a 0.30 m subbase layer made up of four materials, i.e., two unbound and two cement-stabilized obtained including NA and CDW-RA, were compared. The environmental-related impacts were also assessed by means of a life cycle assessment (LCA). Laboratory tests and structural design led to pavement structures with the same thickness for the upper hotmix asphalt layers, i.e., 0.26 and 0.28 m for the two unbound and the two cement-stabilized subbase materials respectively. The pavement with unbound CDW-RA subbase showed the best LCA outcomes because of the more favourable environmental performance of CDW-RA compared to NA. Although the stabilization of NA and CDWRA reduces the thickness of the top hot-mix asphalt layers by 0.02 m, the environmental benefits are outweighed by the impact associated with the usage of cement. This study encourages the use of CDW-RA in road subbase layers with similar characteristics to those investigated here. The LCA results also support the use of alternative and more environmentally friendly binders that can enhance the environmental sustainability of stabilized materials in road construction.