Environmental sustainability of recycling alternative secondary aggregates for cold recycled binder layers of road asphalt pavements

The construction and maintenance of road pavements can have adverse effects on resource consumption and environmental degradation. However, they also present an opportunity for widespread adoption of circular economy principles and innovative strategies aimed at valorise waste. This study aims to develop a comprehensive procedure for assessing the life cycle environmental sustainability of substituting a high percentage of limestone aggregates with artificial aggregates and sand from municipal solid waste incineration (MSWI) in cold in-place recycled asphalt mixtures for flexible pavements. The technical feasibility of the designed mixtures was examined by evaluating the main durability performance of the cold recycled asphalt mixtures incorporating either the artificial aggregates or the artificial sand in a content range of 25-30% by mass. Subsequently, a life cycle assessment (LCA) was conducted to identify the critical stages in the life cycle of a 1 m2, 6 cm-thick binder layer of a flexible road pavement containing the alternative aggregates. The LCA covered a 30-year analysis period and considered five main impact category indicators. The main findings indicate that incorporating the artificial aggregates and sand from MSWI enhances the durability of the asphalt layers, with the most significant benefits observed for the coarse artificial aggregates. This leads to environmental advantages, particularly in terms of reduced global warming potential, fossil resource scarcity, and freshwater eutrophication indicators, which decrease on average by 11%, with reference to the whole life cycle, from cradle to grave, and by 14%, when considering the maintenance stage alone, compared to the conventional cold recycled asphalt.