Performance evaluation of recycled aggregates from concrete railway sleepers for unbound subbase and base layers

Environmental sustainability, essential for the long-term preservation of the planet and sustainable development, has driven the exploration of alternative materials to reduce the consumption of natural resources in civil engineering. To alleviate the dependence on natural quarry resources and address waste disposal challenges, various waste materials have been repurposed through reintegration into production processes, as outlined in the “end of waste” framework. This approach has enabled the use of recycled materials in infrastructure projects, particularly in road construction, by incorporating waste from construction and demolition (C&D) activities. This study investigates seven groups of recycled aggregates derived from crushing concrete railway sleepers manufactured in different years, assessing their potential for use in unbound subbase and base layers. The aggregates, with a particle size distribution of 0/31.5 mm, were analyzed according to the UNI 11531–1 standard and its related regulations to determine their geometric and mechanical suitability and identify any required adjustments for performance optimization.