Effect of relative humidity and carbonation on the mechanical behavior of compacted fine recycled aggregates

Recycled aggregates are primarily composed of concrete, natural stones, and bricks obtained through sorting, crushing, and sieving of construction and demolition waste. They offer a promising route toward reducing the consumption of natural resources and minimizing landfill use in civil engineering, thus supporting circular economy and contributing to more sustainable construction practices. This study specifically investigates the mechanical behavior of compacted fine recycled aggregates for road pavement base layers, with a focus on the effects of relative humidity and carbonation. Cylindrical samples with a compactness of 0.69 were subjected to controlled curing conditions over 30 and 100 days. Three relative humidity levels (53%, 65%, and 95%) and two carbon dioxide concentrations (0.05% representing natural conditions and 3% for accelerated carbonation) were also investigated. Additional samples were oven-dried to establish baseline mechanical properties under zero moisture content. All specimens were tested in a triaxial apparatus under confining pressures of 0, 100, 250, and 400 kPa to assess their shear strength and deformation behavior. The results indicate that higher CO₂ concentrations lead to a reduction in strength, contrary to expectations. Additionally, increased relative humidity correlates with lower peak strength and higher ductility. These findings underscore the critical influence of environmental curing conditions on the long-term performance of recycled aggregates in pavement applications.