Performance assessment of recycled waste materials for use in unbound pavement Layers: A case study from Turkey

Construction and demolition wastes (CDW) have become uncontrollable due to population expansion, fast urbanization, ongoing technological advancements, and changing building materials throughout time, as well as the storage of these wastes and the environmental degradation they create. In addition, recently, the depletion of natural resources and rising expense of waste disposal have increased the importance of recycling and reuse of waste. Recycling and reuse of CDW can reduce the rate of depletion of natural aggregate resources, landfill area and carbon footprint. However, the lack of knowledge about parent concrete's qualities, such as compressive strength, is one of the most significant barriers to using these waste materials. In addition, further research is needed on the use of high-strength building waste that was devastated by earthquakes and floods as aggregates. The study aimed to investigate the quality of waste concrete and assess the usability of mixtures prepared using recycled aggregates obtained from waste concrete with a predetermined strength of 35-40 MPa in combination with crushed limestone aggregate in granular road base and sub-base layers. The engineering performance of RCA will be evaluated, along with a comparison to natural aggregate, and its compliance with the limit values given in the Turkey Highways Technical Specifications (THTS) will be examined. 5 different mixes were created by replacing RCA with LA at 0%, 25%, 50%, 50%, 75%, and 100%. The strength, durability and hydraulic properties of the prepared mixtures were investigated. It was concluded that the use of RCA had no negative effects on the mixture's properties, with the exception of permeability, and even outperformed natural aggregate in terms of soaked and unsoaked CBR, CBR strength after a freeze-thaw cycle, and modulus of elasticity. Additionally, it was established that RCA satisfies the standards set in the THTS for the materials to be used in granular road base and sub-base layers.