Possibilities for the Utilization of Recycled Aggregate from Railway Ballast

This article deals with the possibility of using a recycled aggregate from railway ballast and platforms for the production of cement composites with a full or partial replacement of natural aggregates. This study evaluates the physical and mechanical properties of fresh and hardened concrete, as well as its resistance to water pressure, microstructure, and environmental safety. Four concrete recipes using an aggregate at the end of its life cycle from railway ballast (0/25 mm) and from the layers under the asphalt covering of the platforms (0/32 mm) were designed, with a 100% replacement for 0/25, 55% replacement (coarse fraction) for 0/32, and 45% sand for 0/4. The results have shown a significant influence of the type of aggregate on the strength, bulk density, and watertightness of the concrete. At 28 days, the compressive strengths of mixes R250, R400, R250N, and R400N were approximately 8, 20, 30, and 35 MPa, respectively, while after 90 days they increased to 10, 22, 37, and 45 MPa. The corresponding fresh concrete bulk densities ranged from about 1.95 to 2.27 g/cm3, and the water penetration depths ranged between 16 mm (best) and 27 mm (worst) among the mixes. Analyses of aqueous leachates have confirmed that the cement matrix effectively stabilizes the contaminants contained in the recycled aggregate and that the resulting products comply with the legislative limits. This study shows that an aggregate at the end of its life cycle from railway ballast and platforms can be effectively used to produce sustainable cement composites (concrete) with suitable mechanical properties and minimal environmental risks.