Hydraulic and Mechanical Properties of Recycled Materials Used for Roadbed Construction.

Large quantities of aggregates are needed for use as base or sub-grade materials in road construction. With ever increasing cost of mining virgin aggregates as well as the cost of disposing waste materials, there is a strong interest in recycling wastes in road construction provided they are mechanically and hydraulically suitable and they do not impact the surrounding environment. A study was undertaken to characterize the suitability of four recycled materials in terms of water retention, hydraulic conductivity, shear strength, stiffness, and leaching characteristics relative to that of virgin aggregates. The recycled materials were reclaimed asphalt pavement (RAP), reclaimed concrete material (RCM), fly ash (FA), and foundry sand (FS). They were mixed in with virgin aggregates to create seventeen mixtures. In this paper, we report the results of mechanical and hydraulic properties of these mixtures relative to that of virgin aggregates under both saturated and unsaturated conditions. All measurements were done on specimens that have been compacted at optimal water content to a maximum density with a Gyratory compactor. The shape of the water retention curve of mixtures was similar to that of the virgin aggregates but there was a slight increase in the saturated water content with addition of finer particles from fly ash and foundry sand. Friction angle in shear strength measurements was nearly same (42º to 50º) for most mixtures but cohesion values slightly increased on addition of finer particles from FA and FS. Shear strength of most mixtures was slightly higher than that of virgin aggregates. Resilient modulus, an indicator of stiffness, increased on addition of recyclable materials in virgin aggregates especially at lower than optimal water contents. Relative to 100% virgin aggregates, it appears that all mixtures of 4 recycled materials and aggregates are suitable for use in base or subgrades under roads.