Use of Recycled Concrete Materials as Aggregate Base Layers
Resilient properties of aggregate systems are of paramount importance in the performance characterization of pavement structures. Resilient modulus of aggregate base layer is an important input parameter for the response analysis of flexible pavements in the Mechanistic-Empirical Pavement Design Guide (MEPDG). Resilient behavior of unbound aggregate base (UAB) is significantly influenced by the aggregate physical properties, and thus good quality aggregate is desirable for construction of sustainable and perpetual flexible pavements. Recently, there has been a movement toward using recycled materials such as recycled concrete (RC) and recycled asphalt (RA) as unbound aggregate base layer. It is well established in the literature that RC systems provide better resilient properties and superior rutting resistance compared with virgin aggregate systems (Ashtiani, 2012). However, the frost susceptibility of RC systems should be also taken into consideration in the design of flexible pavement. The propensity of recycled aggregate systems to hold moisture and therefore to cause moisture damage in the pavement structure needs to be considered. This type of damage manifests itself through the decay of resilient modulus and consequently results in loss of performance upon freezing and thawing cycles. This paper presents the mechanical and environmental properties of three different aggregate sources as UAB. Aggregate specimens were prepared at optimum moisture content and at maximum dry density and were in turn subjected to standard resilient modulus test (AASHTO T307-99) and tube section test (TST) to evaluate mechanical and environmental properties. From the laboratory test results, it was observed that aggregate specimen composed of RC had sound mechanical properties with higher frost susceptibility compared with control specimens composed of virgin aggregates.