Performance Assessment of Plant-Produced Warm Recycled Mixtures for Open-Graded Wearing Courses

Abstract

Sustainable solutions, such as the combination of reclaimed asphalt pavement (RAP) as a partial substitution of virgin materials and warm-mix asphalt (WMA) additives to decrease production temperatures, represent the new research frontier in the asphalt industry. Specific investigations must evaluate the consequences of recycled WMA performance, especially in the case of open-graded (OG) mixtures, given that lower production temperatures can affect the adhesion properties and durability of those materials. This paper describes an experimental effort that involved OG mixtures produced in plant at warm temperatures (130°C) with two WMA chemical additives characterized by different compositions. In addition, an equivalent mixture (used as a control for comparison purposes) was produced at standard temperatures. Each material was prepared with a polymer-modified binder and 15% RAP. The main objective of the study was to characterize volumetric and mechanical properties of the investigated mixtures with particular attention paid to compactability aptitude and durability. To this end, gyratory-compacted specimens were subjected to several laboratory tests after dry and wet conditioning (i.e., indirect tensile strength, Cantabro test, semicircular bending, and repeated indirect tensile loading). Moreover, plant production of the investigated mixtures made it possible to evaluate the feasibility of large-scale processes. The WMA mixtures showed significant water susceptibility, although they guaranteed good compactability and satisfied mechanical acceptance requirements and international recommendations for raveling resistance in dry conditions. The chemical composition of the WMA additives was found essential to reduce the water damage. Surfactants and adhesion enhancers included within one of the investigated WMA additives ensured better water resistance than the other additive classified as a viscous regulator.