Characterization of HMA mixtures containing high recycled asphalt pavement content with crumb rubber additives

Abstract

As the price of petroleum and material costs escalate and pressures of maintaining the sustainability of our environment, owners must continually find methods to decrease material costs and maximize their benefits. One such method is to increase and/or begin using readily available recycled materials like reclaimed asphalt pavements (RAP) and crumb rubber (CR). The objective of this study was to fundamentally characterize the laboratory performance of conventional HMA mixtures and mixtures containing high RAP content and waste tire crumb rubber/additives through their fundamental engineering properties. A Superpave l9-mm nominal maximum aggregate size (NMAS) Level 2 HMA mixture meeting LADOTD specification was designed and examined. Siliceous limestone aggregates and coarse natural sand that are commonly used in Louisiana were included in this study. Comparative laboratory evaluations of a total of six mixtures were examined in this study. Three conventional mixtures that contain an unmodified asphalt cement binder and styrene-butadiene-styrene polymer modified asphalt cement meeting Louisiana specifications for PG 64-22, PG 76-22M, and PG 76-22M respectively. The fourth mixture contains no RAP, 30 mesh CR plus additives blended (wet process) with a PG 64-22 yielding a PG76-22. The fifth mixture contains 15 percent RAP and PG 76-22M asphalt cement binder. The final mixture contains 40 percent RAP, 30 mesh crumb rubber and additives blended (dry process) with a PG 64-22 asphalt cement binder. The CR and additives were introduced to the mixture at a rate of ten percent by total weight of asphalt cement binder. To evaluate performance, physical and rheological tests were evaluated on asphalt binders. In addition, hot mix asphalt mixture performance and characterization tests namely, Semi-Circular Bend, Dissipated Creep Strain Energy, Dynamic Modulus, Flow Number, and Modified Lottman test were conducted to define permanent deformation (stability) and the fatigue life (durability) of HMA mixtures considered in this study. For the mixtures evaluated, results indicate that the addition of CR additives as a dry feed to carry rejuvenating agents is promising. The HMA mixture containing 40 percent RAP, PG 64-22, and CR additives performed similar to conventional mixtures containing PG 76-22M asphalt cement binder.