Effect of RAP and Binder Properties on Indirect Tensile Strength and Dynamic Modulus of Cold Recycled Foamed Asphalt Mixtures with High RAP Content

Abstract

Cold recycling with foamed asphalt is a sustainable pavement rehabilitation technology and becomes more widely applied in many countries. However, there are still some ongoing scientific debates on the issues such as cold recycling mix design, pavement structural design and analysis. Many popular mix design methods adopted indirect tensile strength (ITS) as the most important design criterion. Dynamic modulus (|E*|) representing the viscoelastic behavior which has been found in the cold recycled foamed asphalt mixtures also become a helpful parameter for accurate pavement structural analysis. For cold recycled foamed asphalt mixtures with only reclaimed asphalt pavement (RAP), RAP and virgin binder used for producing foamed asphalt may govern the performance test results. The objective of this study was to determine the effects of RAP and virgin binder properties on the ITS and |E*| of the recycled mixtures. Three RAP materials (i.e., fine, medium, coarse) and two virgin binders (i.e., PG 58-34 and PG 67-22) were selected to produce six recycled mixtures. The effects of RAP properties (i.e., gradation, fineness modulus, F-E ratio) and virgin binder performance grade (PG) on the two performance test results were evaluated. The ITS results of the mixtures with finer RAP or higher PG virgin binder tended to be higher. The |E*| result was remarkably affected by RAP gradation at most of the testing frequencies and temperatures. Mixtures with the same RAP material but different virgin binder can achieve similar |E*| results.