Investigation of Asphalt Pavement Mixture Blending Utilizing Analytical Chemistry Techniques

The use of Reclaimed Asphalt Pavement (RAP) in new pavement mixtures is a topic of interest throughout the transportation industry and academia due its economic and environmental implications. There is concern however about how well the binder from the RAP blends with new, virgin binder when the mixture is created. Insufficient blending of the aged and unaged binders may compromise the long-term pavement performance. In this study, an enhanced staged extraction method is coupled with two chemical testing techniques to develop a novel approach for evaluating blending efficiency from a qualitative and quantitative perspective: Gel Permeation Chromatography (GPC) and Fourier Transform Infrared Spectroscopy (FTIR). Both chemical testing techniques can be used to study asphalt binder aging.

The staged extraction method consists of washing an asphalt mixture with solvent to remove layers of asphalt binder from the binder film. The study presented in Chapter 2 uses FTIR and fractionation to investigate whether sequential dissolution of the binder fractions occurs rather than a true removal of layers. Sequential dissolution is found to occur with some common asphalt solvents that were tested, and trichloroethylene (TCE) is determined to be the best solvent for staged extraction.

In Chapter 3 an approach using GPC and FTIR is used to analyze binder recovered by staged extraction to evaluate the blending efficiency of RAP and virgin binder. Partial blending of the binder is found to occur throughout the binder film. Chapter 4 explores the impact of mixing time, mixing temperature, and the addition of Warm Mix Asphalt (WMA) additives on blending efficiency using rheological testing and GPC. All mixing factors were found to impact the asphalt mixture. Blending efficiency, estimated with a blending ratio, was less than 80% in all cases.

The staged extraction method is employed with FTIR in Chapter 6 to determine the most efficient way to create a laboratory-aged artificial RAP for controlled experiments. In Chapter 7 GPC was used to develop a new method of determining whether fine aggregate used in pavement mixtures is contaminated with asphalt binder, which could potentially blend with the virgin binder and compromise the pavement performance.