Investigating degree of blending between reclaimed asphalt pavement and virgin binder using atomic force microscopy and focused ion beam

Adding reclaimed asphalt pavement (RAP) into asphalt mixes is a common practice and has many merits such as reducing costs and emissions. In recent decades, many state highway agencies have embarked on investigating asphalt mixes with high RAP content. As the RAP content increases, understanding how well the RAP binder blends with virgin binder becomes more crucial. Lack of knowledge on how much of the residual RAP binder actively blends with virgin binder during production is one of the reasons preventing full exploitation of RAP materials. Obviously, the amount of aged RAP binder blending into virgin binder affects the properties of asphalt mixes. A study was undertaken to investigate the degree of blending, that is, the amount of RAP binder blended with virgin binder, through atomic force microscopy (AFM) and focused ion beam (FIB). The AFM measurements were conducted on both binder samples and RAP aggregate samples; the former consisted of extracted and recovered RAP binder, virgin binder, and blended binder, while the latter covered blended RAP aggregate and virgin binder samples. AFM measurements on binders indicated that blended RAP and virgin binder, at the blending zone between RAP and virgin binder, has moduli between that of pure RAP binder and pure virgin binder. AFM was also explored to investigate the degree of blending using RAP aggregate and virgin binder, but preparation of acceptable samples for such work was not possible, in spite of extensive work in preparation of such samples through mechanical polishing and FIB.