Blending efficiency evaluation of plant asphalt mixtures using fluorescence microscopy

With the use of high percentage recycled asphalt pavement (RAP), there is an increasing concern over how much of the aged binder in RAP that can be blended into virgin binder. In this study, a laboratory procedure was proposed based on fluorescence microscopy for quantifying the mobilization rate of aged binder in plant-produced RAP mixtures. This procedure was derived from the mean gray value of an asphalt-coated aggregate particle. A linear blending chart was developed and used to relate aged binder content to the mean gray value of binder blend. The mobilization rate of aged binder was calculated on the basis of surface area proportion of aggregates with different size. Three types of asphalt mixtures, including one warm mix with foaming technology, two hot mixes with or without rejuvenator, were used to validate the proposed method. Results indicated that the mobilization rate varied by aggregate type (virgin or RAP). Compared with hot mix, warm mix with foaming technology showed a slightly higher mobilization rate.