A Simplified Approach to Estimate Black-Rock Portion and the Degree of Blending of Reclaimed Asphalt Pavement Bitumen without Multistage Extraction Experiments

The extent of reclaimed asphalt pavement (RAP) bitumen blending with the virgin bitumen is one of the important factors that influence the properties and performance of recycled bituminous mixes significantly. Identifying and quantifying the black-rock portion of RAP bitumen, which is necessary for the direct and accurate estimation of the degree of blending (DoB), requires multistage extraction experiments. However, these experiments are laborious, time-consuming, and require a skilled workforce, along with large quantities of RAP material and virgin aggregate. This study proposes a simplified approach to estimate the black-rock portion and DoB using blending studies and single-stage extraction experiments. Fifteen experimental combinations were considered. A dynamic shear rheometer was used to obtain the rheological properties of extracted binders. Fourier transform infrared spectroscopy and thin-layer chromatography flame ionization detection were carried out to obtain the chemical properties. Using the results obtained from multistage extraction experiments carried out on the same experimental combinations as a previous study, ρ was calculated as the ratio of the quantities of uniform binder blend and intermediate blended layer. Regression models were developed to estimate ρ as a function of mix and process variables. The proposed DoB estimation approach uses the properties of the binders extracted in single-stage extraction experiments and the ρ estimated using the regression models. The DoB was also back-calculated using a mechanistic method. The mechanistic method involved measuring the dynamic modulus of recycled mixes prepared simulating actual blending condition and back-calculating the DoB using the measured dynamic modulus, Hirsch model, and the rheological properties of RAP and virgin binders. The proposed approach was also validated by comparing the DoB estimated using the proposed method and the DoB back-calculated using the mechanistic method. A good correlation (R2=0.80) was observed between the DoB estimated using the proposed approach and the back-calculated DoB, thus validating the proposed approach.