Experimental Investigation on Rheological Properties of Recycled Asphalt Pavement Mastics

Studies have shown that rheology of asphalt mastic plays an important role in pavement performance, specifically for the case of recycled asphalt pavement (RAP) mastics which contains mostly aged binder. This study determines the rheological properties of RAP mastics and a comparison is conducted with the no-RAP binder. Influence of RAP fines on rutting and cracking performances is also studied. A performance grade PG 70-22 binder is mixed with varying percentages (10, 20, and 40 %) of crushed stone (no-RAP) and RAP fines to prepare mastics. Dynamic Shear Rheometer testing is conducted to measure the complex shear modulus G*, and phase angle δ of these mastics at high and intermediate temperatures through frequency sweep. Bending Beam Rheometer test is conducted at low temperatures (-10, -16, and -22 °C) to measure the stiffness S and relaxation (m-value). Direct Tension Test is conducted to compute the failure strain at -22 °C. Results show an improvement in rutting with the addition of RAP fines (increase in G*/sinδ), a decline in low-temperature cracking resistance (increase in S). Addition of RAP fines up to 20 % does not affect the fatigue resistance of the mastics adversely. However, fatigue cracking of 40 % RAP mastic is shown to be high (increase in G*sinδ). 40 % RAP mastic shows a smaller failure strain than the virgin binder and 40% no-RAP mastic, which indicates that mastics containing RAP are more susceptible to low-temperature cracking. To characterize the viscoelastic properties of the RAP mastics, the G* master curve is constructed at 22 °C reference temperature. RAP mastics’ master curves follow the sigmoidal function irrespective of %RAP in mastics. However master curves do not show any significant difference between RAP mastics and no-RAP mastics