Abstract
Reclaimed asphalt pavement (RAP) material consists of aged binder and aggregate.
Considering the higher cost of RAP mix production, it is beneficial if larger quantities of RAP can be utilized in the mixes. The present study, carried out in two universities (UTEP and IIT Kharagpur), examined different issues related to the selection of RAP content in a mix. RAP from six sources and three Viscosity Grade (VG) binders were used. Dense Bituminous Macadam (DBM) mix with VG40 bitumen was selected as the target mix. Virgin and RAP binders were characterized by conducting complex modulus, multiple stress creep recovery (MSCR), and linear amplitude sweep (LAS) tests. RAP mixes were prepared using three dense gradations and two gap gradations.
RAP contents of 0%, 15%, 25% and 35% were considered for dense gradations whereas 25%, 35% and 45% were chosen for gap graded mixes.
The mixes were tested for ITS, resilient modulus and dynamic modulus and for fatigue, rutting and moisture damage resistance. A simple approach for estimation of the properties of the blend of RAP and virgin binders was proposed. The predictive models developed for dynamic modulus and phase angle of RAP mixes have been found to be good especially for predicting the phase angle of mixes for high temperature and low frequency range. Rutting resistance of the mixes was evaluated using the flow number and dynamic creep test whereas the fatigue performance of the mixes was evaluated using indirect tensile fatigue test. Moisture damage resistance was measured in terms of Tensile strength ratio and resilient modulus ratio.
The rutting resistance of the binders and mixes increased with increasing RAP content. While TSR did not give a clear indication of the effect of RAP content on the moisture resistance, the resilient modulus ratio decreased with RAP content. Fatigue performance evaluation of typical pavement sections done using laboratory fatigue models suggested that higher RAP contents do not have a significant detrimental effect on the fatigue performance of thick layers with RAP mixes. Utilization of softer virgin binder and open graded mixes permits use of higher RAP content in the mix.
Key words: RAP, Dense and Gap gradation, Target mix, Blending, Resilient modulus, Dynamic modulus, Flow number, Fatigue
