Dissipated Energy Analysis of Asphalt Mixtures Containing Reclaimed Asphalt Pavement (RAP)

Abstract

Pakistan has very vast road network consisting of 263,775 kms, maintenance of which cost huge amount to the national exchequer. For cost effective transportation system, it is necessary to incorporate recycled material in road construction. Reclaimed asphalt pavement (RAP) which is hot mix asphalt (HMA) obtained in resurfacing or reconstruction processes. RAP is being used worldwide as construction material in new pavement including Pakistan specifically for past two decades. Use of RAP, reduces use of virgin binder and natural aggregate, and improve performance as suggested by previous studies. HMA prepared with RAP possesses more stiffness due to various environmental effects which makes it more vulnerable to thermal and fatigue cracking. Usually, to decrease the viscosity of aged binder rejuvenators are used. In this study waste cooking oil (WCO) was used as rejuvenator. HMA mixtures containing RAP up to 60% and WCO up to 5% was prepared. Marshall mix design was incorporated for determination of OBC of control mix and volumetric properties of HMA modified with RAP. Asphalt beam was prepared in rolling wheel compactor for fatigue performance evaluation. Various approaches are used to study the fatigue behavior of asphalt including phenomenological approach, the fracture mechanics and energy-based approach. Dissipated energy approach is based on the internal damage produced in asphalt mixture used in this research. Dissipated energy allows to predict fatigue life of asphalt mix without performing millions of loading cycle unlike in traditional phenomenological approaches. Dissipated energy ratio (DER) was calculated at every 100 loading cycles and a graph was plotted. Plateau value (PV), which is constant value of DER, was calculated at loading cycles corresponding to 50% of initial stiffness for each mix. PV is considered as the sole parameter to measure the fatigue susceptibility of asphalt mixtures. Higher PV indicates more fatigue susceptibility of asphalt mixture and vice versa. Four-point bending test was performed on the asphalt mixture beams at 20oC temperature and 10 Hz loading cycles. The test was performed at controlled strain mode at fixed strain level of 500ms. From this study it is concluded that HMA mixture containing 40% RAP showed lowest PV, hence highest fatigue life was observed for this mix. Volumetric properties of all the HMA mixes found to be within range and mix having 40% RAP found to be most optimized. Cost analysis shows that using 40% RAP in the mix can save up to 22% of the total cost of the HMA production. Keywords: Dissipated Energy Analysis, Four-Point Bending, Fatigue, Hot Mix Asphalt.