Performance Evaluation of Laboratory Produced Polymer Modified Asphalt Mixture containing High RAP Content

Abstract

Now a day in Pakistan, many roads including Motorways and Highways are reconstructing and resurfacing. Hence, tons of asphalt have been wasted. By wasting the RAP, natural resources and major portion of our finances are depleting. The sustainability of our next generation depends upon the availability of natural resources. From the last two decades, it is a worldwide practice to use the already used materials i.e., RAP in pavement construction. Many research studies have suggested that, utilizing RAP not only reduces the wastes but also minimizes the need of natural aggregates and virgin binder. Likewise, when RAP is being used it improves the performance of pavement structure. RAP being aged material, possesses more stiffness due to various environmental effects hence making it more vulnerable to thermal and fatigue and moisture susceptible. Rejuvenators are used to decrease the viscosity of aged binder. In this study RAP is being used in percentages of 0, 30, 40 & 50 along with 1% Elvaloy Polymer and 40% RAP combinations. Marshall mix design was used to determine the OBC and volumetrics of control mix, and RAP binder content was found by ignition test method. Fatigue, Rutting and Moisture parameters of RAP modified Asphalt mix were studied using Four-point beam fatigues test, Double wheel tracker test, Indirect tensile strength test approaches, respectively. Dissipated energy approach is used to determine the fatigue property of RAP modified Asphalt mix which 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. Fatigue life of RAP content and polymer modification on asphalt mixture was found in terms of PV. PV is considered as the sole parameter to measure the fatigue property 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. Indirect tensile strength (TSR) was performed to assess the moisture susceptibility in terms of TSR (tensile strength ratio) of polymer and RAP modified asphalt mixtures. From this study it is concluded that, 30% and 40% RAP modified asphalt mixtures showed increment in the fatigue life and 50% RAP modified asphalt mix shows almost similar fatigue strength as of unmodified asphalt mixture. However, Elvaloy modified binder along with 40% RAP mix has shown insignificant effect on the fatigue life asphalt mixture. Also, 40% RAP modified and 40% RAP & 1% Elvaloy modified asphalt mixtures showed an increase of 23% and 44% in the rut resistance, respectively. Moreover, 40% RAP modified mixtures have slightly increased the moisture susceptibility of asphalt mixture, while 40% RAP & 1% Elvaloy Polymer has also increased the TSR value.