Development of Fatigue Predictive Models of Rubberized Asphalt Concrete (RAC) Containing Reclaimed Asphalt Pavement (RAP) Mixtures

In recent years, some by-products such as crumb rubber has been used to save money, protect the environment, and extend the life of asphalt pavements. In addition, the utilization of reclaimed asphalt pavement (RAP) is an acceptable practice in many states around the United States and many countries all over the world. However, the use of RAP containing crumb rubber has not been investigated in great detail, so it is essential to explore whether these materials have a positive effect on the fatigue life of asphalt pavement. In general, previous experience shows that the use of RAP has proven to be cost-effective, environmentally sound, and successful in improving some of the engineering properties of asphalt mixtures. Crumb rubber has also been used successfully in improving the mechanical characteristics of hot mix asphalt (HMA) mixtures in many parts of the world. Fatigue is considered to be one of the most significant distress modes in any flexible pavement which is subjected to repeated traffic loading or stress. Several researchers, for the last two decades, have developed some fatigue predictive models that predict the fatigue life of asphalt mixture in the laboratory and even in the field. However, there are no research studies in the area of developing prediction models for mixtures containing crumb rubber and RAP. For this research study, A total of 39 mix designs, including two types of aggregate source, were made and tested to perform fatigue analysis and modeling. Superpave mix design procedures were used for preparation of fatigue testing specimens. The major objective of this study was to develop a mathematical model to predict the fatigue life of rubberized asphalt concrete containing RAP and included: 1) evaluating the performance of the modified binder and mixture in the laboratory; 2) measuring the fatigue life, stiffness and dissipated energy of the fatigue specimens; 3) developing the mathematical model to predict the fatigue life of the modified composite using the conventional statistical regression analysis and artificial neural network (ANN) approaches; 4) validating the fatigue predictive models using modified mixtures made from a second aggregate source. The following conclusions were drawn based on the laboratory investigation: 1) the use of crumb rubber is effective in improving the aging resistance of rubberized asphalt concrete, 2) the addition of RAP decreased the virgin asphalt content and increased the ITS values, 3) the developed specific regression models predicted a reasonable fatigue response of mixture, and the measured and predicted fatigue values were found to be close regardless of the crumb rubber, RAP content, and even testing conditions, 4) ANN approach has been shown to be effective in performing fatigue testing data of mixture and the established ANN model was able to predict fatigue occurrence accurately