| Fatigue cracking due to repeated traffic loading is one of the major types of distress in asphalt concrete pavements. Propagation of fatigue cracks in the asphalt layer will eventually allow water to come into the pavement system, and cause deterioration of pavement structure which reduces its serviceability. Hence, description and prediction of fatigue resistance of hot mix asphalt (HMA) in an accurate manner is extremely important to flexible pavement design and preservation.;In this study, to predict the fatigue life of the pavements, a failure criterion for the simplified viscoelastic continuum damage (S-VECD) model, referred to here as GR method, is proposed. This failure criterion found to exist in both reclaimed asphalt pavement (RAP) and non-RAP mixtures and also found to be independent of the mode of loading, strain/stress amplitude, and temperature and also is effective in accurately predicting the fatigue life of the mixtures.;The direct tension cyclic test with the GR method, along with beam fatigue test, and overlay tester were used to evaluate the fatigue cracking performance of plant-produced RAP mixtures in the Northeast. The S-VECD model and the GR method also was input to the linear viscoelastic pavement analysis for critical distresses (LVECD) program to predict the fatigue behavior of the tested mixtures on thin and thick asphalt pavement structures. This study included testing on 12 plant-produced mixtures from New Hampshire and Vermont that contained RAP contents of 0% to 40% by total weight of mixture. In addition, the performance grades (PGs) of the binders that were extracted and recovered from the mixtures were determined.;In general, the addition of RAP resulted in an increase in the stiffness of the materials. The magnitude of the impact of higher RAP percentages varied with each set of mixtures. The S-VECD model and beam fatigue test data showed a loss of fatigue resistance for high percentage RAP mixtures in most of the cases. The overlay tester results showed clear drops in performance at higher RAP contents. Using the lower PG binder led to improvement in the fatigue characteristics and was found to be a convenient practice.;In another study, in order to better control of the plant production variables, all the RAP mixtures were produced in the laboratory and the fatigue and rutting performance was evaluated in terms of (1) RAP percentage, (2) asphalt content, and (3) different base binders. Fatigue properties were evaluated using the S-VECD method which was later input to the LVECD for pavement analysis. Also, for rutting the triaxial stress sweep (TSS) test was performed. In addition, binder testing was performed on binders extracted and recovered from the mixtures. The test parameters included performance grade, low temperature critical cracking temperature, and multiple stress creep and recovery (MCSR) parameters tested at a high temperature.;Among the factors reviewed, incorporating soft binder was found to be a promising strategy, because the binder test data and LVECD predictions indicated a noticeable improvement in fatigue resistance. The TSS test data did not show a significant reduction in rutting resistance. Also, as the predictions clearly showed, increasing the asphalt layer thickness can lead to improved pavement performance. The test results showed that increasing the asphalt content above the optimum asphalt binder content, even with a high percentage of RAP, is not recommended because a higher asphalt content caused significant rutting in the pavement. Furthermore, mixtures with low asphalt binder content, i.e., 0.5% below the optimum binder content in this study, turned out to be susceptible to fatigue. Therefore, the best strategy for incorporating high percentages of RAP seems to be using a soft base binder while maintaining the optimum asphalt binder content and/or increasing the asphalt layer thickness. |
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