This project applied contemporary laboratory tests to ascertain whether increased reclaimed asphalt pavement (RAP) content negatively impacts fatigue cracking resistance when subjected to long-term aging. A key distinction is that the materials are real- world production mixtures from full-scale asphalt plants rather than laboratory-prepared mixtures. Five mixtures were characterized in all with two asphalt performance grades (PG64-22 and PG58-28) and varying RAP contents (0 percent, 15 percent, 25 percent, 40 percent).
The key project objective is to quantify the impact of reclaimed asphalt pavement content on fatigue cracking resistance.
(2013 Update) Recently the same tests applied to these plant-produced reclaimed asphalt pavement (RAP) materials were applied to new mixes designed from accelerated load facility materials. These laboratories produced mixes were well controlled and able to change only the RAP content variable and other volumetric variables were not changed to cause confounding effects. Increasing RAP contents decreased the fatigue resistance, which supports the theory that the findings below were due to other differences in the plant produced mixtures; notably the stockpiles that caused different air void content, voids in the mineral aggregate, and voids filled with asphalt at fixed gyrations. (2011 Findings) The findings of the study disagreed with the intuitive concept that increases in reclaimed asphalt pavement content reduce fatigue resistance. However, it must be stressed that the caveat of this finding applies only to these particular plant-produced materials because the variables of aggregate blending or asphalt binder chemical incompatibility could have influenced the results. Volumetric proportions showed the binder content was fixed but the individual blends of aggregates for the mixtures were different and had to be adjusted to accommodate the different RAP contents. The fatigue performance of the various mixtures was not substantially different by orders of magnitude and depending on the failure criteria utilized, the ranking between the mixtures could change. The implications of this particular study and materials, to be taken with caution, are that larger recycled asphalt pavement contents above the status quo (15 percent) do not necessarily jeopardize fatigue performance, but laboratory characterization in general is recommended. This recommendation is facilitated by Federal Highway Administration's (FHWA's) implementation of the Asphalt Mixture Performance Tester (AMPT), having the capability to perform fatigue characterization although the fatigue module is not as ready for practice as the primary capabilities for dynamic modulus to be used with mechanistic-empirical pavement design software.