Performance of High RAP-WMA Surface Mixtures

Warm mix asphalt (WMA) mixtures that contain high amounts of reclaimed asphalt pavement (RAP) were tested in order to assess their performance when utilized as a mixture for surface courses. This paper presents the test results. The evaluation considered permanent deformation, durability, non-load associated cracking, and moisture damage. Crushed gravel and limestone mixtures were tested with 0 to 50% RAP in conjunction with three warm mix asphalts. Test results indicated high RAP-WMA to be a potentially viable product for surface mixtures. WMA was shown capable of producing rut resistant mixtures with high RAP content. A more intriguing finding was that while increasing rut resistance the high RAP mixtures did not affect the low temperature properties as much as the high temperature properties. Mixtures with high RAP content appear to be only slightly more susceptible to thermal cracking. Warm mixes have been shown to be susceptible to water. In general it was shown that WMA technology can be used with high RAP content to produce mixtures that are more resistant to moisture damage. Increasing the RAP content generally increased the resistance of the mix to moisture damage. Gravel mixtures produced with foamed asphalt, however, did not perform well with respect to moisture damage, especially with no RAP in the mixture. Testing indicated high RAP content WMA mixes may be more susceptible to durability issues than low RAP mixes. Though this has not yet been observed in the field, it is felt that it would be prudent to undertake additional monitoring of high RAP sections, in order to ascertain if and to what extent surface durability poses a problem.