ABSTRACT
The objective of this experiment was to evaluate cracking potential of asphalt mixtures containing RAP in the laboratory and in the field. A secondary objective of this work was to characterize the mixtures’ properties in the laboratory to determine which cracking tests might most successfully predict cracking resistance in the field. Four mixtures were placed in 100-foot test strips at the NCAT Test Track in the 2015 test cycle. The mixtures varied in terms of binder type (PG grades: 64-28 and 76-22) and recycled material content (20, 25 and 30% RAP). The mixtures were evaluated for cracking potential using five different tests: Illinois flexibility index test (I-FIT), Energy ratio from Florida, Cantabro test, Overlay test (OT) – NCAT modified and dynamic modulus test. 20 million ESALs of traffic have been applied to all sections. Laboratory results did not completely exhibit expected trends in terms of cracking potential. The mixture with the highest content of RAP and highest critical performance temperature (30% RAP, PG 76-22) was not the worst cracking performer. However, the mixture with the softest binder was the top performer. With regards to field performance, all four sections have shown no significant differences in rutting, ride quality and texture. On the other hand, after 15 million ESALs, there is significant cracking in all sections (from 6% to 19% per lane). All sections followed the expected cracking trend but the section with the highest RAP content. At 15 million ESALs, Energy Ratio and Cantabro test results have shown good correlations with field cracking performance with R2 values over 0.7.
