This report contains a summary of the laboratory fatigue tests on mixes used as overlays on the Reflective Cracking Study Test Track at the Richmond Field Station. Evaluation of the results of the laboratory study on fatigue response of the overlay mixes reported herein included the effects of mix temperatures, air-void content, aging, mixing and compaction conditions, aggregate gradation, and time of loading. Five binders were assessed, namely AR4000, asphalt rubber (Type G), and three modified binders, termed MB4, MB15, and MAC15. A full factorial considering all the variables required a total of 1,440 tests. This was reduced to 172 tests to accommodate time and fund constraints. Based on the fatigue test results for the mixes used in the overlay experiment, mix rankings for initial stiffness and fatigue life are, from highest to lowest, as follows: Initial stiffness Fatigue life AR4000-D MB4-G RAC-G MB15-G and MAC15-G MAC15-G RAC-G MB4-G and MB15-G AR4000-D Until a range of pavement types and environments are evaluated in the 2nd Level Analysis, only a general indication of the relative performance of the modified binders can be deduced. It would appear that the MB4, MB15, and MAC15 binders used in gap-graded mixes as overlays on existing cracked asphalt concrete pavements should provide comparable lives (at least) to RAC-G mixes when used in comparable thicknesses in thin layers (less than about 60 mm). Recommendations for the use of MB4, MB15 and MAC15 binders in thicker layers and as densegraded mixes await the results of the shear test results and pavement performance analyses.
