Fatigue resistance and crack propagation evaluation of a rubber-modified gap graded mixture in Sweden

The main purpose of this study was to document the laboratory experimental program results conducted at Arizona State University (ASU) and the Swedish National Road and Transportation Research Institute (VTI) to obtain material properties and performance characteristics for a "reference-gap", "polymer-modified gap", and "rubber-modified gap" graded mixtures placed on the Swedish Malmo E6 Highway. The advanced material characterization tests of interest to this paper included: bending beam for fatigue cracking evaluation and C* line integral test along with Wheel Tracking Tests (WTT) to evaluate crack propagation. The test results were used to compare the performance of the rubber- modified gap graded mixture to a polymer-modified as well as a reference-gap mixture. The results showed that the expected fatigue life for the rubber-modified gap graded mixture was the highest followed by the polymer-modified and then the reference-gap mixture. Furthermore, the crack propagation test results showed that the rubber-modified gap graded mixture had higher resistance to crack propagation; also, it was observed that rubber-modified mix satisfied Swedish requirements of the corresponding wear layer coatings. To make an overall assessment and verify the laboratory results, it was recommended to conduct a multi-year continuous field monitoring and laboratory evaluation of the test sections.