Reflective Cracking Study: First-Level Report on HVS Testing on Section 589RF - 45 mm MB4-G Overlay

This report is the second in a series of first-level analysis reports that describe the results of HVS testing on a fullscale experiment being performed at the Richmond Field Station (RFS) to validate Caltrans overlay strategies for the rehabilitation of cracked asphalt concrete. It describes the results of the second HVS reflective cracking testing section, designated 589RF, carried out on a 45-mm half-thickness MB4-G overlay. The test forms part of Partnered Pavement Research Center Strategic Plan Item 4.10: “Development of Improved Rehabilitation Designs for Reflective Cracking”. HVS trafficking on the section commenced on June 23, 2004 and was completed on February 08, 2005. A total of 2,086,004 load repetitions, equating to 68.7 million ESALs and a Traffic Index of 15, was applied during this period. Temperatures were maintained at 20°C±4°C for the first one million repetitions, then at 15°C±4°C for the remainder of the test. Findings and observations based on the data collected during this HVS study include: • Some longitudinal cracking (1.55 m/m2), associated with severe deformation, was observed at one end of the section. Apart from this, no reflective cracking from the underlying severely cracked DGAC layer was observed on the MB4-G overlay after two million HVS repetitions. This implies that the MB4-G mix used successfully prevented reflective cracking. • The average maximum rut depth across the entire test section at the end of the test was 37 mm, which exceeded the experiment failure criterion of 12.5 mm reached after approximately 820,000 repetitions. As no cracking was observed, the test was continued to gain a better understanding of the MB4-G overlay performance. Despite conducting HVS testing at relatively low pavement temperatures, the MB4-G overlay appeared susceptible to rutting from early in the experiment. • Analysis of surface profile and in-depth permanent deformation measurements indicate that between 68 and 85 percent of the permanent deformation occurred in the surfacing layers with the remainder predominantly in the aggregate base layer. Negligible deformation appears to have occurred in the subgrade. No recommendations as to the use of the modified binders in overlay mixes are made at this time. These recommendations will be included in the second-level analysis report, which will be prepared and submitted on completion of all HVS and laboratory testing.