Reflective Cracking Study: First-level Report on HVS Testing on Section 587RF - 45 mm RAC-G Overlay

This report is the third in a series of first-level analysis reports that describe the results of HVS testing on a full-scale 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 third HVS reflective cracking testing section, designated 587RF, carried out on a 45 mm half-thickness RAC-G overlay, which was included as a control for performance comparison purposes. 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 March 15, 2005 and was completed on October 10, 2005. A total of 2,024,793 load repetitions, equating to 66 million ESALs and a Traffic Index of 15, was applied during this period. A temperature chamber was used to maintain the pavement temperature at 20°C±4°C for the first one million repetitions, then at 15°C±4°C for the remainder of the test. A dual tire (720 kPa pressure) and bidirectional loading with lateral wander configuration was used. Findings and observations based on the data collected during this HVS study include: • On completion of testing, the surface crack density was 3.6 m/m2. Cracking on the overlay was predominantly transverse, as was that on the underlying layer. The crack patterns of the two layers did not match exactly; however, the areas of most severe cracking corresponded. • The average maximum rut depth across the entire test section at the end of the test was 18.2 mm. The rate of rutting was relatively slow during the early part of the experiment, but increased significantly after the 100 kN load change, despite reducing the pavement temperature to 15°C±4°C. • Both of the failure criterion set for the experiment were reached within 100,000 load repetitions of each other. • Ratios of final-to-initial elastic deflections show that damage had increased significantly at all depths in the pavement structure by the end of trafficking, with loss of stiffness highest in the area of most severe cracking in the underlying layer. • Analysis of surface profile and in-depth permanent deformation measurements indicate that most of the permanent deformation occurred in the asphalt-bound surfacing layers (overlay and cracked DGAC) with approximately twice as much damage occurring in the area of most severe cracking in the underlying DGAC layer. Permanent deformation was also recorded in the upper part of the aggregate base in this area. Negligible deformation was recorded 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.