UC Davis Institute of Transportation Studies

This report is the fourth 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 fourth HVS reflective cracking testing section, designated 588RF, carried out on a 90 mm full-thickness AR4000-D 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 November 2, 2005 and was completed on April 11, 2006. A total of 1,410,000 load repetitions, equating to 37 million ESALs and a Traffic Index of 13.8, 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 9.1 m/m2 and was mostly confined to one half of the section. Alligator cracking predominated on the overlay, similar to 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 15.9 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.

• Ratios of final-to-initial surface elastic deflections show that damage had increased significantly 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 measurements indicate that most of the permanent deformation probably occurred in the asphalt-bound surfacing layers (overlay and cracked DGAC) with the highest damage occurring in the area of most severe cracking in the underlying DGAC layer. No in-depth elastic deflection or permanent deformation data were collected due to problems with the MDDs. Malfunction was attributed to the loss of anchorage of the modules resulting from very wet conditions in the lower layers of the pavement and subgrade.

• Parts of the test were carried out during relatively high rainfall. This resulted in ponding of water adjacent to the section. Some pumping of fines through the cracks was noted in the final days of testing. 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.