UC Davis Institute of Transportation Studies

This report is the first 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 first HVS reflective cracking testing section, designated 590RF, carried out on a 90-mm full-thickness MB4-G overlay. The test forms part of Partnered Pavement Research Center Strategic Plan Element 4.10: “Development of Improved Rehabilitation Designs for Reflective Cracking.” HVS trafficking on the section commenced on January 13 and was completed on June 16, 2004. A temperature chamber was used to maintain the pavement temperature at 20°C±4°C. A dual tire (720 kPa pressure) and bidirectional loading with lateral wander configuration was used. A total of 1,981,365 load repetitions, equating to 37 million ESALs and a Traffic Index of 14, was applied during this period. Findings and observations based on the data collected during this HVS study include:

• No reflective cracking from the underlying severely cracked DGAC layer was observed on the MB4-G overlay after almost two million HVS repetitions. The MB4-G overlay thus appeared to successfully prevent any cracking in the underlying layer from reflecting through to the surface, despite final-to-initial deflections indicating that considerable damage had occurred in the asphalt layers under loading.

• The average maximum rut depth across the entire test section at the end of the test was 12.7 mm, equivalent to the Caltrans (and experiment) failure criteria of 12.5 mm. The maximum rut depth measured on the section was 19.0 mm, with a maximum rut depth of 12.5 mm reached after about 1.17 million repetitions, soon after the load increase from 60 to 90 kN.

• Ratios of final-to-initial elastic surface deflections under a 60 kN wheel load increased by between 1.9 and 3.0 times along the length of the section. The ratios for in-depth deflections show that damage increased at all depth in the pavement structure (between 1.9 and 2.2 times) by the end of trafficking. Loss of stiffness was highest in the area of most severe cracking in the underlying DGAC layer.

• Analysis of surface profile and in-depth permanent deformation measurements indicates that most of the permanent deformation (between 67 [at MDD6] and 88 percent [at MDD10]) occurred in the asphalt-bound surfacing layers (overlay and cracked DGAC) with marginal deformation in the base layer and negligible deformation in the subgrade. No recommendations as to the use of MB4-G 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.