Before 1974, stripping in hot mix asphalt concrete was considered to be a relatively minor problem in Oregon. During the three-year period from 1974 to 1977, several problems were noted during and after construction of asphalt pavements. One of the major problems associated with asphalt pavements was its initial reduced resistance to raveling. This problem developed after the oil embargo in 1974. In recent years, problems with stripping and associated pavement deterioration have continued such that in 1983 amine-type antistrip agents were incorporated into over 20% of all projects constructed.

The state of Oregon's specification (before 1984) attempts to ensure good performance of asphalt mixtures against stripping. For example, the determining factor as to the suitability of a particular mixture against stripping has been American Association of State Highway and Transportation Officials (AASHTO) T-165, index of retained strength (IRS). If the IRS of a mix at the design asphalt content is below 70% with the asphalt and aggregate to be used in the paving, an antistrip agent is used to satisfy this requirement. A 70% minimum resilient modulus ratio after vacuum saturation and freeze-thaw conditioning is used to determine the suitability of a particular mixture against stripping.

This paper addresses the current problem of stripping in the state of Oregon. Field studies conducted in 1983 were designed to identify causes of recent raveling problems in central Oregon (high elevation and severe climate areas). The investigations involved field condition surveys and coring, reviewing project construction records, mix designs, and asphalt concrete test data (construction cores and compaction control test results), and numerous tests on cores obtained from the roadway.

From the information collected, several factors were found to be contributing to the observed raveling and recommendations made for correcting these deficiencies have been included in the 1984 specifications.