The Oregon State Highway Division (OSHD) has experienced rutting and/or ravelling pavements in Oregon Class "B" asphalt concrete in the last two decades. Some of these pavement problems have evolved from material changes or changes in construction practices. The typical agency reaction to these problems has been to make adjustments in paving mixture components and mixture characteristics. These changes to mixtures have sometimes created unexpected pavement problems. Test mixtures composed of five different aggregate gradations and up to seven asphalt cement types were fabricated in the laboratory. Several index and performance tests were performed on each mixture. These test results were compared to current OSHD paving mixture design criteria. This study concluded that a gradation slightly coarser than the maximum density gradation in the 1 - 1/4 in. fraction, and significantly coarser than the maximum density in the 1/4 - 0 in. fraction should improve mixture performance. This study also concluded that conventional asphalt is satisfactory unless environment or construction conditions dictate a need for a modified asphalt. Oregon has implemented the recommended gradations from this study. Oregon has also discontinued the use of component based modified asphalt specifications for most paving projects. Only projects with harsh environmental conditions employ modified paving asphalt, and they are under a performance based specification.

Media Info

  • Features: Appendices; Figures; Tables;
  • Pagination: 52 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00623593
  • Record Type: Publication
  • Report/Paper Numbers: FHWA-OR-MA-92-10
  • Contract Numbers: 5276
  • Created Date: Jul 31 1996 12:00AM