The existing pavement on a section of Interstate 25 in Colorado was milled, processed cold and placed as a base course, following the recommendations of SemMaterials technologists. Four inches of the cold recycle mix was overlaid with two 2" lifts of grade C mix and one 1.5" surface course. After the project had been in place for several years, cores were taken and tested in the lab. The lab study compared the stiffness of the recycled material with standard Indiana HMA mixes using sophisticated SHRP Superpave testing equipment.

The purpose of the evaluation was to determine how the stiffness of the cold recycled material compared to that of hot mix material. The cold bituminous pavement had been in place for several years and therefore was fully cured. The Superpave Shear Tester (SST) results demonstrated that the cold mix has a slightly lower stiffness than a standard Indiana and Virginia AC-20 HMA, but is stiffer than a standard Indiana Superpave PG 58-34 base mixture.

Based on these results, it can be concluded that a properly designed and constructed RAP mixture will have the structural stiffness necessary for use as a base mixture on high volume pavements.