Constructability Test for Cold In-Place Asphalt Recycling

Unstable subgrades are a major constructability problem for cold in-place asphalt recycling. The recycling operation is often performed by a train of equipment that mills, screens, crushes, and mixes the recycled material. This train is supported by the remaining pavement after the top has been milled off for recycling. Because the remaining pavement may be as little as 1 or 2 in. thick, good subgrade stability is required to support the train. A test is developed to assess subgrade stability using a dynamic cone penetrometer. The testing instrument is inexpensive and portable, and the initial testing program can be carried out for a typical project in 1 or 2 days. Guidelines are developed using data from a project that developed varying levels of subgrade instability during construction. The guidelines were corroborated by testing on other projects. The test may be used on projects having glacial till derived soil subgrades and in which equipment is supported by 1 or 2 in. of remaining pavement plus a soil-aggregate base. Additional research is recommended to develop test guidelines for different types of soils and different base support conditions.