Hot In Place Recycling Research

This paper is a review of the Ministry of Transportation of British Columbia’s successful experience with HIR and describes the evolution of the program over a 25-year history. The paper documents the evolution of the program that has led to an increased service life of HIR at a cost of approximately 50% less than conventional mill and fill with an estimated 30 to 40 percent reduction in greenhouses gasses. The paper describes changes to project selection criteria, preconstruction sampling and testing requirements and construction specifications that are responsible for the successful HIR program in British Columbia.

This report evaluated three test sites, located in Galesburg and Machesney Park, Illinois, and Dyer, Indiana, that were HIR treated and evaluated in-situ and in the lab. Physical and rheological properties of binder recovered from each site were obtained. Interaction plots, combining rut depth from the wheel track test (WTT) and flexibility index (FI) from the Illinois Flexibility Index Test (I-FIT), were in agreement with binder test results. Falling weight deflectometer and roughness measurements were conducted before and after HIR. The environmental assessment showed a difference in energy usage and GHGs of 3.9–17.6% and 1.3–19.2%, respectively, between a HIR process with 38 mm AC overlay and a corresponding traditional 50 mm mill and AC OL for different plant locations. Energy savings from using HIR treatments heavily depend on the surface treatment after HIR, thickness of overlay (if overlay is chosen as the surface treatment), and hauling distances for plant-produced materials needed for overlays. 

The study examined a test section built in 2002 and a control section in 2003 to compare the cost and performance of HIR with conventional milling and resurfacing. After 8 years, in-service data were used to draw some conclusions. The test and control sections performed well. The HIR section was built at less than half the cost of the conventional section. Projections showed that HIR was cost-effective and would save 40% more than the conventional method of pavement rehabilitation.