New developments in hot in-place recycling of asphalt pavements.

Recycling of asphalt pavements has become a widely accepted practice, particularly in North America and Europe. Several technologies have emerged to fill the various rehabilitation needs, depending on local conditions, type of pavement, and the future use of the roadway. Both hot and cold recycling in a central plant are routinely practiced. Cold in-place recycling (CIR) and full depth reconstruction is used by many highway agencies to restore surfaces and stabilize existing roadways for future overlays. Hot in-place recycling (HIR) has been used sparingly during the past 50 years, and only since the late 1980s have acceptable processes and equipment been developed. Much of the technolgical development, experience, and HIR technology has occurred in Canada, where highway agencies have embraced the concept and equipment manufacturers have provided innovations. The paper briefly describes the development and special characteristics of the various HIR processes. It describes the development of a new heating system that combines recirculating hot air with low-level indirect infrared components. In addition, a stirring mechanism has been incorporated in the heating system to ensure more uniform heating of the loose asphalt mixture and efficient removal of any moisture. The recirculated hot air is reheated, and then incinerated, thereby providing a significant improvement in air quality compared to previous generations of HIR equipment. The data from early trials in British Columbia, Canada show that the productivity is increased and the quality of recycled pavement is improved. In recent years air quality has been a factor in the acceptance of HIR in North America. Monitoring of the quality of air released at the new heating system shows the particulate matter and other solids to be the lowest among HIR systems tested. Additional projects are currently underway in Europe using the latest version of this equipment that was developed by Martec Recycling Corporation and these may provide additional data for the presentation. (A)