The concept of recycling asphalt pavements has been attemptedusing a range of methods for more than eighty years. Startingwith simple concepts of crushing old pavements for use in highwayfill, the technology has progressed through numerous phases. Themost recent began in the mid 1970s when both central plant andin-place methods were initiated. Hot central plant recycling andcold in-place recycling (CIR) has gained general acceptance bymany agencies. Hot in-place recycling (HlR) has been used fornearly 50 years but public agencies have been slow to implementthe technology. However, recently developed equipment and procedureshave made HIR a very viable alternative for pavement rehabilitation.

HlR methods began with various equipment that used flames whichimpinged directly on the pavement surface then progressed throughseveral evolutions of heating methods including infrared. Thecurrent state-of-the-art is a hot-air system that overcomes theprevious limitations of shallow depth of heating, burning of thesurface, and creation of objectionable smoke.

This paper includes a technical description of HIR equipmentand methods and test results from early projects using the moremodern, efficient equipment. The data and early performance evaluationshow that the 100% recycled asphalt concrete was aged insignificantlyand had laboratory test properties equivalent to virgin hot mix.