Modified Cold In-Place Asphalt Recycling

Abstract

Cold in-place asphalt recycling has been shown to be a technically sound, cost-effective, environmentally friendly method of strengthening and maintaining a wide range of deteriorating asphalt pavements. The overall process combines testing and mix design procedures, milling, processing and mixing units with microprocessor control of emulsion addition, compaction, placement of a wearing surface and quality assurance testing. In laboratory work and a number of Ontario projects during the past 3 years it has been shown that modification of the cold in-place process to incorporate new aggregate results in an improved recycled binder course with closer voids and stability control. These findings address observed conventional cold in-place asphalt recycling problems such as high residual asphalt cement content (flushing), fine mix (high percent passing 4.75 mm and 75 μm), rutting (low initial stability with emulsion system), and adequacy of in-place material thickness. Structural equivalency factors for cold in-place recycled asphalt compared with conventional binder course hot-mix asphalt have been developed. Resilient properties of laboratory and field samples have been determined with the Nottingham asphalt tester and used in standard mechanistic design programs such as BISAR. Future applications of modified cold in-place asphalt recycling to improve flexible pavements will undoubtedly include airports, which will require consideration of special features such as operational constraints.