The blending of crumb rubber with asphalt cement has been in practice for years and a number of manufacturing processes have been developed in Europe as well as in the United States. However, all these processes have a major drawback; the asphalt rubber binder must beused within a few hours after being manufactured. In 1987, Beugnet, a road contractor in France, designed a new rubberized asphalt formula. This new formula improved rheological properties of the asphaltrubber binder, including increasing the shelf life of the binder for up to 8 days. Therefore, this new asphalt rubber binder could be used just like coventional asphalts or polymer-modified asphalts. Thedry system of rubber-modified asphalt concrete has historically been limited to only a patented process. Major drawbacks of this systeminclude the addition of crumb rubber to a unique "gap-graded" aggregate gradation, and nonconventional design criteria. These factors contribute to the high cost of using the material when compared with conventional asphalt concrete. The dry system of rubber-modified asphalt concrete has also experienced a major advance.
Abstract