ADVANCES IN TECHNOLOGY OF ASPHALT PAVING MATERIALS CONTAINING USED TIRE RUBBER

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 be used 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 asphalt rubber 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 conventional asphalts or polymer-modified asphalts. The dry system of rubber-modified asphalt concrete has historically been limited to only a patented process. Major drawbacks of this system include 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. A rubber-modified asphalt concrete system has been developed by H. Barry Takallou. This system relates to a process for producing an asphalt concrete composition made up of coarse crumb rubber and fine crumb rubber incorporated into a standard dense-graded aggregate mixture. This process is characterized by the various constituents of the asphaltic binder and fine crumb rubber, mixed intimately by a physical reaction. This will result in a higher viscosity binder in which the optimum reaction is achieved when the fine crumb rubber particles reach optimum swelling. A pre-reaction or pre-treatment of crumb rubber with a catalyst may be needed to achieve the optimum crumb rubber particle swelling. This system can be designed using conventional testing procedures and complies with conventional design criteria. The use of this system is in the public domain.