Spanish technologists carried out in the 1990’s a research regarding the design procedures and construction practice for asphalt pavements modified with tire rubber. In this project, which was partially financed by Public Funds and included in the National R+D Program, more than 3,000 specimens have been tested at the laboratory. In addition to that, about 3 km of two-lane roadway has been overlaid with crumb rubber hot-mixed asphalt concrete.
The dense-graded mixes produced by the wet process showed high laboratory and field performance. Several properties of the mix, such as the fatigue life and the resistance to permanent deformations were improved when using rubber modified binder.
The dense-graded mixes produced by the dry process were found to be susceptible to the digestion of the rubber: rubber-asphalt interaction during the transport of the mix from the plant to the paving site and while the mix is in the hopper of the paver at high temperature. This period of time that is called “digestion time” has been identified as a parameter with major influence on the performance of the mix when the dry process is used.