THE PROCESS OF PRODUCING RUBBERIZED ASPHALT

Rubberized asphalt is a process of incorporating crumb rubber (CRM) with asphalt paving materials. Crumb rubber consists of recycled rubber that has been reduced in sizes less than 6.3mm. Crumb rubber can be incorporated by a wet process or a dry process. In 1991, the Federal Highway Administration (FHWA) introduced standard terminology to improve the ability to communicate the experience of highway agencies when evaluating CRM processes. Figure 1 defines the terminology and summarizes it.

Figure 1

Wet Process

Wet process refers to modification of asphalt cement binder with 5-25%wt of fine tire rubber crumb modifier (CRM) at an elevated temperature. The wet process includes the blending of the crumb rubber with the asphalt. The method of blending can be divided into three categories: batch blending, continuous blending and terminal blending. Batch blending defines those wet process technologies that mix batches of CRM and asphalt in production. Continuous blending describes those wet process technologies that have a continuous production system. Terminal blending is associated with wet process technologies that have product with extended storage (shelf life) characteristics and are produced at an asphalt cement supply terminal.

Dry Process

The dry process includes mixing the rubber particles with aggregates prior to addition to asphalt. This process provides a way to blend the crumb rubber with the asphalt and aggregate without the use of the special equipment needed in the wet process. There are some technical problems associated with this method, but new technologies are being introduced that are improving the process. Currently, the only process approved for use by the California Department of Transportation (Caltrans) is the wet process.