Crumb rubber is made up of rubber particles 3/8 inch or smaller produced by mechanical or cryogenic means. Traditionally, the Texas paving industry has used crumb rubber produced by grinding tire buffings, a byproduct of retreading tires. With increased demand for crumb rubber, tire processors are producing more crumb rubber from whole scrap tires.
Paving applications that use crumb rubber include seal coats (or chip seals), hot mix asphalt pavement (or flexible pavement) and crack sealer. Refer to TxDOT specification Item 300 for several requirements for tire rubber, crumb rubber-modified asphalt and asphalt-rubber.
Seal Coats or Chip Seals
Surface treatments known as seal coats or chip seals are our most common use for tire rubber. Usually a single layer of asphalt covered with a layer of rocks, seal coats provide either a new driving surface or a waterproof layer under the surface layer. Engineers choose seal coats with as much as 15 percent tire rubber in the asphalt to better hold the aggregate in place and increase durability.
This analysis compares the cost effectiveness of several typical and promising maintenance treatments used to prolong the life of asphalt pavements. The study determined that “the asphalt-rubber seal coat did the best job of reducing cracking but had the most bleeding.”
Hot Mix Asphalt Pavements
Our specifications for hot mix asphalt pavements allow the use of asphalt-rubber or crumb-rubber modified asphalt. Many of our engineers choose asphalt binders with five to fifteen percent rubber to increase pavement durability and, in some cases, provide higher ride quality, particularly by reducing noise.
We use crack sealer to extend pavement life. Some crack sealers are asphalt-rubber products with as much as 22 percent tire rubber.