Asphalt-Rubber and “the 5 Ws”

Who – The RPA is an international non-profit organization that promotes the beneficial use of asphalt-rubber. RPA members represent contractors, scrap tire recyclers, equipment suppliers, engineers, government agencies, academe, environmentalists and other interested persons.

What – Asphalt-rubber is a binder used in various types of flexible pavement construction including surface treatments and hot mixes. According to the ASTM definition (ASTM D8, Vol. 4.03, “Road and Paving Materials” of the Annual Book of ASTM Standards 2001) asphalt-rubber is “a blend of asphalt cement, reclaimed tire rubber, and certain additives in which the rubber component is at least 15 percent by weight of the total blend and has reacted in the hot asphalt cement sufficiently to cause swelling of the rubber particles”. In addition asphalt-rubber physical properties fall within the ranges listed in ASTM D 6114, “Standard Specification for Asphalt-rubber Binder,” [ASTM D 6114, 2009]. Recycled tire rubber or scrap tire crumb rubber is used for the reclaimed tire rubber portion of asphalt-rubber binder. The asphalt-rubber is formulated and reacted at elevated temperatures and under high agitation to promote the physical interaction of the asphalt cement and scrap tire crumb rubber constituents, and to keep the scrap tire crumb rubber particles suspended in the blend. Asphalt-rubber is typically used as either a Type 1 or Type 2 formulation. For purposes of this brochure both Type 1 and 2 are considered as equal. Asphalt-rubber is a combination of scrap tires and asphalt used as an asphalt binder. It is a material defined and specified by ASTM, as well as various state agencies and large city communities. It can be used as a seal coat or as a hot mix binder. Asphalt-rubber contains visible particles of scrap tire rubber.

When – Asphalt-rubber was developed in the late 1960’s and has been used in above mentioned states since that early development. It has gone from a seal coat type material to a hot mix or warm mix asphalt binder and can be used with modern paving equipment.

Why – Asphalt-rubber was initially developed as a maintenance seal coat material to hold older cracked pavements together until an overlay or reconstruction could be accomplished. Over the years asphalt-rubber has been shown to reduce the degree and severity of cracking while being applied in thin applications. Also, it reduces maintenance and provides a smooth riding, good skid resistant and quiet surface. It has also been demonstrated to be environmentally beneficial in terms of reducing energy and CO2 emissions. In addition to this it is a good sustainable engineering use of waste tires, thus reducing or eliminating the potential negative liabilities of scrap tire piles, such as burning and the breeding ground of life threatening insects, namely mosquitoes and undesirable vermin. Given asphalt-rubber’s many overall benefits of economy, life cycle costs, environmental stewardship, and good engineering performance, it should be considered a premier pavement surfacing material.

Where – Asphalt-rubber is successfully used in many parts of the world, however, the greatest and most continuous use has been primarily in Arizona, California, Texas and Florida. Admittedly, these are in warmer climate areas of the United States; however, both Arizona and especially California have colder climate areas and have had good success with the use of asphalt-rubber in such colder climates.

Remember, don’t confuse constructability with performance.