For the past 11 years, Rubberized Emulsion Aggregate Slurry (REAS) has been successfully applied to pavements in Southern California to protect the asphalt of streets and highways, as well as parking lots and airports. This relatively new product, which incorporates finely ground rubber from discarded tires, has been well received by cities and counties throughout the state. The City of San Diego has applied over 200 million square feet of REAS over the past seven years. The Los Angeles County Public Works Department has applied this product to more than 160 million square feet of streets and highways, as well as on all the paved surfaces at El Monte Airport, including runways, taxiways, airplane tie-down areas and parking lots. Several other Los Angeles County area airports have also had REAS applications.
Local agencies report good results using REAS
According to Harry W. Stone, Los Angeles County Department of Public Works, test results indicate that REAS "has the potential to decrease the maintenance frequency for recoating asphalt surfaces while providing a highly skid-resistant surface." At El Monte Airport, for instance, the surfaces show no wear even though it has been 4 ½ years since they were applied. The sealcoat is continuing to provide uniform coverage and maintain its dark color.
Other products used to sealcoat the airport pavements have not performed this well over a comparable time period. Stone made the above statement in 1998, when at the time he was Director of Public Works for the County of Los Angeles. Approximately 3 ½ years later, Los Angeles County Public Works placed another coat of REAS on the pavement surfaces at El Monte Airport. The original REAS coating, then eight years old, was still dark and the asphalt paved surfaces were still well sealed.
To produce REAS, finely ground rubber from discarded tires is introduced into an anionic asphalt emulsion along with a polymer modifier to stabilize viscosity, setting and curing characteristics of the slurry mixture. Obviously the recycling of used tires into a useful product provides an environmental side benefit. One tire finds its way into approximately 635 square feet of REAS. This translates to more than 100 recycled tires being used for one 12 foot lane mile of seal coat.
Advantages of REAS
Four gradations of aggregate are used for REAS: Fine Aggregate, Type I, Type II and Type III. The Type I, Type II and Type III aggregate gradations are the same specifications as used in non-rubber slurry seal and have been used successfully on major highways as well as local roads.
A REAS slurry uses twice as much emulsion as is used in conventional slurry seals. A standard wet track abrasion test is necessary to certify the formulation of the REAS slurry mix. The results have exceeded the same tests for the non-rubber emulsion slurry. This translates into a longer life in the field.
Other benefits to REAS include an extremely black color due to the carbon black that is added to the rubber of tires when they are manufactured. The black color of the sealcoat is retained for over five years after application and provides a high contrast for painted traffic markings. This in turn provides for safer roads. The added polymers fortify the REAS to provide a superior water barrier to protect the asphalt pavement. Another benefit is protection from the sun's ultra-violet rays, which can deteriorate the underlying asphalt pavement.
REAS is easy to apply. Because it is used with 1/8-inch aggregate rather than 1/4-inch, it forms a thinner layer than non-rubber asphalt emulsion slurry, allowing it to set in the same amount of time as the non-rubber product. This occurs without the addition of an accelerator or retarder which often becomes necessary for non-rubber slurry seal.
Regular slurry seal develops scuff marks caused by "tire scrubbing" — turning the steering wheel when the vehicle is in a stationary position. This recurring problem requires frequent returns to the project site to reapply the slurry seal in the scuffed-up areas. Where REAS is used, very few scuffed areas require repairs.