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.
REAS may be applied with standard continuous flow slurry seal equipment or by hiring the services of a central mixing plant and its distributor trucks. Application with continuous flow equipment would be the same as applying traditional slurry seal, with an on-board mixer discharging the slurry mix into a screed for uniform application onto the pavement.
A central mix plant
Petrochem Marketing Inc. has set up a central REAS slurry mix plant in Los Angeles. From there, the company can dispatch the REAS mix in special trucks with a built-in agitator to keep the material mixed while it is being transported to the jobsite. A spreader box is attached to the rear of the truck so that the slurry mix can be deposited from the tank for spreading onto the pavement. A water tank and spray bar is also built onto the truck at the front end to dampen the pavement before applying REAS.
The advantage of this portable system is that it allows any size project to be slurry sealed, so the local agency can rent the necessary equipment and perform the application when desired. The local agency does not need to maintain a stockpile of aggregate near the project. The installation of more REAS slurry mix plants in California is planned.
The City of Los Angeles Bureau of Street Services (B.S.S.) utilizes the central mix REAS concept exclusively in their annual pavement slurry seal program. This fiscal year, July 1, 2004 through June 30, 2005, they will apply over 300 lane miles of centrally mixed REAS to their residential asphalt paved streets. The Bureau of Street Services with Petrochem has created a public/private partnership that improves street preservation through the use of pre-mixed REAS. Slurry seal projects that would take weeks to complete under the conventional method are now completed within eight hours. For every 100 miles of pavement surface slurry sealed with REAS, approximately 25,935 used tires are recycled.
This partnership provides a uniform consistent product that can be delivered on site by equipment that provides easier application and greater mobility. This innovative and effective premixed, rubberized product has economic and environmental advantages, while extending the life of valuable infrastructure.
The process and product is now a Bureau of Street Services preventive maintenance standard. The Bureau of Street Services and Petrochem Marketing Inc. were awarded the Federal Highway Administration (FHWA) 2003 Environmental Excellence Award as a result of the REAS work.
What is the life of REAS compared to traditional slurry seal? Joel Halbert, recently retired as materials engineer for the City of San Diego, has been involved with the use of this product on San Diego's streets. He states that the nearest source of crushed granite aggregate suitable for slurry seal was in the Riverside area, some 90 miles away. Before REAS, Halbert says San Diego had to reseal pavement after three or four years. But test strips of REAS placed about 4 ½ years ago in San Diego still retain the black seal coat, and it appears that the seal will last at least six years. Halbert states that the extended life of REAS over the long haul outweighs the fact that it costs approximately 15 percent more than traditional slurry seal. For that reason, the City of San Diego is spending $5 million per year for its Rubberized Emulsion Asphalt Slurry Program.
The 1998 Supplement of the "Standard Specifications for Public Works Construction" (Green Book) has added Section 600-3.2 Rubberized Emulsion Aggregate Slurry to the Specifications. The supplement can be purchased from Building News, 1612 South Clementine Street, Anaheim, CA 92802. The phone number is (714) 517-0970.
To summarize, REAS is a preventive maintenance product that provides many benefits, including the diversion of used tires from waste sites back to the streets. Another advantage is that the long-lasting, thinner, tighter, emulsion-rich, continuously black product creates a blacker surface. This provides a superior contrast with pavement markings, making them easier to see, which in turn leads to safer streets and highways for the motoring public. REAS is also more cost-effective as an asphalt pavement protection material than normal slurry seal. For all these reasons, we will probably see more rubber hitting the roads in the near future.
Information provided by the Technology Transfer Program, a unit of the Institute of Transportation Studies at the University of California-Berkley.