RAP slurry fits agency's 'green' initiatives

Going 'green' and sustainability have become part of the asphalt industry's daily dialogue, so it should come as no surprise that the City of Duarte, CA, was one of the first road agencies to initiate a green pavement preservation process.

In 2003, Pavement Coatings Co. of Cypress, CA, was contracted by the City of Duarte, located 10 miles east of Pasadena, to deliver the agency's annual slurry seal program.

The road preservation contractor asked to treat one road in the project with a slurry seal containing 100% reclaimed asphalt pavement (RAP). Five years later, the performance of that RAP slurry sealed street provided the confidence city officials needed to specify 100% RAP slurry seal for all roads included in its 2008 contract.

Steve Esbenshade, Duarte Engineering Division Manager, is responsible for maintaining the quality of the city's 51 centerline miles of asphalt roadways. As a 20-year employee of the city, Esbenshade takes pride in the good service quality of all the roads he oversees in the community that's home to 22,000 residents.

"Thirty-seven centerline miles of our road system are residential roads, and our citizens expect those roads to be maintained in good condition," Esbenshade says. "100% of all of our roads have received a preservation treatment of some type; whether it is slurry, cape, HMA overlay or asphalt rubber overlay. To keep our roads in good condition, I try to schedule some type of slurry treatment every five to seven years, and I make sure that one-third of the streets scheduled for maintenance each year are residential streets."

The 2008 project

In 2008, the original street maintenance contract called for conventional slurry seal. Esbenshade, who was charged by Duarte's City Council with the task of not only executing a good road maintenance program, but to also look at ways to help the city go green by utilizing sustainable treatments that performed as well as conventional treatments.

After Pavement Coatings was awarded the contract, the contractor suggested using the RAP slurry seal based on the performance of the five-year-old test and the fact that it would help Esbenshade address the sustainability issue.

"We went back and took another look at the street we treated (with RAP slurry) five years ago and it looked like it held up well. In fact, it still had a darker (blacker) appearance than a conventional slurry-treated road," Esbenshade says. "Based on my experience with Pavement Coatings, I know they produce a high-quality RAP that is used in their slurry seals. So, I felt pretty confident in agreeing to go with 100% RAP on the 2008 slurry seal contract."

Pavement Coatings' sister company, Pavement Recycling Systems Inc. of Mira Loma, CA, produces the high-quality RAP slurry dust for the preservation contractor's projects. The recycling company invested a substantial amount of time in lab and crushing work to produce the best gradation of slurry RAP to guarantee performance and workability.

Testing and field applications have led to specific product quality control and application practices to insure that customers receive an end product of high standards. The cooperative efforts of Pavement Recycling Systems and Pavement Coatings have made it possible for both to produce a cost-effective sustainable solution for customers like the City of Duarte.

A 100% RAP slurry seal product reduces the emulsion content required in a conventional slurry seal product by 20%. The reduction in emulsion saves trucking, asphalt and crude oil.

Using RAP in slurry seal applications also eliminates the need for virgin aggregate material. While the savings in emulsion and virgin aggregate only offset the additional cost of crushing and handling the RAP material, customers are satisfied with the "green" sustainable benefits they're able to achieve, and as Esbenshade points out, "taxpayers always support solutions that recycle existing materials, which is good for the environment."

Quality control

Pavement Recycling Systems has taken a leading role in promoting the benefits of a 100% RAP slurry seal alternative in meeting the needs of road agencies charged with the task of maintaining good road systems. As virgin aggregates continue to become a scarce resource and more expensive, utilizing recycled aggregates becomes a much more ecologically sound alternative.

But as Pavement Recycling Systems and Pavement Coatings point out, there has always been the issue of consistency in the quality of RAP that has caused some reservations on the part of agencies to award contracts where 100% RAP is used in the slurry application.

Pavement Coatings, which is a division of Pavement Recycling Systems, has been able to address the quality consistency issue and deliver a competitive product because Pavement Recycling controls the entire recycling process.

Pavement Recycling Systems is a vertically integrated company that maintains complete ownership and control of the RAP slurry manufacturing process - from milling to processing the recycled asphalt pavement material to be incorporated in the slurry Pavement Coatings delivers to its agency customers.

As one of California's largest cold planning and milling operations, Pavement Recycling produces a continuous supply of recycled material. That material is trucked to the company's processing facility where it is tested, fractionated (or separated) into various components, and then ground and homogenized into a mixture of uniform properties.

At each stage of the process, a full range of QA and QC procedures are performed to maintain a consistent quality product that can then be used in slurry mixtures.

The Duarte RAP slurry seal 2008 project used 1,400 tons of RAP material, which saved 49 tons of emulsion. Using a VSS MacroPaver, Pavement Coatings' slurry crew placed 210,000 square yards of RAP slurry seal over both residential and small collector roads in eight days.

"We applied the RAP slurry over some roads that were first treated with a cape seals and other roads that just received the slurry," notes Doug Ford, manager of Pavement Coatings. "We're having success with promoting the advantages of RAP slurry preservation treatments and I think as more agencies recognize that the sustainability advantages make it the right solution for preserving and maintaining the service quality of their road systems, more will choose it as their preservation solution."

The message Pavement Coatings continues to communicate to agencies is that its 100% RAP slurry product and process conserves virgin aggregates and emulsion, while performing as well as conventional slurry.

As the asphalt industry and the agencies it serves continue to look at ways to implement sustainable practices that maximize investments, conserve valuable resources, and still deliver the quality and performance expected, Pavement Coatings is convinced its "green" slurry seal preservation solution is a win-win for its future success and the needs of its customers.

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