Using RAP in slurry seals

Riverside, CA-based Pavement Recycling Systems recently completed two test projects for the City of Colton, located between Riverside and San Bernardino, using reclaimed asphalt pavement (RAP) instead of virgin aggregate in slurry seal applied to the road surface.

Don Matthews, ReNew Pavement Division manager and technical engineer for Pavement Recycling, says the company is a strong proponent of using RAP in road preservation projects and many road agency customers in the company?s Southern California market are beginning to realize the value of using RAP in surface preservation treatments.

?We?ve used RAP chip seals on smaller projects in the past; and we?ve also done some small test projects using RAP in slurry seals, scrub seals and scrub seals with RAP chip applied over the seal,? Matthews says. ?And now we?re starting to gain interest with some of the major county road agencies in our market, so I think as we continue to demonstrate the advantages of RAP preservation treatments, more prospective customers will be willing to consider RAP as a cost-effective solution to their preservation needs.?

Testing grounds

RAP aggregates for the two test projects in Colton were supplied by Reclaimed Aggregates Inc., a subsidiary of Pavement Recycling Systems. The Colton aggregate processing facility manufactures aggregate products from recycled materials - asphalt pavements and concrete.

Matthews says the company is currently producing three alternative pavement products - Rap-Seal, a RAP that has been compacted and resealed with a recycling emulsion; ReRAP, a crushed and sized RAP product that has been mixed with an emulsion before being placed and compacted; and ReNew Pavement, a RAP that has been crushed and screened into individual sizes to be blended back into a mix design that meets a specified gradation band. Performance characteristics of ReNew Pavement are comparable to conventional hot mix produced with virgin materials.

In addition to the three recycled aggregate products, the Colton facility also manufactures slurry aggregates, chip seal aggregates, concrete aggregates, and a miscellaneous crushed aggregate product that can be used on building projects instead of standard aggregate base materials.

The Colton facility is capable of producing 2,000 tons of aggregate product in an eight-hour shift, Matthews expects the facility to produce 150,000 to 200,000 tons or recycled aggregate material annually.

?We?ve spent a lot of time educating our prospective customer about recycled aggregates and we?ll continue to do so,? Matthews says. ?Like any other new product you?re trying to introduce to the market, it takes time to convince customers that recycled aggregates are just as good, and in some cases better than virgin aggregates available today.

?Recycled asphalt aggregates are good aggregates that are already coated with a protective asphalt binder, so they are a more cost-efficient source that requires less binder when constructing a new road surface,? he adds. ?In our market (California) we?re fortunate that Caltrans (California Department of Transportation) has accepted the recycled aggregate as a quality building material.

And Pavement Recycling Systems has been a strong proponent of recycling existing materials as an economical and ecological solution to maintaining the country?s infrastructure needs.

?Our objective with the Colton facility is to bring in existing material (asphalt or concrete) and process that material so that it can be used as an alternative solution. We develop new products and then work with our local (road) agencies to test the products. We approached the City of Colton to try some of the products we produce at our Colton facility,? Matthews says. ?We let them know that we?ve been testing RAP slurry seals for the past four years and the (test) roads continue to perform well to this day.?

On the one Colton project - K Street, a residential street with some moderate truck traffic, Pavement Recycling crews applied a scrub seal using 5/16-inch recycled aggregate. On the street, crews applied a PASS (Polymerized Asphalt Surface Sealer) scrub seal with RAP chip aggregate covering, and then applied a rubberized emulsion asphalt slurry (REAS) Cape Seal coating.

On the other test project - Key Street, a road serving an industrial area, crews milled three inches of the old road surface, took the material back to the Colton facility for crushing, blended the material with a latex modified emulsion, and then returned the mix to the road for cold placement.

?After the new lift was placed we then sealed one half of the road with Type II RAP slurry and the other half with Type I/Type II (REAS) rubberized emulsion RAP slurry,? Matthews says. ?County road agencies like cold in-place recycling because it?s a very economical way to rehabilitate a road that needs more than just a surface treatment.

?A cold in-place has the structural characteristics of a hot mix, but it also has more air voids that need to be sealed off if you?re not going to put down a wearing course (of hot mix),? he adds. ?That?s why on the Colton (industrial road) project we applied the sealer on the cold mix lift we placed. We also wanted to test the RAP slurry under heavy truck traffic.?

On the residential project the RAP slurry application is usually all that?s needed to maintain the road structure under the traffic load it carries, and most road agencies can?t really afford more than the occasional preservation treatment to maintain residential streets.

Slurry benefits

According to the International Slurry Surfacing Association (ISSA), the performance characteristics of a slurry mixture make an ideal preservation treatment for hot mix asphalt pavements. Materials used to create a slurry seal include aggregate (1/4-inch or smaller), asphalt emulsion, filler (Portland cement, hydrated lime or aluminum liquid serve as stabilizing agents), and water (for workability) mixed together according to a laboratory?s design-mix formula.

The emulsion serves as the binder to hold the crushed aggregate together and adhere it to the old road surface. Various emulsions and aggregates are used to meet the conditions, specifications and requirements of individual projects.

Slurry equipment, either truck-mounted or self-propelled, is used to transport unmixed materials and then blend them together in a continuous-flow pugmill. The system provides a consistently uniform mixture that can be spread over the road surface with a spreader box linked to the surface slurry-mixing unit. With mixing and spreading accomplished in one continuous operation, treated roads can be reopened to traffic within a few hours.

Emulsion of varying composition and setting times are mixed with one of three grades of aggregates - Type I (fine), Type II (general), and Type III (coarse). Fine aggregate mixtures are used for maximum crack penetration and sealing in low-density/low-wear traffic areas.

Type II aggregates are used on moderate-to-heavy traffic roads to seal, correct moderate-to-severe raveling, rejuvenate oxidized surfaces, and improve skid resistance. Coarse aggregate slurry mixtures are used to correct severe surface conditions and improve skid resistance on roads with heavy traffic loads.

Promoting the RAP advantage

?We?ve done cold placement for years and we?ve also placed thin overlays on projects that we know can last for up to 15 years,? Matthews says. ?Now, we?re trying to introduce another alternative (RAP) into the options we can make available to our customers; and we believe it will deliver the same economical performance that our other preservation methods provide.

?It?s not uncommon for us to save customers 50 percent over conventional rehabilitation methods, and we think RAP products will continue to help our customers maximize their investments,? he adds.

While some of Pavement Recycling road agency customers have experimented with RAP preservation treatments, Matthews expects more to investigate the potential performance and economic advantages of RAP preservation treatments.

?Using RAP requires less emulsion and the agencies we?ve worked with like the darker look of surface treatments that contain RAP aggregate,? he states. ?Our customers realize there is a shortage of quality aggregates in Southern California, so if we can deliver an alternative product that performs as well as a standard aggregate material, they?re willing to consider it.

?In 2007 we used approximately 6,000 tons of RAP aggregates in slurry and chip seal applications, and we expect that to increase to 20,000 tons this year,? he adds. ?We believe and many of our (road agency) customers believe it?s a viable solution to meeting the infrastructure maintenance needs of our area.?