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California's Interstate 10, the “Sunset Route,” has seen a dramatic increase in traffic over the past three decades. The state's DOT (Caltrans) has addressed some of the resulting wear and tear with economical “scrub seal” repairs using 100% recycled asphalt pavement. Here, the treatment has been applied to the outside (left) lane and shoulder of the highway. Photos: Western Emulsions Inc.
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Caltrans worked with Main Street Materials and Pavement Recycling Systems to crush and screen existing stockpiles of milled asphalt into recycled aggregate chip and slurry, to retain valuable asphalt content for future repair projects.

By Paul Vandermost

PROJECT OVERVIEW

OWNER | California DOT (Caltrans)

PROJECT | I-10 asphalt pavement repair

PRODUCT | PASS CR (Chip Retention)

MANUFACTURER | Western Emulsions Inc., Dana Point, Calif.

Worsening road conditions and budget restrictions have created a significant challenge in California DOT's (Caltrans) District 8, where John Hubbs is area maintenance superintendent. The district is geographically the largest of 12 statewide Caltrans districts, with four interstates — including I-10 — and 32 state routes totaling more than 7,000 lane miles.

Running from Los Angeles to Jacksonville, Fla., I-10 is one of the country's most heavily used truck routes. Historically, Caltrans maintained its 200-mile section of this popular roadway by sealing cracks and filling potholes with cold-mix asphalt. But these treatments are labor intensive, and asphalt prices have climbed to more than $100/ton — twice what they were five years ago.

In response, Hubbs uses a rapid-fill solution that seals the entire roadway surface as well as cracks to prevent moisture from compromising the base. The three-step “scrub seal” treatment consists of “scrubbing” engineered emulsion into pavement voids with a broom, applying a layer of sand or aggregate, and rolling and sweeping the repair area to clear any loose rock. The emulsion — PASS CR from Western Emulsions Inc. — combines liquid polymer-modified asphalt with a rejuvenating agent to yield a tough but highly ductile material. It resists reflective cracking: where existing cracks are mirrored on a more brittle top course. PASS formulations have been developed for specific maintenance applications including sealing, tack coating, and fog sealing, as well as applications using recycled asphalt.

Working with recycled asphalt

Caltrans formerly used 3/8-inch black volcanic cinders in its scrub seal process. But the rising cost of cinders — reaching $54/ton this year — prompted Hubbs to seek more affordable aggregates.

Last summer, as he prepared for a 35-mile scrub seal in the Riverside/In-do area of I-10, he found a source literally down the road. Recent mill-and-overlays in the vicinity had produced 300,000 tons of used asphalt millings. Rather than pay for the recyclable material to be hauled away and resold as low-value road base, Hubbs reused it.

“The stockpile contained about 5% residual asphalt content, which meant we were sitting on approximately $7.5 million worth of asphalt liquid,” says Hubbs. “The relatively high asphalt content allowed us to save money by reducing the amount of emulsion needed in our mix design.” He estimates that using recycled asphalt for scrub seal projects will enable the district to repair 10 times as many lane miles with the same materials budget.

By collaborating with his material supplier and contractor, Hubbs maximized the value of the district's materials investment and kept valuable asphalt liquid on the road where it belonged. Using a portable crushing and screening unit, contractor Pavement Recycling Systems turned the old asphalt into two new products onsite: 5/16- to 3/8-inch chip, and a slurry that used the fine material generated by the crushing and screening operation. The contractor kept the stockpiled chip moist and cool with water to maintain workability.

To optimize chip retention during application, supplier Main Street Materials applied the emulsion in a single pass with a distributor truck, followed by sweeping. The polymer-modified product proved to be very compatible with the recycled asphalt, rejuvenating the dried aggregate to mimic the properties of new asphalt.

Caltrans crews then applied the aggregate. After an initial trial using 3/8-inch chip, the team achieved better performance with the 5/16-inch size. The emulsion adhered and set up quickly, allowing traffic to return to the highway within four hours. No sanding or blotter material was required. The team finished the job in two weeks, completing an average of 3 miles/day.

At $500,000, processing and applying recycled aggregate for the 35-mile stretch cost less than half of what Caltrans would have spent on hot-mix asphalt to repave it. Most of the recycled asphalt stockpile was used, but Hubbs is keeping the rest for future projects.

The project was completed in August 2010, and received a 2011 Innovative Project Award from the California Chip Seal Association.

— Phil Vandermost (phil@westernemulsions.com) is vice president of marketing & government relations for Western Emulsions Inc., Dana Point, Calif.