ASPHALT PAVING: Driving on the roof

Va.’s I-66 receives effective stone-matrix asphalt cap

Trenton M. Clark, P.E., David P. Shiells, P.E., and David A. White / June 12, 2013

Just west of Washington, D.C., I-66 in Fairfax County, Va., is one of the busiest commuter routes in the country.

Between 162,000 and 178,000 vehicles per day travel on I-66—far greater traffic levels than were expected when the road opened to traffic in 1963. A major pavement-rehabilitation project in 2011 and 2012 turned the stretch of road from a nightmare to a dream, with a smoother, quieter ride. Stone-matrix asphalt (SMA), a premium surfacing material for high-volume roadways, played a starring role in the transformation.

The nightmare
I-66 originally had two lanes from U.S. 50 to S.R. 123 and three lanes from S.R. 123 to the Capital Beltway. The pavement structure consisted of 9 in. of jointed reinforced concrete pavement (JRCP) placed on a 6-in. plain aggregate base over 6 in. of cement-stabilized subgrade. In the early 1990s, the shoulders were converted to auxiliary travel lanes between U.S. 50 and the Capital Beltway. Currently, there are three travel lanes and an auxiliary travel lane in each direction.

Prior to the construction of the new lanes in the early 1990s, traffic levels had exploded on I-66, and the pavement was in need of patching, mostly due to spalling at the joints. Since then, the original lanes of I-66 continued to deteriorate and constant patching was required. However, these patching operations created congestion, and ride quality worsened. Maintaining I-66 was a nightmare for VDOT and for the motorists experiencing the rough road and lane closures from patching operations.

VDOT began exploring ways to improve I-66. Because of the congestion, the limited number of detour routes and construction costs, reconstruction of the pavement was not a very attractive option. Patching of the concrete continued until 2008 when VDOT decided a major rehabilitation was the best alternative.

Dropping the roof
In May 2008, VDOT approached the asphalt and concrete industry associations in Virginia for proposals to rehabilitate I-66. The goal of the project was to provide a cost-effective pavement rehabilitation that will last for 20 years with a minimum of disruption to the traveling public. In addition to numerous constructability challenges with I-66, VDOT had several other megaprojects in the area that necessitated close coordination of lane closures and detours. The concrete industry proposed extensive patching and grinding the concrete surface to restore ride quality; it also proposed an option of completely removing and replacing the old concrete. The asphalt industry proposed patching with asphalt and placing a new asphalt “roof” over the pavement to shield the concrete from moisture and chemicals, thus reducing the deterioration rate of the concrete. This asphalt roof, which also would improve ride and reduce noise, would consist of a 5?8-in. thin, bonded asphalt overlay, 2 in. of SMA 12.5-mm mix and 11?2 in. of SMA
9.5-mm mix.

Trickery slope
VDOT selected the Virginia Asphalt Association’s recommendation but chose to patch the pavement with concrete instead of asphalt. In September 2010, the project was funded and advertised as a design-build project. The final pavement had to meet smoothness standards, and a minimum vertical clearance of 16 ft had to be maintained for all overpasses.

In December 2010, Fort Myer Construction Co. of Washington, D.C., was awarded the contract for $37.9 million. The Fort Myer team included many subcontractors and consultants. Fort Myer performed the concrete patching; APAC from Asheville, N.C., placed the thin, bonded asphalt overlay; and Superior Paving Corp., Gainesville, Va., produced and laid the SMA.

Work immediately began on patching the deteriorated concrete. Once patching was completed in the eastbound direction, APAC placed a 5?8-in. layer of thin, bonded asphalt overlay. The thin overlay used a polymer-modified PG 70-28 binder supplied by Nustar. Travelers along I-66 noted the immediate improvement once the thin overlay was placed. The thin asphalt overlay smoothed out the new PCC patches and leveled the surface for the placement of the first course of SMA.

After the thin asphalt overlay was placed, a leveling course was laid to correct cross slope. The first lift of SMA was a 12.5-mm mix utilizing a PG 76-22 polymer-modified binder. Finally, the second lift of SMA-9.5 was placed. Each mix used processed RAP and was produced using warm-mix foaming technology to assist in field compaction efforts.
Unlike flexible pavements that can have cross-slope adjustments made through the milling process, I-66’s deteriorated concrete could not be milled. Instead, cross-slope deficiencies had to be corrected with the asphalt overlays. After the initial lift of SMA-12.5 was paved, Superior Paving applied a targeted leveling course of Superpave-9.5 mm to re-establish a uniform cross-slope.

Finally, the SMA-9.5 paving operations began. Paving was limited to the hours of 10 p.m. to 5 a.m. to minimize inconvenience to the traveling public. Even with these restrictions, paving quantities exceeded 1,200 tons per shift. In all, Superior Paving placed 48,388 tons of SMA-12.5, 33,208 tons of SMA-9.5 and 2,102 tons of SM-9.5 scratch course. With the shoulder rehabilitation and ramp paving included, nearly 100,000 tons of asphalt was laid.

The dream realized
On Aug. 3, 2012, Superior Paving completed the SMA-9.5 surface. To meet the project requirements, not only did the mix have to meet material specifications at the plant and in the field, but it also had to be smooth. The contract established maximum project roughness and maximum individual section roughness. If the project had an international roughness index (IRI) above 70 in. per mile or an individual location had a roughness greater than 80 in. per mile, then corrective action had to be taken to provide final ride quality below these thresholds.

Prior to the project, this section of I-66 had an average IRI of 143 in./mile in the eastbound direction and 138 in./mile in the westbound direction. After the patching and overlays, VDOT performed acceptance ride testing. Overall, the ride quality in both directions was improved by nearly 200%. In fact, of the 30 lane-miles of paving, or 3,000 individual 0.01-mile sections, only 80, or 2%, of the sections did not meet the threshold of 80 in. per mile. Many of these areas were associated with the transition of the asphalt overlays to concrete under structures where clearance had to be maintained. Most were corrected by diamond grinding.

Another benefit of the new asphalt surface is noise reduction. Prior to the project, VDOT collected onboard sound intensity measurements on the deteriorated concrete. The noise levels for both directions averaged 106.7 dBa. In October 2012, VDOT collected sound measurements on the new SMA-9.5 and the adjacent PCC which was not overlaid. The concrete section was measured at 105.6 dBA, an improvement of 1.1 dBA. For the new asphalt surface, the decibel level was reduced to approximately 102 dBA—an improvement of 4.7 dBA. An improvement of 3.0 dBA is considered readily noticeable by the motorist.

The rehabilitation of I-66 demonstrates the ability to accomplish seemingly impossible projects through partnerships and innovation. The new asphalt surface provides a long-term solution for the users of I-66 and the Virginia Department of Transportation. R&B

About the Author

Clark is the director of engineering for the Virginia Asphalt Association. Shiells is the materials engineer for the NOVA (Northern Virginia) District of the Virginia Department of Transportation. White is a vice president for operations with Superior Pav

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