Meeting the Paving Challenges of the I-405 Project Head-On

If you're a paving contractor in the Northwest, you know the weather is predictably unpredictable. It's rare to have a full week of optimal paving conditions. That's certainly been the case during the construction of the I-405 widening project, as contractors press on in an effort to complete their work before the construction season grinds to a halt.

Add a nighttime paving schedule, with cooler temperatures and a restricted paving window, and a stiffer liquid binder, required by the Washington State Department of Transportation (WSDOT), and you know delivering the project to meet the customer's expectations will require a concerted effort of all involved.

The I-405 widening project is all part of WSDOT's "Moving Washington - A program to fight congestion," which is designed to add capacity and efficiency, and improve overall safety for motorists. The corridor currently accommodates 800,000 people daily. As each constructed project builds toward the master plan, more people are efficiently and safely accommodated. Eventually, the completed project will accommodate up to 1,540,000 people daily.

The 10-year "Moving Washington" plan is WSDOT's vision of investments and priorities in integrate new capacity, efficiency tools and commute options to address congestion issues and improve the overall performance of the state's transportation system.

WSDOT's vision for the future is: "To enhance our economic vitality and personal mobility while safeguarding the environment, by continually improving our transportation system. A balanced, efficient and reliable transportation system can meet our increasing population needs and allow us to stay competitive in a global economy for the years to come."

Effective and efficient transportation is critical to maintaining the state's economy, environment and quality of life.

Since the master plan for I-405 improvements was adopted in 2002, WSDOT has focused on the worst congestion chokepoints first, coordinating all transportation modes into a working system.

Through several funding mechanism, the state has invested nearly $1.5 billion into the corridor to date. The I-405 Corridor's Renton Stage 1 Widening and Renton Stage 2 Widening projects are a continuation of the master plan strategy to address congestion chokepoints.

Renton Stage 2

As part of the I-405 corridor improvement, construction of the I-405 - I-5 to State Road (SR) 169, along with the SR 515 Interchange Project (the entire project is also known as Renton Stage 2 Widening) is currently underway.

The $83.6 million project includes a new half-diamond interchange on I-405 east of the I-405/SR 167 interchange at SR 515 (Talbot Road) to improve access to downtown Renton and relieve traffic demand on the I-405 interchanges at SR 167 and SR 169.

The Stage 2 project also includes the construction of one additional travel lane in each direction of I-405 between SR 167 and SR 169, as well as building a new Benson Road Bridge over I-405. Renton Stage 2 will add another 1.8-mile travel lane in both directions when completed.

The I-405 - I-5 to SR 169 Stage 1 Widening Project was recently completed, adding a 3-mile northbound and 3-mile southbound lane to I-405 between I-5 and SR 167, along with additional improvements to SR 167 between I-405 and SW 41st Street.

Work on the Renton Stage 2 project is managed by the I-405 Corridor Design-Builders (CDB), which is a joint venture of CH2M Hill and Gary Merliono Construction Company. ICON Materials, a division of Oldcastle Materials, is delivering the asphalt paving portion of the Stage 2 project.

ICON, a leading Northwest contractor for infrastructure and transportation construction, and paving, as well as a supplier of aggregates, sand, gravel and asphalt, was subcontracted to construct the extra travel lanes on I-405, along with milling and paving work required on the interchange roads.

Dave Gent, paving and grading division manager for ICON, says the project is moving forward despite the weather, limited paving windows, and the impact both have on working with a stiffer liquid binder.

In early October, Gent told Asphalt Contractor, that ICON paving crews had completed approximately 50% of the asphalt placement work required on the Stage 2 project. ICON's paving crew has been able to pave some of the required work during daylight hours behind barriers, but that's been limited to ramp and other ancillary work required in completing the widening project. All paving on the additional travel lane expansion has been done at night.

Andy Anderson, deputy project manager for the I-405 Corridor Design-Builders, says the project calls for approximately 25,000 tons of hot mix to build the additional travel lanes, on and off ramps, surfacing the Talbot Road interchange area traveling under I-405, and building the new Benson Road realignment section that travels over I-405.

According to Anderson, "It's a significant amount of work to complete. The next two weeks (before the end of October) will tell us whether or not we can complete this project this year or wait until next spring to do so."

Both Gent and Anderson mentioned having to use a pneumatic rubber-tire roller after Oct. 1 to achieve additional compaction of the mix. It's an equipment requirement WSDOT has to assure density of stiff binder mixes being place late or early in construction season.

"We've placed approximately 12,000 tons of mix (as of early October) of WSDOT Superpave mix and we'll continue to stay on schedule as the remainder of the season allows," Gent says.

The base and intermediate courses consist of ½-inch aggregate and PG 64-22 binder with the wearing course mix design consisting of ½-inch aggregate and a much stiffer PG 70-22 binder.

"The new travel lanes and other widening pavement structures are 8-inch-thick asphalt pavements constructed in 2-inch lifts using a Cat 1055 track paver and a Dynapac 722 72-wide double steel drum roller for breakdown (compaction) right behind the paver," Gent notes. "After Oct. 1 (per WSDOT requirements), we had to bring in a rubber-tire intermediate roller (Hyster) to achieve density because of the colder temperatures we faced during our nighttime paving operations. The stiffness of the PG 70-22 binder is temperature sensitive and the extra (massaging) compaction action a pneumatic roller provides is required in cooler paving applications."

Like many night paving operations across the country, Gent, his ICON paving crew, and the I-405 Corridor Design-Builders are restricted by the traffic needs of this vital corridor. One of the two existing travel lanes can only be closed to traffic between 10 p.m. and 5 a.m. to handle the logistical needs of the paving operation, primarily trucks delivering asphalt from ICON's Auburn, WA production facility (located 15 miles from the project) and the safety of crews working on the project.

"That means we only have an operating window from 11 p.m. to 4 a.m. to actually pave," Gent says. "With traffic still moving through the construction area and the visibility issues you have to deal with at night, we're only able to place approximately 175 tons per hour when paving a 2-inch-thick lift."

And since this portion of the I-405 corridor is one of the most heavily travelled commuter corridors in the state, both existing travel lanes had to be reopened to traffic by 5 a.m. or WSDOT would assess a penalty.

Quality control

Both Stage 2 (which is under construction now) and Stage 1 (which was completed at the end of September) are warrantee projects with quality verification the responsibility of Corridor Design-Builders.

WSDOT did perform density testing to validate placement requirements, but mix test analysis, and performance delivery is ultimately guaranteed by CDB and ICON, the asphalt producer/contractor constructing the pavement sections of the project.

Daryl Rush, CDB Quality Verification Supervisor on the Renton Stage 1 Widening Project, says WSDOT's request for proposal required posting a three-year bond to cover any performance issues that may arise after the projects are completed.

"The DOT issues the Superpave specifications for the project, but the paving contractor (ICON, who also produces the mix) must submit the mix design to be used and then perform the testing of the pavement during placement," Rush notes. "On Stage 1, all requirements were met and there were no ride smoothness penalties assessed by WSDOT."

As Rush points out, quality delivery issues like density and ride smoothness are always a concern, especially when new pavements, particular mixes with stiff binders, in the Northwest at night late in the construction season.

"As the season winds down, it's a day-by-day situation, with frequent rain and cooler temperatures limiting the time you can actually get out to pave," Rush says. "Working under an accelerated schedule, in dark conditions, and alongside moving traffic is definitely challenging, but we continue to work toward a completion objective that meets our customer's (WSDOT) expectations."