By: Bill Davenport
Many state and local agencies face the daunting task of keeping pace with population growth and infrastructure needs, while also balancing sustainability requirements and stringent budget parameters.
The Colorado Department of Transportation’s (CDOT) reconstruction (and widening) project on I-225 in the Denver metropolitan area, completed by Interstate Highway Construction Inc. (IHC), Englewood, Colo., is a positive example of the agency’s and the contractor’s ability to deliver a project that meets that balance.
Located in Aurora, Colo., the 2-mile reconstruction project on I-225 (Mississippi to 6th Avenue) was significant for many reasons. Aurora has seen a steady growth in population over the years, and with a 2010 U.S. Census population count of 325,078, it is the third most populous city in Colorado. I-225 runs through Aurora, and high traffic counts, including heavy truck traffic, place high demands on the existing highway. The average daily traffic on the existing section is in the range of about 121,000 vehicles, with 6.95% being truck traffic. The new concrete pavement was designed for a 30-year life and about 41.12 million ESALs (ESAL = 18,000-lb equivalent single axle load), with 182,000 average daily traffic (6.96% trucks) projected in the design year.
Recycle, reuse
A number of improvements were needed to repair the existing grade and to meet current and future needs. The approximately $22 million project consisted of a 2-mile reconstruction of the existing asphalt-overlaid concrete structure. The project also involved expanding the facility from a four-lane, divided highway to six lanes, using new concrete pavement, median barrier, sound walls, mechanically stabilized earth (MSE) walls and soil nail walls. The project also called for storm-sewer improvement, subgrade improvements and miscellaneous roadway work items.
“We considered sustainable construction practices at bid time in order to lower the environmental impact and reduce project costs,” said Matt Randall, project manager for IHC.
“One of the biggest impacts was the ability to recycle and reutilize the existing asphalt and concrete,” said Rick Erjavec, P.E., CDOT resident engineer. The existing roadway, consisting of 8 in. of concrete with a 4-in. asphalt overlay, was 100% recycled.
“The asphalt-pavement overlay was hauled off the project site to a recycling center, while the existing concrete was crushed on-site to produce coarse aggregate and Class II backfill,” Randall said, adding, “The Class II backfill was reincorporated into the project as structural fill for storm sewer and MSE walls.
“The project design consisted of 13 in. of concrete pavement over a lime-treated subgrade,” Randall said. “We expect this will provide a long-life, economical, cost-effective pavement solution.
“The project team also worked to optimize the concrete mixture design used on the project,” Randall continued. “The final mixture design allowed reduction of the cement content through the use of 20% Class F fly ash.
“This optimized mix design reduced the disposal needs of industrial byproducts, further reduced the demand on virgin materials and helped to conserve natural resources, all while averaging over 700-psi flexural strength.”
The paving was completed in just under 14 months and earned the contractor 100% of the available bonus for strength; 100% of the available bonus for thickness; and about 30% of the ride-quality bonus. Randall said that some diamond grinding was required, mostly on the headers.
Randall said a significant change that impacted the project was the revision of the original detour design from 12-in. asphalt to 7-in. concrete. “This had a direct impact on the sustainability,” he explained.
“The detour design not only further reduced the environmental impact, but also provided a temporary pavement that could be recycled on-site,” he said. “This significantly reduced the demand for virgin materials and material trucking required for the project.”
Deeper shades of green
In all, about 30,000 tons of construction materials were produced from the recycled concrete, Randall said. “This eliminated over 2,400 truckloads of material that did not leave the site or have to be hauled in from a virgin source, which significantly reduced the environmental impact.”
How significant was the reduced environmental impact? “This equates to more than 6.5 trips around the earth and a savings of over 25,000 gal of fuel,” he said.
This sustainable design choice also reduced environmental footprint over the lifetime of the roadway by reducing the amount of construction resources, materials, energy, maintenance and rehabilitation over the roadway life cycle.
For their meritorious efforts, CDOT and IHC jointly received the American Concrete Pavement Association’s 2011 Sustainable Practices Recognition Award.
This award cites the team’s use of sustainable design and construction practices for a truly “green” reconstruction project. The teamwork and leadership on this project shows how concrete pavements can exhibit a lower energy footprint, reduce the use of fuel during construction, lower disposal needs and promote 100% recycling of existing concrete materials for use in a new concrete mix and on other project components.
Randall said the project lives up to the description of a “green highway” by being environmentally responsible and sustainable throughout all aspects, including design, construction and maintenance.
CDOT’s Erjavec also noted that the project reflects the agency’s ongoing commitment to sustainable construction practice.
“We strive to incorporate sustainability and fiscal responsibility in all aspects of our job,” he said, emphasizing that, “Every CDOT project has those goals.”
This project is an excellent example of sustainable practices and shows how concrete pavements can exhibit a lower energy footprint, reduce the use of fuel during construction, lower disposal needs and promote recyclable materials.
When asked if the IHC project is a positive example for future projects throughout the state, Erjavec said, “Yes, absolutely. We have already seen another project where the contractor is currently preparing documentation that includes sustainable practices.”
Commenting on the work completed by IHC, he said, the ultimate beneficiaries are the taxpayers and highway users.
“The project really created a win-win-win situation for CDOT as the owner, for the contractor, and of course, for the taxpayers and motorists, who have a quality pavement that also is a good example of sustainable construction practices.” R&B
About The Author: Davenport is vice president of communications for the American Concrete Pavement Association, Rosemont, Ill.
