In 2011, after years of patching and repairing its main thoroughfare, Denver International Airport (DIA) invested $10 million in repaving Peña Boulevard. Originally built in the early 1990s, the four-lane divided highway had developed severe alkali silica reactivity damage that required costly and disruptive maintenance on a curving three-mile stretch approaching the airport.

Not only did its replacement result in a smoother ride; the project was named the 2015 Triad Award winner by Concrete Construction and its sister publications. With an impressive combination of collaboration and expertise, the project team successfully met the technical, environmental, and logistical challenges the high-profile job had in store.

Delivering sustainability

Denver International Airport, owned and operated by the City and County of Denver, awarded the project to contractor and concrete supplier Castle Rock Construction Co. of Colorado (CRCC), which has earned a reputation for expertise in concrete paving in the Rocky Mountain region since the 1980s.

Although Peña Boulevard’s original project design called for completely removing existing pavement, DIA and the contractor developed a value-engineered plan to rubblize the concrete in place, a technique the City and County of Denver has used successfully since 2011.

“When you consider the cost savings and environmental benefits like reducing pollution and using recycled material, rubblization is a win-win,” says Michael Cloud P.E., engineer and project manager of airport infrastructure management for Denver International Airport. He says rubblization costs about half as much as complete removal and produces a better product.

Concrete is broken down and compacted in three steps to create a base for the fresh pavement. This rubblized material allows for a drainable base to relieve trapped water, which will help prevent future settlement and distresses in the pavement structure.

To complete the stabilized road base, the contractor added 2 inches of Class 6 aggregate. “We had an unexpected 10% overrun on base course aggregates, due to voids created during the rubblization process,” says Gary Ungerman, manager of business development for CRCC. Base course aggregate was recycled onsite or brought in from the airport’s recycling yard, where concrete removed from the airfield and other areas is crushed and stored for reuse.

Use of recycled construction materials has increased in Colorado since 2007, when Governor Bill Ritter, Jr. issued Greening of State Government, an executive order to reduce the environmental impact of government activities. In response, the Colorado Department of Transportation (CDOT) created an industry task force to develop a “green concrete” paving specification, involving industry leaders such as CRCC and Holcim (US) Inc.

The new specification, adopted in 2008, allows carbon-reducing alternatives to traditional cement, such as fly ash and portland-limestone cement (PLC), to be used in paving projects (via the ASTM C1157 performance cement specification, prior to the creation of ASTM C595 IL in 2010).

Portland-limestone cement contains between 5% and 15% limestone, and has performance characteristics similar to conventional portland cement. “PLC doesn’t change how concrete is produced, but it reduces the material’s overall carbon footprint by reducing the amount of clinker used, and the energy associated with its production,” says Brooke Smartz, LEED AP and senior market manager, sustainable products for Holcim (US) Inc.

CRCC became convinced of PLCs reliability after initial concerns about strength. “We weren’t sure we’d earn Colorado’s financial incentive (an additional 3% payment) for meeting 650 psi flexural strength, using PLC instead of Type I/II cement,” says Ungerman. “But since we’ve been working with Holcim we’ve always been able to meet it without a problem.”

Smartz worked with CRCC on the first PLC concrete paving project in the state (U.S. Highway 287) — and the partners have since designed mixes for more than 300 lane miles of PLC pavement, including Peña Boulevard.