Recycling concrete content has become an important issue for the tilt-up industry. Stapleton Enterprise Park, Denver, Colo., which currently tops the list as the greatest use of recycled aggregates for a tilt-up structure, used 2305 tons of recycled content in the wall and foundation mixes. The 441,000-square-foot office park project is part of the redevelopment of Denver's former Stapleton International Airport, and the recycled aggregates used were drawn from 6.5 million tons of material that once comprised the airport's runways. Not only did the proximity of the recycled material give the project an extra environmental boost toward Leadership in Energy and Environmental Design (LEED) certification, but it also helped keep costs low. In addition, the use of recycled material allowed the concrete admixtures to be tailored to the needs of each part of the project.
“Using recycled aggregates gives ready-mix suppliers greater flexibility in customizing mix designs that fulfill the needs of the project,” says Jay Hock, vice president of sales and marketing for ReCrete Materials Inc., Arvada, Colo., which mixed the concrete for the project. “Depending upon the recycled aggregate, you may be able to reduce your cement content and/or change the ratio of cement to fly ash or slag.” The foundation mix for the Enterprise Park project incorporated 620 tons of recycled aggregate and 115 tons of fly ash, while the tilt-up walls featured 1570 tons of recycled aggregate.
“We noticed little, if any, difference in the recycled material, including the ability to pump and finish,” says Marty Christensen of CAL Construction Co., Lakewood, Colo., the tilt-up and foundation subcontractor. “In fact, strengths have actually come out higher. I would not hesitate to use recycled materials again if they were available.”
This project marked CAL Construction's first experience using a recycled-content mix, and Christensen credits ReCrete, which specializes in creating recycled ready-mixed concrete, with helping the project run smoothly. “Some traits of the concrete were different due to different aggregates, cement, and admixtures, so it was a real asset to have a supplier with experience and a knowledge of mix designs that consist of recycled aggregates.”
The completed Stapleton Enterprise Park will house three industrial office buildings with office, showroom, research, assembly, and warehouse space, and highlight 10-foot-tall glass windows and a host of energy-efficient features. The office park is located with access to the city's major transportation sites and corridors, including Interstates 70 and 25, and the Denver International Airport. According to David Johnson of The Etkin Johnson Group, Denver, Colo., the real estate developer for the project, “Stapleton Enterprise Park will meet the city's growing demand for Class A warehouse/distribution and industrial flex space, while also providing businesses with a highly desirable address.”
The Tilt-Up Concrete Association (TCA) invites project submissions to be considered for a Top 10 list highlighting the “Most Recycled Concrete Content” on a project.
The list, which includes Enterprise Park, was initiated in response to the market's interest in sustainable solutions. “The use of tilt-up concrete goes a long way in achieving sustainability, thanks in large part to its durability,” says Jim Baty, TCA's technical director.
According to Baty, buildings seeking LEED certification can benefit greatly from the material and resources opportunities afforded by tilt-up construction, particularly when it's used in conjunction with recycled-content concrete. Those interested in their project being considered for the TCA's Top 10 list highlighting the “Most Recycled Concrete Content” on a project should contact the TCA.