The Urban Quarry

Features - Cover Story

The former Stapleton Airport in Denver yields a massive recycled aggregates lode.

December 3, 2002

The former Stapleton Airport in Denver yields a massive recycled aggregates lode.

The scope of the project is overwhelming. Six million tons of runway, taxiway and concourse concrete and asphalt. Fleets of trucks, loaders and several pieces of recycling and screening equipment. Hundreds and hundreds of feet of conveyors. Six years to process the material and 10 years to use and market it.

There were probably dozens of reasons why Recycled Materials Co. (RMC), Arvada, Colo., could have backed off from its proposal to recycle the runways, taxiways and parking lots of the former Stapleton International Airport in Denver.

But CEO Ken Buesing, president Mark Wachal, general manager Rick Givan and the company’s other leaders didn’t back away from the project. Instead, they have followed up on every commitment and turned the former airport into a bold experiment in urban quarrying.

In the second half of 2002, RMC entered its fourth year of concrete and asphalt recycling at Stapleton, continuing on a project that produces up to 5,000 tons of secondary aggregates each day.


There have been very few new airports built in the U.S. in the past two decades, and thus very few old airports taken out of service.

But civic planners in the Denver area made the decision to build a major new airport at a greenfield site and to shut down operations at the former Stapleton International Airport.

While commercial airport closings are rare, the scaling back of the number of military bases in the past 10 years has resulted in several military airfields being de-commissioned.

One of the de-commissioned sites was Lowry Air Base, also in Denver. When this Air Force training center and airstrip was closed down and re-developed, Recycled Materials Co. was a key part of the demolition and development process.

"Lowry was a major military base that was scheduled to shut down," says RMC general manager Rick Givan. "At the time it happened, the company was involved in several contracting segments, but the one our president Mark Wachal wanted to focus on was concrete recycling," he adds.

The company was the winning bidder for several contracts at the Lowry site, and it eventually recycled parts of runways and roadways and also built a sports complex and some of the roads in the neighborhood being developed at the former air base site.

Givan says the company’s experience with the Lowry project was helpful in several aspects to prepare RMC for the Stapleton project that would lie in its future. "We learned a good deal about government applications and proposals, about working with future users and about finding applications for recycled concrete and asphalt," notes Givan.

In the mid-1990s, as construction of the new Denver International Airport proceeded, a committee was formed by the City of Denver to begin making plans and holding public forums concerning the redevelopment of the seven square miles of land comprising Stapleton Airport.

The committee and the resulting Stapleton Development Foundation consisted of elected officials and citizens from surrounding neighborhoods as well as business owners and executives with land planning experience.

Mark Wachal, with his Lowry redevelopment experience and knowledge of materials recycling techniques, attended the public forums and eventually served with the foundation. His involvement with the foundation was key to ensuring that the recycling of demolition materials generated at the airport remained on the redevelopment agenda.

Ultimately, Recycled Materials Co. had to bid against several major contracting and engineering firms in 1998 for the right to remove and recycle the estimated 6 million tons of concrete contained in Stapleton’s runways, roadways and parking lots.

"We made a presentation going up against a multi-billion-dollar firm that could buy us out with the money in their coffee fund," quips Wachal of the nerve-wracking proposal stage. "They had a nifty PowerPoint presentation; we had some transparencies on an overhead projector, and unfortunately the bulb burned out on the projector."

But David won out over Goliath, with the RMC proposal being accepted. Now, the company was committed to a six-year demolition project with a 10-year marketing timeframe, as well as committed to finding a home for 6 million tons of recycled concrete and asphalt.

"We had a public persona of confidence, but, sure, we lost some sleep over committing to finding end markets for 6 million tons of material," says Wachal.

The company helped itself out, says Wachal, by being very careful in negotiating the terms of its contract. "It was important to have clearly defined contracts, due to changing administrations and staffs within the City of Denver," he notes.

Despite the contract caution, RMC has assumed a significant risk with its arrangement. "We were the only company who said we view the concrete and asphalt as resources," says Givan. "We aren’t charging the city to remove the material, but we needed to have the time and the space to produce and market the materials."


The redevelopment of the former Stapleton land has been a playground for urban planners, who seldom have a seven-square mile parcel of land within a major city to redevelop.

Foundation leaders and lead developer Forest City Enterprises, Cleveland, eventually sculpted a master plan for a community simply called Stapleton, with a mixed use of housing, retail, recreation and office space plotted out.

But before the new homes and shops could go up, work would have to start on removing the runways, taxiways and roads of the former airport. Recycled Materials Co. moved in with an arsenal of equipment that has been moved to the site of the Stapleton urban quarry.

The company is now in its third year of tearing up runways (which in some places have layers of concrete and asphalt up to four feet deep), transporting material to on-site and off-site crushing plants, and selling and stockpiling the material.

At the runway sites, large Caterpillar loaders with 12-yard buckets scoop up chunks of runway into 26-ton trailer trucks that spend their days dedicated to moving the runway material to recycling plants.

Before the runway is scooped up, it is broken with a guillotine or gate breaker made by Walker Equipment Mfg., Moriarty, N.M. The device is capable of cracking all the way through the paved taxiway and runway layers, which usually range anywhere from 12- to 36-inches deep, according to RMC project superintendent Myron Saylor.

Shallower surfaces, such as parking lots and roadways, are broken up with a roll-behind rotary impactor made by Impact Roller Technologies, Omaha, Neb.

The asphalt or concrete rubble can be destined for one of several crushing plants that handle the several thousand tons of material generated daily at the Stapleton site.

Two of those plants are on site at Stapleton, while five RMC mobile plants can be located at various sites, including at a nearby landfill and across town at an RMC property in Arvada.

One of the on-site plants features a large Nordberg (now known as Metso) jaw crusher that serves as the first step in creating a 12-1/2-inch minus product that is being stockpiled for a nearby federal government facility involved in a land remediation effort. This large-spec material is being moved via a 1,300-foot conveyor system that stockpiles it on the edge of the Stapleton property.

While this product is one important end market, the other materials created during the recycling process are also sorted, washed and prepared for sale as various gravel or sand grades of material. Virtually nothing is wasted.

After large chunks of runway leave the jaw plant, a magnet pulls out re-enforcing steel for the scrap market, the government-spec material heads down its long conveyor path, and smaller concrete pieces are screened into 2-1/2-inch minus and 3/8-inch sand and gravel grades.

The end result of material passing through the crusher, a trommel, several screens and (in some cases) a wash plant is seven grades of saleable material, plus the scrap steel.

According to RMC plant superintendent Jack Heard, the thick runway concrete has been an ideal feedstock for the 12-1/2-inch minus material desired by the government end user. "I don’t think we could make this material out of highway concrete—it’s not as thick," he notes.

The material stream is also clean, although one contaminant that has to be watched for is the fiber PetroMat moisture barrier that is often installed beneath runway surfaces. The company has used both manual pickers and air jets to remove fiber from the stream.

The other on-site plant includes a HazMag primary impactor that processes concrete rubble initially, before sending material on one of several paths that may involve a secondary impactor and a series of screens.

Among the key products made at this plant are roadbase materials and a Spec #57 coarse aggregate. Smaller materials are sent to a wash plant where sand and #8 gravel grades are produced.

A key off-site plant has been sited at the Denver Arapahoe Disposal Site (DADS) landfill run by Waste Management Inc. Recycled Materials Co. has sub-leased land at the site and placed a scale house to accept both material generated at Stapleton and brought in by customers who generate concrete and asphalt at construction and demolition sites. (Washout material from ready-mix contractors is also accepted at the site.)

Material is processed periodically by one of RMC’s five mobile Hartl processing plants. One of the Hartl plants is often kept busy in Arvada (which is located about 15 miles from the Stapleton neighborhood). The RMC facility in Arvada features a mobile Hartl plant on tracks, which is operated by remote control, producing a specification concrete road base product and screened rock that is used in both municipal and private markets.


The array of plants and equipment that RMC deploys in and around Denver can only remain in service as long as there are end markets for material.

One of the keys to RMC’s success has been the tireless efforts of Mark Wachal to preach, lobby and cajole for the cause of recycled aggregates.

Ken Buesing and Wachal started RMC in 1987, entering the business with a background in grading, paving and rock crushing. From the beginning, Wachal says his focus was on "value engineering—using waste to make products for on site or to sell off site."

Wachal has become a leading advocate for the production and marketing of high-quality secondary aggregates. "As a company, we object to giving recycled products a lesser standard to meet," he remarks. "It can meet the highest standards."

Building product acceptance has become a vital part of RMC’s business plan and Wachal’s role in the company and the industry. "We are dedicated to the belief that you never make a product you have to apologize for," he says. "A lot of people are looking for reasons for us to fail; they have the mindset that, ‘It’s recycled, it’s second rate.’ But we have disarmed some of the naysayers by meeting and exceeding the quality expectations of our customers."

The keys to building market acceptance include careful operations practices, making sure transportation agency specs include recycled aggregates as an option and consistently knocking on contractor and engineering firm doors and letting them know the material is available. (See sidebar)

But lobbying on behalf of recycled materials and commissioning studies is only the first part of the acceptance process. It is then up to the company to make products that are consistent and clean enough to keep customers happy. "There is a psychological objection contractors have to seeing a piece of metal, wood or plastic in a pile of aggregate. A piece of plastic can be just 1/200th of a percent of a load—well within the material spec—but it’s visibility within a pile can turn a customer off. It’s our job to keep that plastic out of there," says Wachal.


A Legitimate Effort

Mark Wachal, president of Recycled Materials Co. (RMC), Arvada, Colo., does not tolerate closed doors for recycled aggregates.

Wachal has been aggressive in pushing for the acceptance of recycled concrete and asphalt as a paving material aggregate, and he has spent his time, energy and money to make sure that the state of Colorado has not put up barriers to the use of the material.

Through his involvement with the Colorado Contractors Association Inc. (CCA), Englewood, Colo., Wachal has made friends with the contractor community that is the ultimate customer for secondary aggregates.

Wachal is currently chairman of the CCA, which is the state chapter of the Associated General Contractors of America. During his several years of involvement with the group, he has been able to vouch for the quality and legitimacy of secondary aggregates and to help ensure that RMC does not portray an image of a fly-by-night company that is desperately trying to find a destination for its products.

To help overcome technical objections, Wachal has worked with the Colorado School of Mines, Golden, Colo., to provide the data to contractors that recycled aggregates could be made with the surface qualities and the consistency they need. “Their researchers couldn’t find a reason why recycled materials are considered inferior,” says RMC general manager Rick Givan. “In fact, in many applications they are superior due to their residual cementitious content.”

Wachal’s efforts have helped make Colorado a model state in terms of its acceptance of recycled aggregates within paving materials. “If all 50 states had someone like Mark Wachal producing and then lobbying for high-quality secondary aggregates, our industry would benefit tremendously,” says William Turley, executive director of the Construction Materials Recycling Association, Lisle, Ill.

While Wachal cannot be cloned and sent to each state, his work provides a model for other recyclers to follow.

 The massive volume of the Stapleton project has tested RMC’s ability to meet its quality standards and to find sufficient end markets.

Without wanting to sound too optimistic (a sure way to jinx something that is running smoothly), Givan is pleased with the end market arrangements that have been made for the projected 6 million tons of material at Stapleton.

The need for the 12-1/2-inch minus material at the federal government site has been one key end market component. The runway-derived product has proven ideal for the civil engineering application, and RMC and the federal government were able to negotiate a contract that provides a profit margin for the company.

The company has also worked with a major aggregates producer that is using recycled asphalt and concrete as part of its material blend in both asphalt and ready-mix concrete paving materials.

And finally, the nature of the project has allowed RMC to work on site with a range of contractors, sub-contractors and developers to provide material as it is needed in the redevelopment of Stapleton Airport’s land into residential neighborhoods, commercial shopping centers, a golf course and other uses.

"We’re very pleased with our relationship with the lead developer, Forest City Enterprises of Cleveland," says Givan. "They have really been supportive in urging the use of our materials by other developers and contractors involved in the redevelopment."


It seems hard to fathom, but RMC may be past the mid-way point in terms of removing and crushing Stapleton’s runways.

The company is certainly at a point where it has to consider its future beyond the Stapleton project. "We have experienced tremendous personal satisfaction in making materials that have met or exceeded specs and been accepted by end users," says Givan. "It’s going to be unfortunate when we run out of materials. Our customer base will miss the material."

Can the project be duplicated elsewhere? "The concept of an urban quarry has proven successful," says Givan. "We think it sets the tone for large urban projects from here on out."

While projects that can yield 1.3 million tons of concrete and asphalt in one year (that was Stapleton’s 2001 yield) are rare, RMC is keeping tabs on major projects that could allow them to stay in the urban quarrying business.

The author is editor of C&D Recycler and can be contacted via e-mail at