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Simply
by changing their perspective, resourceful grading and excavating
contractors are finding attractive, profitable opportunities where
others find only a costly solid waste disposal problem. By Greg Northcutt |
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Picture this: a jumble of downed trees, stumps, and brush scattered about a freshly cleared construction site. Or perhaps, twisted, tangled strands of rebar poking through piles of concrete rubble in the demolished remains of a hotel or a factory. Then again, maybe it’s chunks of asphalt ripped up from a former parking lot. What do you see? Is it red, as in frustration and exasperation at the waste of money to dispose of this rubble? Or do you see green, as in a resource you can use to boost profits by reducing landfill fees, transportation expenses, and the cost of new construction materials while helping to reduce environmental impacts? If you’re similar to Lester Hamlin, a Nokomis, IL, excavating contractor, you see the potential for gain, not loss. He uses old concrete salvaged from sidewalks, footings, and even the floors of hog pens to build flow structures that stop head cutting of gullies in farm fields. In the process, he not only helps farmers save their soil, but he also gives them a much less expensive alternative to building poured-concrete or concrete block-lined water chutes and aprons. In addition, he saves himself the time, expense, and bother of hauling and paying to dump the debris at a landfill. "I’m bringing old concrete back to a new and useful life," he says. "It’s a win-win deal for my customers and me."
On a far larger scale, Mark Wachal, president of Recycled Materials Company in Arvada, CO, is one-third of the way through a six-year project to give new life to 6 million tons of aggregate, now in such forms as 12- to 30-in.-thick reinforced concrete runways and lighter-duty asphalt taxiways, which his company is removing from the abandoned Stapleton Airport in Denver. The resulting products, which equal or exceed the quality of virgin aggregate mixes for pavement aggregates or base courses, are being used to pave hiking trails, parking lots, and freeways. Wachal’s approach to the grading business is to make the most of what’s already available on-site. "We don’t look at a grading job unless it includes material like rock or demolition debris that we can recycle," he says. Rock and rocklike solids aren’t the only onsite materials being revamped and reshaped for a second life in new construction projects. Private contractors and engineering firms, as well as highway departments, are using woody materials–from wood and bark chips to tree trunks and stumps–to lower erosion and sediment control costs. Instead of burying profits in a landfill, they’re putting them in the bank. Here’s a closer look at how they’re doing it. Poking Trees Back Into the Ground to Protect Streambanks In the right hands, green resources can offer grading and excavating contractors a variety of recycling opportunities. Just ask David Cantrell, a past president and current chairman of the board for Land Improvement Contractors of America. His firm, Cantrell Construction company in Brevard, NC, has been preparing residential development sites and building dams for 25 years. Four years ago he used his thumb-equipped excavator to push tree root wads into streambanks to control erosion for the first time. He’s since installed seven other similar projects. Trees are an abundant resource in this area of the Blue Ridge Mountains. But suitable demolition landfills for disposing of them are scarce. Also, burning them isn’t a good disposal option because of the fire hazard to the numerous woodlands. What’s more, the clay soils that stick to the roots make it difficult for stumps to burn. Using trees as a tool to control streambank erosion is a better alternative, says Cantrell, who also serves on the board of his local Soil and Water Conservation District. "I’ve always believed in conservation, and this approach offers a sensible, effective, and economical way to do that," he says. "It makes good use of what was once considered a waste product. It eliminates the need to buy bank stabilization materials, and it offers permanent erosion control." After uprooting trees, Cantrell saws them in two, leaving the bottom 10 ft. of the tree trunk, usually a 10- to 12-in.-diameter hardwood, with the roots intact. Working from the top of the streambank, he grabs the root wad with the cut end of the trunk pointing toward the bank. Then he pulls it back into the bank until only the root ball is left exposed. In doing so, he slants the trunk so it points slightly downstream. This way the root ball can deflect water flow away from the bank and toward the center of the stream, he notes. At first, Cantrell used a chainsaw to put a point on the sawed end of the trunk. No only was that difficult, but he’s since found that it isn’t necessary. The trunks insert easily into the sandy loam banks in his area, he reports. He recommends using an excavator no smaller than about 46,000 lb. Pressing the trunks into the bank minimizes any soil disturbance, which also minimizes erosion. Also, Cantrell notes, it’s faster and requires much less labor than other erosion control options, such as sloping back the banks and seeding them or armoring them with riprap or other materials. "The roots provide good fish habitat, and they trap sediment and debris carried in the stream to build up the banks where native vegetation, like willows, can take hold," he explains. "By the time the roots decay, the roots of the willows and other plants will hold the soil in place, giving the site a natural appearance. Meanwhile, the tree trunks themselves will continue to reinforce the bank for a long time." Cantrell also uses a Model 3680 Beast Grinder to shred whole trees into pieces of mulch up to about 4 in. long. That’s after he uses a stump splitter on his excavator to break up 2- to 3-ft.-diameter trunks and remove any dirt. "We used to take these trees to a landfill," he says. "Now we use a manure spreader to apply the shredded materials, which is full of sawdust fines, about 4 to 6 inches thick on the lower slopes of road embankments to control erosion." Recycling Green Resources to Control Erosion on Slopes
Cantrell’s approach to recycling woody debris as a mulch matches that of contractors in other areas of the country. For example, in the past few years, the California Department of Transportation (Caltrans) and other state DOTs have discovered the benefits of using woody plant parts and other organic materials cleared from construction sites to reduce construction costs and protect soil and water resources. Caltrans’ landscaping specifications, for example, allows compost or mulches made from recycled products, rather than those manufactured from new materials, on any areas where no herbaceous ground cover is planted. It’s part of state efforts to reduce pressure on landfill space by reducing the amount of organic materials being disposed as waste. "Chipping woody components reduces the volume of organic materials considerably," says John Haynes, landscape architect with Caltrans. "Composting cuts that volume by another 50%. Where wood vegetation has to be removed to construct a project, we are requiring it to be chipped, stockpiled, and later respread as a primary erosion control material. We’ve found that wood-chip mulch will control erosion on slopes as steep as 1.5-to-1 as long as there is no concentrated water flow onto it." When erosion control mulch is used, no other seed or plants are usually applied for erosion control. "In areas where chipped material has been placed, we’ve noticed that rodents and birds have hidden nuts, acorns, and seed in the winter as a future food cache," Haynes observes. "Every one of those which they don’t uncover later gives us a free plant. "Usually when a landscape is installed, the existing vegetative cover is removed. Generally, the removal costs more than to put it there in the first place. The costs of using wood-chip mulch to control erosion is considerably higher ($4,000 per acre)] than the typical erosion control application of hydromulching ($1,500 per acre). But when you consider the cost of removing vegetation and applying conventional mulch, total costs for the life of the project are much less." Those aren’t the only benefits of using mulches made from green resources, Haynes notes. They control weeds and reduce the need for chemical herbicides. They also conserve water, reduce the intensity of wildfires, and provide a finished landscape appearance. A variety of commercial blowers, such as Rexius, Safety Source’s Air Belt, Shred-Vac, and Finn Corporation’s AEM Spreader, have been used on Caltrans’ projects to apply the mulch. Depending on the specific project, specifications typically call for a chip size of about 0.5 - 3.0 in. long to accommodate the pneumatic application equipment. "These blowers are equipped with hoses to spread the mulch where there is no vehicle access," Haynes says. "Some can move up to 60 cubic yards per hour through as much as 300 feet of hose. That volume is reduced to spread a thinner cover because the operator can’t move the end of the hose fast enough to spread more material." He reports that Caltrans’ use of chipped tree wood and bark has increased from 10,000 yd.3 in 1995 to more than 1 million yd.3 last year. As the availability of this material has increased, cost has dropped from about $20-$25/yd.3 to the $3-$5/yd.3 range. Using Downed Timber to Keep Soil on Slopes Several years ago, Thiess Pty. Ltd., an Australian contractor based in Sydney, New South Wales, used windrowed timber to keep sediment from washing down steep slopes on a large highway construction project. The two-and-a-half-year job, completed in late 1999, involved building a new four-lane section of the Pacific Highway on the country’s southeast coast. With production rates of 25,000- to 40,000-yd.3 per shift, the company moved 6.2 million yd.3 of earth in the 14-mi.-long project. The very steep mountainous terrain required cut slopes of 120 ft. or higher and fill slopes as high as 75 ft. Extremely high rainfall in the area added to the challenge of controlling erosion and the resulting sediment. In the forested southern half of the project, thousands of trees, unsuitable for commercial use, were cleared from the numerous steep slopes. This left the slopes vulnerable to heavy soil losses from stormwater runoff. The expected heavy sediment loads and very high and costly maintenance requirements ruled out the use of traditional silt fence to control the sediment. Also, the steep topography left little room to build basins to collect sediment. So the project’s soil conservation consultant, Toepfers Rehabilitation, Environmental & Ecological Services Pty. Ltd. of Wyee, NSW, recommend a different approach: Use the downed trees to build barriers on the slope contours. This would slow runoff to reduce its erosive force. Also, it would trap sediment to reduce pollution of streams and lakes. "This enabled us to kill two birds with one stone," explains engineer David Bax, technical services manager for the company. "It gave us a cost-effective way to control sediment, and it allowed us to make good use of all that timber. The windrows were easy to build." The trees used to construct these sedimentation windrows were 4 in. or more in circumference and with the crowns of branches intact. Bulldozers pushed trees into structures that measured no more than about 5 ft. high and 10 ft. wide. They were built no longer than about 165 ft. on the lower side of the slopes below fill embankments and in gullies. A 30-ft. gap was left between windrows on the same contour to help control any wildfires. The windrows contained no tree stumps. "These structures were extremely effective in trapping sediment, especially in the gullies," Bax says. "They collected a lot of sediment. When sediment built up high enough, we removed it and used it for fill elsewhere. By the time runoff seeped through the barrier, it was pretty well free of large sediments." Similar timber sedimentation windrows have since been successful on other highway projects in Australia, Bax reports. After completion of the project, some windrows were removed and burned for aesthetic reasons, some were left to degrade naturally, and some soon disappeared beneath fast-growing forest vegetation. Still others were pushed back into the wooded areas to provide habitat for wildlife. Using Recycled Casino Remains to Tame Stream Erosion in Las Vegas
In Las Vegas, NV, Gerry Hester, engineering construction manager for the Southern Nevada Water Authority, has been using concrete recycled from a demolished casino and other buildings, as well as rock excavated from residential development sites, to control the gradient and protect the banks of the Las Vegas Wash. This stream is subject to very heavy flows from stormwater runoff in this rapidly growing metropolitan area. "Recycling offers property developers a low-cost way to dispose of construction debris, and it allows us to build structures at less expense than using quarry rock riprap," he says. "We’re paying about $14 per cubic yard to haul and process the material as opposed to $20 to $22 per cubic yard to truck in rock riprap." Hester uses standard weight–about 150 lb./ft.3–concrete with rebar. That includes rubble from columns, beams, and walls of buildings as well as parking lots, highways, and jersey barriers. "We won’t use lightweight concrete from parking-garage floors or the floors in high-rise buildings, for example," he says. "It tends to float and roll in steam channels. Also, we avoid any concrete contaminated with lots of oils and grease, like you find on parking lot surfaces." The concrete is hauled to a storage area where a trackhoe uses a hydraulic ram to break it down to the desired size, say 30-in. D50, and shape. Rebar is cut back at least to the surface of the debris to minimize any rusting in the wash. In several cases, the concrete rubble and rock have been used in place of concrete or gabions to build weirs that slow water velocity to control downcutting of the wash channel. "Unlike a poured concrete or confined structure, the weirs built with the recycled materials can be easily modified to meet changing hydraulic conditions as discharges into the wash increase with the area’s expanding population," Hester says. "Also, it’s difficult to get down to solid rock, which is 30 to 40 feet below the channel in the wash. The recycled materials allow us to build weirs that will flex with possible changes in the profile of the wash bottom. Another nice feature is that we can fill the voids with soil to grow vegetation. This vegetation gives the weirs a more natural look, and the root systems help lock the rubble together." These structures stretch across the 500- to 600-ft. width of the wash and measure about 150 ft. from the upstream to the downstream side and about 8-18 ft. high. They’re designed to handle daily water flows of 350 cfs, a 100-year flow event of 16,000 cfs, and a 500-year flow event of 25,000 cfs. The recycled concrete and rock has also been placed in windrows at a few locations along the wash at the bottom of streambanks to protect against lateral erosion of the washbanks. Typically 6-8 ft. high with 1:1 sideslopes, these rubble windrows range in length from 1,900 to 2,500 ft. So far, says Hester, he’s satisfied with the performance of these structures. "We continue to monitor their performance and adjust our design and techniques as we place more of the recycled materials," he says. "One year ago, one of the weirs was subjected to a 4,000-cubic-foot-per-second event. There was some movement of material, but the structure held up as expected. We repaired the minor damage by simply pushing in more material." Using Concrete Debris to Limit Soil Losses on Farmland Excavating contractor Hamlin has been recycling concrete and masonry rubble from his projects for the past eight years. His sources range from sidewalks and commercial buildings in town to barns, machine sheds, and livestock pens on farms. A paved hog lot, for example, might yield six to 10 truckloads of 4-in.-thick concrete. Lately increasing demand has depleted Hamlin’s stockpile of concrete debris. He uses a wrecking ball on his trackhoe to reduce the large pieces to 6- to 8-in.-size chunks. He’s careful to avoid concrete with wood in it, and he salvages any rebar. In addition to using this concrete to build erosion control flow chutes, typically about 25 ft. wide and 30 ft. long, he recycles the material as a replacement for riprap in lining drainage channels or protecting streambanks from erosion. He’s also used it to build stream crossings for farm machinery. "If I didn’t recycle this debris, I’d be paying $36 to $38 a ton to dump it at a landfill," he says. "Customers don’t pay for the debris itself. But I do charge for transportation and handling. Usually that totals about $50. That compares to about $180 they would pay for a load of rock trucked to their site." Converting Crushed Runway Rubble to New Highway Paving Processing offers even more options for putting new life into construction site debris. Recycled Materials Company, for example, transforms concrete and asphalt pavement into materials than are both less expensive than virgin aggregates and perform just as well, if not better. Currently, Denver’s old Stapleton Airport, which is being redeveloped for residential, business, and other uses, is providing a bonanza of such resources. The company is tearing out and crushing about 975 ac. of concrete and asphalt runways in addition to building foundations and converting them into 11 different types of aggregate–from riprap and aggregate bases to various sizes and qualities for ready-mix and asphalt pavement. And that doesn’t count the rebar and other ferrous metals it is separating from the debris. Recycled Materials Company has even created a topsoil planting medium by combining fines washed from the crushed concrete with shredded branches, tree limbs, and such and then composting the mixture. "We’re trying to change the mentality around the country toward wasting recyclable resources," Wachal says. He’s been doing that ever since he started in this business 24 years ago. Wachal has also been battling against the perception that old concrete aggregates are inferior to those in new concrete. Judging by results to date, he’s been successful. Wachal reports that more than 10 million tons of his company’s recycled aggregates have been used in the Midwest and West on road and street construction projects, primarily interstate highways. In addition to recycling concrete from the Sioux City, IA, airport, the company has consulted on other recycling projects with airport officials in such areas of the world as Germany and Russia, he says. "We’ve never asked that the performance bar be lowered for our aggregate products. We only ask that recycled concrete be considered as a source of aggregates and that we be allowed to produce a product that is equal to it or better in terms of design criteria, gradations, hardness, durability, and the like," Wachal states. Because of higher Federal Aviation Administration quality requirements for the virgin aggregate used to make airplane runways and taxiways, concrete made from recycled airport concrete performs better than concrete recycled from typical street and road pavements, which often includes dirt, wood, and other debris in the rubble, he says. In fact, Wachal cites studies by the Colorado School of Mines that found that the recycled aggregate from Stapleton Airport equals or exceeds the quality of virgin mixes. This recycled aggregate costs about $1/ton more than virgin aggregate, he notes. However, because the virgin aggregate must be transported farther to Denver-area job sites and because of the higher concrete yield when using recycled aggregate, Wachal says his product is competitive in price at point of use. He points out that, on a per-unit-of-weight basis, recycled aggregate produces more concrete than the same weight of virgin aggregate. Why? Because air was entrained when the original runway concrete was made. That in turn makes the recycled aggregate lighter. Uncrushed, undisturbed quarry stone weighs about 175 lb./ft.3, he explains, while the same volume of concrete weighs about 150 lb. Consequently, a ton of recycled aggregate will produce about 10-15% more volume of concrete than a ton of virgin aggregate, he explains. Also, Wachal reports, when used as a base material, the R-value strength of recycled aggregate is often higher than virgin aggregate. "As a result of all these factors, recycled concrete is a better value at the job site," he says. Recycled asphalt also enjoys an economic advantage because as much as 30% of the highest-cost component–the liquid asphalt–is available from the original asphalt rubble, he adds. Last year, Ralph Bell, operations manager for Castle Rock Construction Company in Castle Rock, CO, used 30,000 tons of a Recycled Materials’ Stapleton Airport product as the course aggregate on 4.5 mi. of I-70 pavement east of Denver. "We tested several mix designs of the material before beginning the project and it performed really well," Bell says. "Performance on the project itself was excellent. Also, we saved $2 per ton over the $13-per-ton cost of quarry rock." He reports that his company plans to use the recycled aggregate as base courses for future concrete and asphalt paving projects. And so, more projects continue to join the ever-growing list of applications where materials, which many grading and excavating contractors have viewed as an unwanted waste, are now being seen as part of the solution to rising construction costs. It’s a trend that bodes well for the profits of contractors and project owners and the well-being of the environment. Greg Northcutt is an editorial consultant to the International Erosion Control Association and a writer on environmental issues.
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