In today’s economic environment, it is difficult to imagine how a contractor or production facility can survive without being involved, to some degree, with the recycling of concrete, asphalt and demolition materials.
This demand has added new operational issues that must be properly managed with the rest of their business. While most contractors and producers understand the importance and need for recycling, many are still unsure of which options are best for them, what equipment should be utilized, and how much of that responsibility they should handle themselves.
A Brief History
Concrete, asphalt and demolition material recycling got its start in the 1970s, when contractors and producers (asphalt, concrete ready-mix, etc.) first started recognizing the value of these renewable resources. Early on, many turned to outside contractors to crush and screen their recyclables, as most facilities didn’t fully understand how to properly process this material, and the necessary equipment for the job was expensive and limited.
But over the next 30 years, recycling equipment and processing plants became increasingly sophisticated, offering a variety of product and layout choices from jaw and impact crushers to vibrating screens, to complex multi-circuit systems. And with the recent development of new highly-portable crushing and screening systems, user-friendly controls and designs, and low-cost operation and maintenance, many contractors and producers are now benefiting from owning their own recycling systems. Today, with the proper equipment and process, the average cost savings can be as much as $2 to $3 per ton versus outsourcing.
The Benefits of Recycling
Recycling can benefit an operation in several ways. A demolition contractor, for example, might reduce or avoid landfill and transportation costs altogether by crushing on site. A grading or site-prep contractor can recycle common site material for use as base or erosion stone, and avoid the cost of its removal and the need to purchase new crushed rock.
Producers might generate a new revenue stream by recycling their by-products that would otherwise be considered waste. All these benefits can result in a more efficient, and ultimately more profitable, operation. Depending on project size, recycling investments can be recovered after as little as one or two projects, or a season or two of operation.
Portable Recycling Plants
Determining which recycling plant is best for an operation requires a proper review of needs. Annual tonnage requirements, material type, end-product and site location are all important considerations when making an equipment investment.
A key decision that impacts most of these issues is chassis type, and recent product advancements have changed the approach many now follow. Although stationary systems led the industry early on, most contractors and producers will benefit more from the flexibility offered by today’s portable recycling equipment.
Configured as either wheel or track-mount designs, portable plants can deliver the same effectiveness and productivity as their stationary counterparts, but with the added benefit of easy relocation. Even when a stationary machine is required, a moveable skid-type plant still provides some additional degree of flexibility should it be necessary to relocate the system.
For rates of 100 to 400 tons per hour, a track-mounted crusher or screen is most appropriate. Moved to a job site by lowboy trailer, the self-propelled track-mount system can drive itself to the operating location and be ready to operate. This fast set-up makes it economically feasible to move for even small jobs in the 10,000-ton range.
Because of this mobility, a track-mounted system can move through a job site to the feed stockpile, rather than moving the feed material to the unit. In addition, because the unit can be controlled remotely, less labor is typically required.
A small to medium-sized wheel-mounted unit also can produce work in this volume range, but will likely not be able to perform with equal efficiency. Overall, track-mounted systems provide a low-profile, quick set-up, cost-effective solution for efficiently managing smaller recycling jobs profitably.
For higher-volume capacity, large wheel-mounted crushers and screens should be used. Pulled to a job site by tractor truck, wheel-mount systems must be maneuvered into place upon arrival.
Set-up time can range from hours to days, and once set, they cannot be quickly relocated around the site. Although these systems require a larger commitment and cost to operate, their production rate of 500 tons per hour or higher can be very effective for recycling projects of 100,000 tons or more.
Crusher and Screen Options
After determining the most appropriate chassis configuration for the application, the crusher and screen type must then be decided. Two of the most common types of crushers used in recycling are jaw and impact crushers, although cone crushers play an important role as well.
Jaw crushers are compression crushers designed for primary reduction of large-size feed materials, such as concrete chunks. A typical large portable jaw crusher has a feed opening of 26 by 50 in. and is track-mounted; even larger jaw crushers are available on wheel-mounted chassis. With their adjustable jaw setting, they can produce products up to 10 in., or with a tighter adjustment, produce products down to 3 in.
Sometimes, a jaw crusher is followed by a secondary crushing unit and a vibrating screen, for the production of one or more smaller final products. Jaw crushers are suitable for processing concrete, stone and demolition material such as brick and block, but are not well-suited for crushing asphalt.
Another popular crusher style is the horizontal shaft impact crusher. As the name implies, impact crushers process via impaction, and can be employed as a primary or secondary unit in recycling applications. When compared to jaw crushers, impact crushers produce smaller product sizes, and often at higher tonnage rates.
They do have higher wear costs, typically ranging from 15 to 25 cents per ton versus 10 cents per ton for a jaw crusher. However, impact crushers provide tremendous versatility, effectively processing concrete, limestone, asphalt and most typical demolition materials; impact crushers are not designed to process harder, granite-type stone.
A large, portable track-mounted impact crusher will generally accept a feed size up to 30 by 30 in. with a thickness of 12 in., depending on the crusher size, but to maximize their performance, feed material should be prepped to an average size of 20 by 20 in. Horizontal shaft impact crushers typically produce an end product of minus 1.5 by zero in., but the aprons can be adjusted to generate a slighter coarser material up to 5 by zero in.
Where necessary, cone crushers also can be employed in a recycling system. Designed as secondary or even tertiary units, cone crushers operate by compression, and can effectively process a screened 5-in. feed to a [final product of minus 1 in.
Cone crushers are suitable for crushing concrete, stone and demolition brick and block, but are not recommended for processing asphalt. As with jaw crushers, cone crushers also typically experience wear costs of 10 cents per ton.
Finally, the vibrating screen concludes the process by separating the crushed material into [final spec products. Available as single, double and triple-deck (and sometimes quad-deck) models, a vibrating screen is capable of producing multiple end-product streams. Vibrating screens also are available in horizontal or inclined configuration. Horizontal screens provide lower head room, higher screening G-force and greater adjustability. Inclined screens tend to provide greater throughput and capacity, as gravity assists the movement of material across the surface.
Some impact crushers also are designed with on-board vibrating screens, providing crushing and screening capability in closed-circuit configuration on a single chassis. Requiring far less space than a two-chassis plant, they are able to produce a final spec product from feed material in one continuous processing flow.
Regardless of which recycling plant is ultimately employed, an efficient and cost-effective process can be maintained if some general guidelines are followed. Properly prepped material will ensure the most productive crushing process by eliminating bridging; numerous muncher and shear attachments are available to ensure that feed material is well prepped.
The removal of excess re-bar and steel, as well as wood and other non-concrete material, will eliminate the potential for costly plant damage. While a good recycling plant is designed with a higher threshold for contaminants, extra care prior to feeding will ultimately result in a more productive system.
Also, because most recycled feed material contains steel contamination, it is important to have one or more good, well-placed magnets on the plant to remove steel waste from the finished product.
Often, dust-suppression systems are required on recycling plants as some materials, such as concrete, can create a great amount of airborne dust. When stockpiling the finished product, radial stacker belt conveyors are much more efficient than a front-end loader. To accurately track production, a belt scale can be mounted on the radial stacker conveyor to measure discharged material.
Finally, never undersize a vibrating screen. Undersized screens will not produce a clean spec product when running close to capacity, and can significantly slow down production flow. Maintaining maximum performance from a crusher requires the vibrating screen to perform at equal levels.
After carefully considering the available options, and determining the proper system and configuration, choosing an equipment manufacturer is the final step. After making all the correct decisions and planning for the most appropriate plant, investing in a system manufacturer that fails to provide adequate service and support will reduce the effectiveness of the operation in the long run.
It is obvious that reliability and performance are critical in any equipment investment, but equally important are the service, parts availability, training and overall support provided after that equipment is installed.
Look for a domestic manufacturer that incorporates design, engineering, fabrication, service and support in their own factory; suppliers that outsource any of these processes, or off-shore manufacturers without local representation, may not be able to deliver complete or timely after-sale support. Thoroughly research and understand the entire manufacturing process to ensure the system maintains its investment value long after the initial delivery and installation.
Clearly, the recycling of concrete, asphalt and demolition materials has become a more mature and advanced industry. Contractors and producers have an enormous variety of systems, plants and attachments available to serve their individual application.
With thorough analysis of the operation, and proper due diligence in selecting an equipment manufacturer, every facility can reap the benefits of material recycling, and participate in this cost-saving and environmentally responsible practice.
(This story appears courtesy of Kolberg-Pioneer Inc.)