Rick Givan, director of special projects for LVI Environmental Services Inc., headquartered in New York City, shakes his head when he sees someone trying to set up a plant at the edge of a job site, or worse at a separate location. When processing reinforced concrete, overlooking details such as handling distance or overfeeding the hopper can reduce the potential value of a job, Givan says.
Another mistake operators make all too often, according to Dan Jere, a product support specialist at Carroll, Ohio-based Company Wrench, is failing to process concrete down in size sufficiently. He also says operators often “put large pieces of concrete into the crusher that have large amounts of steel in them.” Too much steel will wear down the blow bars and cut holes into the conveyor belts.
Givan, Jere and other industry experts provide the following five tips for crushing reinforced concrete.
1. Choose the right equipment
“You must have the right equipment for the job,” Jere says. ”You will never want to have a piece of equipment that is either too big or too small. So if you’re processing concrete footers that are 6 feet thick, a concrete pulverizer or a universal processor will not be the best tool.” He continues, “What would work best is a hydraulic hammer that can fracture the concrete into manageable pieces that can then be processed.” These more manageable pieces can then be processed with a concrete pulverizer or universal processor to remove rebar, he adds.
Ron Griess, crushing and tracks product manager for KPI-JCI, Yankton, S.D., gives another example of why equipment selection is imperative. “If the concrete is heavily reinforced with rebar, it is common and recommended to use a backhoe with a shear attachment to break or shear any excessive rebar from the broken concrete. The shorter the rebar is, the less likely it is to get hung up in the machinery, and the easier it is to be extracted by the magnet.”
Magnets on skid loaders can be used to sort the feed pile so the magnet can pick up rebar pieces for the shearing process. This takes some of the load off the magnet on the crusher, Griess says.
2. Reduce Handling
Givan emphasizes the importance of knowing exactly how a job site is laid out. “Always sketch a job site and find the best ways to reduce handling,” he advises. This will help keep the plant close to the actual pile of reinforced concrete. “Ideally, you want to move the plant closer and closer as the project goes on,” he says. Moving material too far will hinder the value of a job, according to Givan.
Griess also says it is best to line the largest pieces of material up first to be processed with hydraulic hammers. He suggests creating a flow so tipping vehicles can quickly be inspected, weighed and tipped without bottlenecking traffic or interrupting the crusher operation or the loader feeding the crusher. He explains, “It works in an assembly line so that the smaller pieces are fed to processors to be processed down and then fed into the crusher.”
Griess also recommends positioning the field pile adjacent to the crusher to minimize the distance and time the loader has to drive to keep the crusher fed.
3. Always pre-process
Using discretion up front will save time and money later when it comes to what types of material to accept for processing. Griess says, “The cleaner the material the more marketable and valuable it is.” He also says to pre-screen for dirt and mud to avoid build-up from clogging the hoppers, chutes or the inside of a crusher.
D.J. Cavaliere, operations manager of Cavaliere Onsite Recycling/Rubble Master, Stamford, Conn. suggests cutting and removing any extruding rebar longer than five feet from the chunks of concrete. “The longer rebar has a chance of tearing conveyor belts,” he says. “This is especially critical when crushing with a jaw crusher. I also like to have any lump pre-broken to a 20-inch minus size to reduce the risk of solid base plates from foundation piers entering the crushing chamber. These are normally embedded in concrete.”
Gerry Mangrich of McLanahan Corp. (formerly Universal Engineering), Hollidaysburg, Pa., says pre-processing depends on the type of crusher. “Typically, slabby material should be pre-broken or sheared into manageable pieces to minimize the occasional bridging in the hopper ahead of the crusher. Ideally, exposed reinforcing rod should be trimmed to reduce the potential for snagging and jamming through the transitions,” he says.
“Whether a contractor is using a jaw crusher or an impact crusher as a primary crusher, most crushers are designed with a reasonable level of forgiveness,” Mangrich says. Even so, he also advises checking demolition rubble for the floor safe and manhole covers.
4. Magnet configuration
If metal must be separated from the concrete after the material has been crushed, then magnet configuration is an important consideration to ensure maximum extrusion. Many operators and equipment manufacturers agree an overhead belt magnet is best for the job.
An overhead belt magnet should be installed over the end or beside a discharge conveyor and after the primary crusher. Mangrich adds that once the ceramic core on a magnet is damaged, the magnetic field is destroyed. An overhead belt, he says, can help prevent repeated impact.
5. Adjust when necessary
Adjustments may need to be made to a crusher for it to handle concrete that contains steel reinforced bar. Cavaliere says he recommends the crushing gap be set to at least double the diameter of the largest piece of steel rebar that may enter the crushing chamber.
“I also notice that operators often tend to load the crusher with an excavator that is too large or have a bucket that may be too large,” he adds. “For example, if your crusher will have an opening that will only allow a 36-inch wide chunk, then you should feed with a 30-inch to 36-inch bucket. This is an easy gauge for an operator.”
If larger rebar is in the concrete and cannot be removed from the concrete, the crusher should be opened up to allow larger material to pass through. This helps remove the steel from the crushed material on the discharge belt, according to Griess. “Jaw crushers work best for large amounts of steel in the concrete,” he adds.
The author is assistant editor of Construction & Demolition Recycling and can be reached at firstname.lastname@example.org.