Application Tips: Drop hammers

Since drop hammers primarily use the laws of gravity, rather than hydraulics, to perform their work, their only mission is breaking up concrete on a flat plane.

But they excel in this application to the point you might want to have one in addition to your hydraulic breakers. With its blunt breaking head, a drop hammer can stay on top of the material to be broken, shattering it, as opposed to creating a hole like a hydraulic breaker.

When attached to similar-size carriers, drop hammer attachments can break 8- to 10-inch concrete faster than hydraulic breakers, says Justin Odegaard, attachments product representative for Bobcat. That’s because drop hammers produce long-running cracks fanning out in all directions from the impact point, he explains. “With a hydraulic breaker, you break smaller sections at a time,” Odegaard says. “In horizontal applications, the productivity gains you can get from a drop hammer are tremendous.”

Another reason drop hammers tend to work faster than traditional breakers, especially when mounted to compact carriers, is that a breaker often can’t draw enough power from a small carrier’s hydraulic system to match the impact force created by the massive weight of the drop hammer.

On single-pour slabs, a drop hammer will break concrete all the way through – even though the surface remains level and the carrier machine can continue operating on it. Odegaard says contractors using drop hammers for the first time are often concerned because the concrete doesn’t look like it’s broken up much. But when they begin picking up the pieces they find the underside of the concrete is more fractured than the top layer. “High production will occur when the operator recognizes he may not have to impact the concrete in such close patterns,” says Frank Smith, president of Universal Impact Technologies.

Since drop hammers are quieter than conventional hammers and breakers, they could be a solution for your noise-sensitive jobsites. “The drop hammer just makes a soft thud when it hits,” Odegaard says, compared to the loud, rattling sound of a hydraulic breaker. And because most breakage occurs underneath the surface, drop hammers create a lot less dust than a breaker.

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The concrete, rather than your carrier machine and operator, absorbs most of the impact force of the drop hammer, making it more pleasant for your employees to use than a hydraulic breaker and causing less wear and tear to your machine. “Drop hammers will dissipate the shock back into the ground as long as the operator keeps the breaker in contact with the ground,” Smith says.

Along with these advantages, however, come several drawbacks. The material you’re breaking must have some horizontal room in which to move or it won’t crack effectively. For this reason, hydraulic hammers and breakers are better in trench-work applications, Smith says.

While the lengthy cracks a drop hammer produces are a good thing if you are demolishing an entire concrete pad or structure, they can cause serious problems if you are trying to contain the destruction. With a hydraulic breaker, you can use chisels to help you control where the concrete breaks. There’s no way to control the cracks a drop hammer triggers.

And because a drop hammer hits with impact energy much greater than that of a hydraulic breaker attachment, its shock loads travel through concrete farther. These shock loads could make parking decks – often demolished from the top down – unstable. Or, if you’re demolishing only part of a structure, they could cause unwanted damage to the remaining portion.

Before you buy
Know the average thickness of the concrete or asphalt surfaces you plan to break. A hammer that’s too large will be ineffective because it will punch through thin material rather than cracking it, Smith says. On the other hand, a breaker that’s too small for the application will not crack the material, resulting in unsatisfactory production.

For 3- to 6-inch, slab-on-grade concrete, Smith says he recommends his company’s smallest model, which provides 1,500 foot-pounds of impact energy per blow. He advises customers to use a 3,500-foot-pound model for 6- to 14-inch concrete and a 9,000-foot-pound model for concrete slabs of 14 to 30 inches.

If the concrete has already been pulled up and broken into chunks, the thicknesses the machines are capable of breaking go up quite a bit, Smith says, because the exposed concrete has more room to move, thus enhancing the shattering effect.

Easy to operate, but not foolproof
Operating a drop hammer is relatively simple. On Bobcat’s model, you activate the hydraulic motor that turns the chain, raising the hammer, and then travel around the surface. The hammer will raise and drop automatically at a rate of about 20 blows per minute. Using a hydraulic breaker, on the other hand, requires the operator to lift and reposition the tool.

Depending on how thick the concrete is, you may have to hit the same place more than once. You might also do this if you are trying to crumble the concrete into small pieces. If you are breaking up concrete reinforced with steel, for instance, you’ll need to crush the concrete into fine pieces in order to properly strip it from the rebar. Be careful, however, that you don’t hit the same spot so many times that the hammer has nothing to contact when it falls, Odegaard warns. If this happens, the weight will hit the bottom of the drop hammer’s frame, effectively trying to break itself. Eventually it will succeed.

You’ll need to take into account how you’re going to dispose of the concrete when deciding on the size of the broken pieces. Some states regulate the size of such material, and many disposal sites set such limits as well. “As an example, some sites will only accept fairly small pieces [with dimensions of less than 18 inches] and do not allow any steel to be in that concrete, while other sites may take anything, whether it has steel or not, and will charge the contractor accordingly,” Smith says. “He will charge more for the larger pieces because it costs him more to break these pieces down to the end product he is producing.”

Guard against flying concrete chips
As with any application that involves the potential for flying debris, proper safety gear including a hardhat and eye protection should be worn by the operator and anyone else in the area where the drop hammer is being used. Do not operate a drop hammer if another person is within 10 feet of the carrier machine and keep the cab doors and windows closed, says Al Springer, national sales manager for Allied Construction Products. He also recommends window bars or screens to protect the machine’s windows from flying chips of concrete.

Make sure you use the drop hammer’s locking mechanism to keep the weight in place when you transport the tool. The lock will allow the weight to travel only 1 or 2 inches, preventing it from sliding out of the frame.

Another option
A third choice for getting rid of concrete is a product powered by a giant compression spring. Like a drop hammer, the Allied Hammerhead II slab buster doesn’t use hydraulics to accomplish its chief task, and like a hydraulic breaker, it can be used to demolish vertical surfaces such as walls. The slab buster’s impact produces an effect similar to that of a drop hammer.

“They both ‘rubble-ize’ concrete, making it easy to remove and load for hauling away,” says Al Springer, national sales manager for Allied Construction Products.

Hydraulic breakers will outperform slab busters, however, in demolishing very thick concrete such as bridge abutments and large concrete footers, he says. High-reach concrete demolition is also best left to hydraulic breakers.

When operating a slab buster, resist the urge to slam the attachment onto the material you’re trying to break. “The operator should let the machine slide from position to position,” Springer says. “No down pressure is required. Slamming it down on the concrete does not make it hit any harder.”