Let’s face it, concrete will crack and fail. Martin Applebaum, a general manager at Driveway Maintenance Inc., headquartered in Miami, presented at a property management companies meeting one evening in Southwest Florida, explaining to those attending that concrete is going to fail. “The purpose of the welded wire mesh is to hold the concrete when it cracks,” he told us. Applebaum even proclaimed the purpose of the joints in concrete sidewalks and pavements is to interrupt the cracking. “The reason that you cut joints in concrete pavements is because it wants to crack,” he said. “The joints are structural designs. It’s a control joint….You get corner breaks because joints are the weakest point of the concrete pavement.”
Once the concrete sidewalk or parking lot starts to crack, the property owner has a safety hazard and/or vehicle maintenance nightmare on his hands. Then your client needs it fixed. Depending on the application, you may find rebar within a slab. You may need to scarify a mere half-inch along a roadway to prepare the surface for tack and blacktopping, or you may need to break out failed Portland concrete cement (PCC) all the way to the dirt.
Whatever your call to duty, consultant John Ball reminds you to start with a plan before you cut. He’s the proprietor of Top Quality Paving and Training, Manchester, New Hampshire, and he said the first step to removing concrete is calling Dig Safe. Even though you’re not technically digging holes, you need to know what’s under the pavement.
For example, the local news was on the scene when a simple mill and fill job on Kapahulu Avenue in Honolulu in June of 2015 turned catastrophic. The milling machine ruptured a gas line that lay about 8 inches below the pavement instead of the required 3 feet. The result was an explosion, a long-burning fire, two injured workers and thousands upon thousands of dollars of damage.
For city projects, the utility company may not be able to offer you a precise depth of pipes, cables or lines, but the demarcation service is intended to increase worker safety. Ball said to consider also the damage a drop hammer or cutting saw could do to fiber optic cable, which costs about $80,000 per foot to replace. I’m no bean-counter, but I can tell you destroying that kind of utility would eat into the project’s profit margin. Take the time to get utilities marked before you crack and dig up concrete slabs, for safety’s sake.
Assess the project in front of you, and the utilities in its immediate vicinity, to select the right removal technique and equipment. Know what the machines in your fleet are capable of—and what their limitations are.
For example, if you get the job to remove and replace a 200-square-foot loading zone that comprises 6 inches of concrete throughout, you’ll be hard-pressed to retain your laborers or make any kind of profit by going at the slab with a hand-held cut-off machine and a loader bucket to pick up pieces. Consider the customer’s reaction when you can’t get his loading zone back in readiness because you’re messing around with saws and diamond blade replacement for a few days behind his store. Sure, he should have used asphalt to begin with, but that’s another discussion altogether. Your concern is how to get rid of concrete most efficiently so you can turn a profit and make the customer happy enough to recommend you to others and call on you for future work.
Here are some of the best ways to break, mill and/or remove concrete. You can discuss these options with a project engineer/manager in your company to scope out the best way to face your next perplexing slab of gray matter.
While it’s not ideal, it is possible to mill concrete pavements to prepare the surface for asphalt overlays. Kyle Hammon at Roadtec Inc., Chattanooga, explained that this milling of concrete is typically performed to remove surface flaws. “Most of the time, concrete is milled at a shallow depth of a couple inches,” Hammon said. “It’s just to scar the surface and take a thin layer off the top to get a better bond of the surface with the thin asphalt to follow. The tack coat always performs better on a finely milled surface.”
Not every tooth—or bit—on the market is going to be ideal for chewing concrete. Of the 30 cutting teeth the company offers, Kennametal suggests only its RoadRazor II™ RZ4-01, RZ1-PT7, RZ1-PT and RZ3-PT for concrete milling. Depending on the application, Wirtgen recommends its Rhino W1-10-G/20X or W1-13-G/20X cylindrical carbide tip cutting teeth for concrete milling. Wirtgen’s Ken Snover shared that the W6M/20X can also be used in some concrete applications. Consultant Ball has seen the use of the diamond teeth over the years to get the kind of life out of bits that concrete demands.
“Carbide bits will increase the wear life,” Hammon said, “but concrete is so hard on the machine. It accelerates wear on the drum and the machine itself.”
What you’re looking at when selecting a tooth for concrete milling is a hardness based on the Rockwell scale. The folks at KutRite Manufacturing explain it simply: “The Rockwell scale is based on the indentation hardness of a material.” The harder the material is without becoming brittle—or the “more optimally” it scores on the Rockwell scale—the better its longevity during heavy-duty use.
No matter which bit your crew uses, the silica dust produced by milling a concrete pavement is not to be ignored. “It definitely generates more dust and fine particles than milling asphalt,” Hammon said. “Have the water truck nearby. Have masks on the crew.”
Once the milling is complete, be sure to clean the surface completely, as you would with an asphalt pavement. Get fine millings up as best as you can to make a clean surface for the tack to coat and the asphalt lift to adhere to.
Scarifying is not milling. When scarifying a surface, you merely scrub—or scar—the surface layer as if grating the top peel of an onion. This process is often used to remove thermoplastic, epoxy, cold plastic coatings or other markings, or to roughen the surface for a treatment to follow. Check out the pictures of the Flatliner from Keystone Engineering for an example of one such tool that is used as an attachment to scarify concrete surfaces.
Resonant rubblizing impacts the concrete surface for the purpose of breaking it. The resonant hammer(s) hit the pavement from a low amplitude at high frequency to cause the fracturing of the concrete slab without breaking all the way into the base. With some rubblizing machines, the hammers fall from a higher point, slamming the pavement with more force. Check out the two main types of resonant breaking machines in the pictures on page xx. Once the slab is fractured, its interlocking “rubble” forms the matrix of support for the overlay to come. Let’s see that in practice in the next section, the crack and seat method.
Crack and Seat It
As Darwin Larson detailed in the winter 2016 edition of the Iowa Asphalt Report, the City of Norwalk, Iowa, has adopted the use of crack and seat followed by hot-mix asphalt (HMA) overlay to lessen the cost of replacing all the PCC panels from the 1960 to 1990 time period that are now failing. Larson is a professional engineer and an Asphalt Pavement Association of Iowa (APAI) municipal field engineer who reported on the 4,000-foot-long project of Wakonda Drive from Hwy. 28 to Lakewood Drive specifically. For that job, a specialized concrete breaker fractured the existing PCC roadway into 18-inch to 36-inch panels and pieces. Next, the team drove a heavy roller over the cracked pavement to “seat” the jigsaw puzzle. Larson wrote in the Iowa Asphalt Report, “The primary purpose of this process is to reduce the amount and severity of the reflective cracking thus prolonging the life of the new HMA overlay.”
After the crack and seat process, the crew placed 8 inches of HMA, which solves the City of Norwalk’s infrastructure woes.
Companies sell or rent new and refurbished ultra high pressure water pump systems that have the force to cut through concrete while leaving the rebar within intact. The pieces of equipment—and the services—that Blasters Inc. offers are designed for industrial cleaning, concrete hydro demolition, surface preparation for repair and rehab, highway paint stripe removal, coatings removal and more. While the company was hesitant to share images in a print publication, you can check out their machines in action on their website at www.blasters.net/hydrodemolition.asp.html. Other companies that provide such technology include Hydro-Technologies Inc., Jefferson, Indiana; Midwest Mobile Waterjet, St. Paul, Minnesota; and NLB Corp., Signal Hill, California.
Saw Cut It
To this point, the methods of breaking concrete that we’ve discussed have been appropriate for roadway applications. Let’s say you have a parking lot, homeowner’s driveway, city sidewalk or other small area with failed concrete to address. You aren’t going to take a large machine with a resonant hammer between its tires to a quiet neighborhood and start pounding the ground just because the homeowner chose to use a substandard paving product. Instead, you may elect to cut out the area of concern with a cut-off machine.
Before you turn the crew loose on the job, think about safety. At the very least, cut-off machines should have a guard to protect the worker from the blade. Managers should be sure workers wear appropriate gloves, face masks, eye protection and other personal protective equipment.
Stihl now offers a machine with electronic water control for wet-cutting to reduce the dust generated near the worker. The STIHL TS 420 A (EWC) is designed to use up to 50 percent less water than conventional systems; it meters the water supply for dust suppression during operation, etc. You can even ease the strain on workers’ backs by affixing cut-off machines to walk-behind carts. Stihl provides the Cutquik® cart that’s designed to “fit” the TS 400, TS 410, TS 420, TS 700 and TS 800 machines. It offers a forward-weight orientation so the saw is positioned for work and the operator is standing behind the machine, out of harm’s way.
Break It with a Tool
After watching laborers work day in and day out in blistering heat with diamond blade cut-off machines, I can attest to the fact there are many times when the crew would be better off using either a handheld hydraulic breaker or a breaker attachment on the front of a skid steer to remove concrete slabs. There are a multitude of both on the market to choose from and manufacturers have been hard at work making them more user-friendly.
For example, the interiors of Caterpillar handheld breakers feature a tri-suspension system (on their “silenced” models) that comprises the suspension jacket, the upper buffers and the lower buffers. Having buffers at both ends of the power cell in there absorbs reflective forces. This isolates the forces from the machine, which reduces operator fatigue. The two-piece suspension jacket isolates the front head, which is how sound and vibration are reduced.
Stanley Hydraulic Tools, Milwaukee, Oregon, offers a variety of mounted breakers, including the MB05. Its skid steer bracket has four positions so you can break pavement slabs or angle it up to break a landscape feature/wall. This type of multi-position option mounting head is available with the Toro Dingo 23135 hydraulic breaker, too. It offers 180 foot-pounds of force while delivering 1,250 blows per minute.
Rich Elliott, the product manager for hydraulic attachments with Atlas Copco Construction Equipment, Commerce City, Colorado, discussed the weight demands of the tools. “For commercial-sized pavement applications, the most popular breaker attachments might be our SBU 220 and SBU 340 solid-body models,” Elliott said. “Both breakers are relatively lightweight, compact and pair well with skid steers and mini-excavators—common pieces of equipment for this sized application—because they fit a wide range of carrier weight classes….the SBU 220 and SBU 340 offer a streamlined profile, making them easy to maneuver close to obstacles.”
Keep It Clean
No matter what method your crew needs to use for the application of the day, it’s important to keep the job clean. Not only do crew members need to have their best working environment for their safety and comfort, they also need to have the project itself under control at all times. Ball reminds readers that having a clean surface will help you start and make better transitions when it comes time to pave, if that’s part of the project. The clean surface helps with adhesion of tack, patch material, sealers and pavement lifts. The clean site and surface also speaks well of your company. The traveling and shopping public sees your crew and your job. Make sure the general public sees a clean, safe, efficient crew doing a good job of removing and repairing the failed pavement.