There are lots of ways to get concrete from the ready-mix truck to exactly where you want it when placing a slab on grade, but the bottom line is you want to keep the hand work to a minimum. How you select among the available options depends on access conditions, timing considerations, and economics.
“Pumping should be the first option,” says Keith Bauer of Charlotte, N.C.-based Carolina Coastal Pumping. And for many, it is. Pumping offers speed and also keeps the weight of ready-mix trucks away from the slab base. But there are good alternatives to consider when pumping isn't practical.
According to Todd Truemper, of Tilt-Con Corp., Orlando, Fla., choosing the delivery method depends on job access and what's being embedded in the pour. Having access in and around the site, with good subgrade that will support the delivery trucks, is a key criterion.
Beyond that, what's in the floor can make discharging directly from the truck's chute difficult. “If there are a lot of block-outs, a lot of plumbing, that means you'll have to be jockeying trucks all around,” Truemper says. Tilt-Con self-performs tilt-up panel work as well as foundations and slabs on grade. This type of work frequently is supported by company-owned concrete boom pumps.
Got good subgrade?
Jeff Hamburg, president of Blair Concrete Services, Wilmington, N.C., says successful concrete delivery hinges on site logistics and pumping methods.
“Subgrade is everything,” Hamburg says. “If access permits it and the subgrade can support the weight of the ready-mix trucks, truck dumping is optimum.” However, if either poses a problem, Hamburg's next preference is to pump. With the bulk of the company's work now consisting of hospital and university buildings, most are pumped with a system, often including several hundred feet of pipe. The challenge, he says, is to have a placing crew that knows how to move the hose around to place the concrete efficiently.
On projects where a boom pump is a feasible option, the company sometimes uses one placing crew and two pumps and piping systems in a leapfrog fashion. The concept is simple: The crew places as much concrete as it can within the reach of the first pump. They continue with concrete from the second pump while a smaller crew breaks down the first line and repositions the pump. By the time the placing crew reaches the limit of the second pump, the repositioned first pump is again ready to go. “We do end up spending a little more on pumping,” Hamburg says, “but we can pour twice as fast. Also, this way we always have a built-in backup pump available.”
Overhead clearance is another important part of site access. Brothers Joe and Scott Swederski of Swederski Concrete Construction, Spring Grove, Ill., like to pump concrete when they can. But much of their work is in large warehouses that already are under cover. Even when you can get a pump truck inside, “it takes a lot of headroom to open up a pump,” says Joe Swederski. “Plus, there can be a ventilation problem in enclosed spaces.” The crew typically is already running a laser screed, and adding the exhaust from a pump truck can require additional ventilation.
One alternative is to pump from the doorway, but that's when the weight of hoses filled with concrete comes into play. “It isn't long before your crew's tongues are hanging out,” he says. Using old finishing pans as “saucers” helps the hose slide over rebar. But they often find using buggies is a better option to shuttle the concrete from the truck to the point of placement. This is particularly helpful in smaller retail buildings without large overhead doors.
The company owns three buggies and can haul as much as a cubic yard per trip. “In some cases, they're much more efficient than dragging around concrete hoses,” says Scott Swederski. “And they also help keep the injury rate down.”
Conveyors are another option. The Swederskis have found that using a truck-mounted conveyor can be the quickest way to move concrete. “It will move 300 cubic yards an hour, if you can keep the supply up,” says Scott Swederski. With a reach of up to 130 feet, provided by 3-, 4-, or 5-section telescoping booms, truck-mounted conveyors are well-suited to low clearance applications. They can handle a wide variety of materials, such as gravel and soil, as well as pervious concrete and other unpumpable mixes. At the other end of the scale, the Swederskis say they've also used conveyors successfully to move self-consolidating concrete, which is relatively fluid.
Even though pumps, buggies, buckets, and conveyors get the concrete close to its final destination, there usually remains some distribution and leveling to be done. One available laser-guided device mechanizes the final stages of concrete distribution before screeding and gets the concrete to within ¼ inch of grade. Requiring just one operator, it further speeds the pumping, or dumping, process because the concrete can be left higher than normal (see photo).
Another machine eliminates the back-breaking aspects of moving concrete hose. It straddles the concrete pump hose, lifting and moving it across the unpoured deck. The steering mechanism allows the wheels to turn almost perpendicular so it can move side to side as well as in line.
These are a few of the methods contractors can employ to move concrete more efficiently on the job. Knowing the site conditions ahead of time is the best way to make good plans and coordinate with your concrete supplier.
Working with your pumper
With so much of an emphasis on speed and flexibility, and the widespread preference to pump when possible, it's helpful to keep several things in mind.
- Communicate with your pumper days, not minutes, prior to the pour. That will help in identifying possible issues, such as site conditions, mix designs, and setup obstacles.
- Know what you need when you call. If you're going to use a system, know how much pipe you'll need. With equipment weight restrictions on highways, pumpers don't always carry extra pipe and may need to send a separate truck to deliver it to the site.
- Be aware of overhead obstacles and power lines. If only discovered when the pump operator arrives onsite, the whole delivery plan may have to be reworked.
- Allow enough time for the pump operator to set up properly. Half an hour before concrete is due should be ample time to work out setup issues.
- Eliminate the “rush” syndrome. Nearly every time there is an accident with a concrete pump on a jobsite it can be traced back to “hurry up.”
- Be aware of soil conditions that might not be able to support the pump's outriggers.
- Let the pump company know what type of mix they can expect.
- Be sure your crew knows how to work safely around concrete pumps. The American Concrete Pumping Association has a great co-worker safety manual. Also, request ACPA-certified pump operators. A properly trained operator can ensure a safe and efficient concrete placement.