On the typical concrete pour, your goal is to place the concrete as close as possible to its final destination—not only to save hauling time and boost productivity, but also to avoid overhandling the concrete. But on many concrete jobs, the ready-mix truck can’t gain access to the work site. When you’re placing a stamped concrete patio in a fenced backyard, a decorative floor inside in an enclosed building or working on a high-rise building, you must find another way to move the concrete from the truck to the point of placement.
Pumping is an efficient, reliable and economical means of placing concrete, and sometimes the only way of getting concrete into certain locations. Other times, simply the ease and speed of pumping concrete make it the most economical method of concrete placement. In the end, the convenience of easy access for truck mixers must be weighed against the desirability of locating the pump closer to the placement point.
HOW CONCRETE MOVES THROUGH THE PUMP LINE
When concrete is pumped, it is separated from the pump line walls by a lubricating layer of water, cement and sand.
Naturally, the concrete mix must be suitable for its particular application, but it must also contain enough water for the mix to move easily through the reducers, bends and hoses found in most basic pipeline setups. Pump primers can greatly reduce issues associated with pumping concrete and help pumping lines last longer. (Slick-Pak Pump Primer from Fritz-Pk)
It is important to have all concrete mixes specified as “pumpable” prior to any concrete pours. There are mixes that do not pump at all or cause the pump lines to clog. This can cause big problems if you have 8 trucks arriving on the job ready to discharge concrete. See more about removing blockages.
PROPER SIZING OF LINES AND EQUIPMENT
In order to optimize the concrete pumping operation, the most efficient configuration of the system must be determined. The correct line pressure must be determined to move concrete at a specified rate of flow through a pipeline of a particular length and diameter. The major factors affecting pipeline pressure are:
- Pumping rate
- Line diameter
- Line length
- Horizontal and vertical distances
- Configuration, including reducing sections
In addition, a number of other factors must be taken into account when determining line pressure, including:
- The vertical rise
- The number and severity of bends
- The amount of flexible hose used in the line
Larger-diameter pipelines require less pumping pressure than smaller-diameter pipes. However, there are disadvantages to using the larger conduits, such as increased blocking, bracing and labor needed. Regarding the concrete mix in relation to line diameter, the maximum size of aggregate should be no larger than one-third of the diameter of the line, according to ACI standards.
Concrete being pumped through a line experiences friction with the internal wall of the pipeline. The longer the line, the more friction encountered. For longer pumping distances, the use of smooth-walled steel pipe can lower the resistance. The length of hose used at the end of the pipeline adds to the overall line length as well.
Horizontal distance and vertical rise:
The farther or higher the concrete needs to go, the more pressure it will take to get it there. If there is a long horizontal distance to cover, one option is to use two lines and two pumps, with the first pump feeding into the hopper of the second pump. This method may be more efficient than a single, long-distance line.
Bends in the line:
Because of resistance encountered with changes in direction, the pipeline layout should be designed with the least number of bends possible.
Resistance will also increase if there is a reduction in pipe diameter along the path the concrete travels. Whenever possible, the same diameter line should be used. However, if reducers are needed, longer reducers will cause less resistance. Less force is needed to push concrete through an eight-foot reducer than through a four-foot reducer.
TYPES OF CONCRETE PUMPS
Boom trucks are self-contained units consisting of a truck and frame, and the pump itself. Boom trucks are used for concrete pours for everything from slabs and medium high-rise buildings, to large-volume commercial and industrial projects. There are single-axle, truck-mounted pumps used for their high maneuverability, suitability for confined areas, and cost/performance value, all the way up to huge, six-axle rigs used for their powerful pumps and long reach on high-rise and other large-scale projects.
Booms for these trucks can come in configurations of three and four sections, with a low unfolding height of about 16 feet that makes it ideal for placing concrete in confined areas. Longer, five-part booms can reach up or out more than 200 feet.
Because of their reach, boom trucks often remain in the same place for an entire pour. This allows ready-mix trucks to discharge their loads directly into the pump’s hopper at one central location, creating a more efficient jobsite traffic flow.
Most manufacturers offer a variety of options, on chassis and pump size, boom configurations, remote control, and outrigger options.
These versatile, portable units are typically used to pump not only structural concrete, but also grout, wet screeds, mortar, shotcrete, foamed concrete, and sludge.
Pump manufacturers offer a variety of different line pumps to meet a wide variety of needs. Line pumps typically employ ball-valve-type pumps. While the smaller models are often called grout pumps, many can be used for structural concrete and shotcreting where low-volume output is suitable. They’re also used for repairing underwater concrete, filling fabric forms, placing concrete in heavily reinforced sections, and building bond beams for masonry walls. Some hydraulically driven models have pumped structural concrete at outputs exceeding 150 cubic yards per hour.
Cost for ball-valve pumps is relatively low and there are few wear parts. Because of its simple design, the pump is easy to clean and maintain. The units are small and maneuverable, and the hoses easy to handle.
For more information on line pumps, see Concrete Pumps Buyer’s Guide.
Separate placing booms:
Separate concrete placing booms can be used when a boom truck is unavailable, or in situations where a boom truck may not be able to conveniently access the pour site. Combined with the right concrete pump, these placing booms provide a systematic method of concrete distribution.
For instance, contractors can use the truck-mounted pump with a placing boom in its conventional mode for part of a day on slab pours or other ground level placements, then quickly remove the boom (with the aid of a tower crane) for remote placements later in the day. Typically, the boom is remounted on a pedestal, which can be located hundreds of feet from the pump and connected with a pipeline.
Here are some mounting options for placing booms:
- Cross frame: Foundation mounting with bolted cross frame.
- Crane tower mount: Boom and mast mounted on crane tower.
- Side mount: Mast mounted to the side of a structure with brackets.
- Wedge mount: Boom and mast inserted in floor slab with wedges.
- Ballasted cross frame: Zero elevation ballasted cross frame. This method may also be used with the boom mounted on a freestanding mast.
- Anchored: Boom and mast are anchored to a supporting surface.
Click here to review diagrams of the above listed separate placing boom options. (Courtesy of Schwing)
Aside from normal jobsite precautions, there are a number of safety concerns specifically related to concrete pumping, such as keeping you machinery in good working order, truck positioning and stabilization and proper cleaning procedures. Learn more about concrete pumping safety.