Concrete Placement How-Tos: Economy & Efficiency

Concrete is one of our most common building materials. Its use in construction applications continues to expand as both the equipment and scientific sides of the business improve mix quality and placement technology.

Getting down to basics, there are two basic ways to put concrete where you want it. You can dump it or you can pump it. If you ever worked a job site that involved spreading dumped concrete you know it's hard labor-intensive work that kills your back and makes your muscles scream. If it's a hot summer day the material starts to harden before it's where you want it. By then, raking, screeding, pushing, or coaxing the material to move is next to impossible.

Concrete is a fantastic building material but it's not always the easiest to handle. Dumping the mix from a truck directly into a form using chutes, wheelbarrows, buckets, or other placing devices can be a long slow process that leaves you with a finished product that is less than acceptable.

For large flat areas like roads, sidewalks, paths, and parking areas, paving machines are the most economic and efficient way to do the job. Pumping concrete is probably the way to go for many other applications. It's a very efficient and reliable means of placing concrete and very economical as well.

In many of today's applications a pump is the only way of placing concrete where it's needed such as a high-rise building, or large slabs where the mixer truck chutes can't reach. Other times, the ease and speed of pumping concrete makes it the most economical and efficient way to put the material in place. There are concrete pumps capable of delivering more than 200 cubic yards of concrete per hour.

Other benefits associated with pumping include the fact that it keeps the concrete mix from segregating and the aggregate evenly distributed. Getting concrete where you want and need it is simplified with a pumping system. Simply put you can drag the hoses where you can't drive the truck or put chutes. You can put an elaborate patio or swimming pool in a landscaped backyard without destroying the landscaping by pumping the concrete to the site. You can pour floors or basements after a building has been erected.

The many cost-saving benefits have made concrete pumping a popular, economical and efficient was of handling and placing concrete.

When concrete is pumped through the pump line, it is separated from the pump line walls by a lubricating layer of water, cement and sand. 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 pipeline which consists of hoses, couplings, reducers, bends, and distance. It is important to have all concrete mixes specified as "pumpable" prior to any concrete pours. The pumpable mix must meet the design specifications of the job. There are mixes that can't be pumped and attempts to ignore this fact will result in clogged hoses and could ultimately result in damage to the pump itself.

There are a variety of concrete pumps from which to choose. You have several options. You can buy and own your own pumping equipment; you can rent or lease it; or you can subcontract with a professional pumper for a job. Pumps vary in size from small to self-contained boom trucks. Small line pumps can transport to the job site on a trailer or truck. Basic pumps cost around $20,000 and will go to about $60,000 for higher volume pumps with greater pressure. These are design for single operators and usually are remote-control operated.

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 are 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.

Selecting the proper pump depends on the type of work you are doing. To determine the right size pump you need to know the size of the aggregate used in the mixes, how many yards of concrete are placed per hour, and how far the concrete has to be moved from the pump both horizontally and vertically.

The smallest line pumps can deliver 5 yards of concrete per hour, with the largest pumps moving 60 yards per hour. You have a choice of power including gasoline, diesel or electricity. Most contractors use diesel-powered units. Electric driven pumps are a better choice for inside applications.

Smaller line pumps use mechanical ball valves to control the pumping action. Larger pumps are hydraulic, which allows them to deliver higher pressure.

In addition to stand-alone pumps there are a few that are available as attachments for some construction machines like the skid-steer loader. You would need to fit them to the job as you would with a stand-alone unit or a self-contained boom truck. Recently Blastcrete reintroduced a peristaltic pump as an attachment for skid steer loaders. Peristaltic describes the action that moves material through a tube or hose. It's similar to what happens when you squeeze a tube of toothpaste. Peristaltic pumps use rollers to squeeze the material toward and out the tube's open end. In this arrangement, the hose keeps the material confined and prevents the machinery from coming in contact with whatever it's moving.

The most common and practical way to pump concrete is with a boom truck. They 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. They range from single-axle truck-mounted pumps used for their high maneuverability, suitability for confined areas and cost/performance value, 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. This low unfolding height is 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 and helps to create a more efficient jobsite traffic flow.

Most manufacturers offer a variety of options, from chassis and pump size to boom configurations, remote control and outrigger options.

Separate concrete placing booms can be used when a boom truck is unavailable, or in situations where the 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 use the truck-mounted pump with placing boom in its conventional mode for part of a day on slab pours or other ground-level placements and 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.

Putting concrete where you want it can be accomplished in a wide variety of ways. The question is how much you want to spend getting the job done. Manual labor is expensive and not necessarily efficient. In so many applications concrete pumping accelerates the placement process to such a degree that it more than offsets the costs. It reduces time not only in the placement but also with finishing because the pour usually ends up with a much better finish.

Don't tackle a concrete pumping job without the advantages of experience, either your own or through a subcontractor. Concrete is a perishable product and certainly you don't want to waste any by learning how the hard way. Consult with a professional before making any pumping decision. The American Concrete Pumping Association (www.concretepumpers.com) can provide you with all the information you could want on the subject.

On a final note, remember, carelessness in the field can cause accidents, no matter how many safety measures are built in to the equipment and procedures. Keep these safety "don'ts" in mind:

DON'T

• Open a coupling that is under pressure.
• Face an open discharge end of the pipeline.
• Pick up a clogged hose that is under pressure.
• Climb on a hydraulic system to clean a clogged line.
• Operate a pumping system without being trained.