Determining how best to set up a pumpline system for concrete isn’t usually the concrete contractor’s responsibility; you leave it to the experts. It’s one of those details the concrete pumping contractors usually cover as part of their scope of work. But like everything in concrete construction, contractors should know the basics for all aspects of the work.
Setting up a pumpline can be as simple as rolling out a small diameter hose on a jobsite and connecting it to a concrete pump. But it can also be as complicated as placing concrete 1000 feet above ground, running it through bends cast into thrust-blocks, and stand pipes expanding and contracting several inches per day while being secured to the structure. The latter requires careful planning.
Closely related to the success of a pumping system is the concrete mix. The mix and the line must be compatible so placement can proceed in a straightforward manner. Pumping companies and those who design pumpline systems often have little voice in the design of mixes; the project requirements for concrete govern that. But communication is necessary to achieve a good delivery system. Steel pipes, or slicklines, must be the proper size and the proper type of pipe with the right wear properties in relation to the concrete mixes to achieve good productivity at the right price.
Safety is always a consideration, too. A plugged line can result in high line pressures, putting everyone nearby at risk. Safe pumplines involve both the proper design and safe work practices.
Designing the mix
Gary Brown, operations manager for R.L. McCoy, Indianapolis, says the best concrete for a job and the best concrete for a pumping operation are sometimes diametrically opposed. “The easiest concrete mix to pump has a high water-cement ratio with as much portland cement as possible. Water-cement ratios of 0.45 or more are the easiest to pump and using a superplasticizer to achieve higher placing slump doesn’t help much. Pozzolans, however, can be helpful as a portland cement replacement.” But the best concrete for a project may require a low water-cement ratio and cementitious amounts calculated to increase compressive strength and reduce shrinkage.
Aggregate is an important consideration in the design of a pumpline. The pipe or hose diameter for a project should be at least three times larger than the diameter of the largest aggregate. So for instance, if the largest aggregate in a mix is 1 inch, the minimum diameter for the line is 3 inches.
Brown says the aggregate gradation of a concrete mix is also a concern. Gap-graded mixes are more difficult to pump and wear out pumplines (and pumps) faster than well-graded mixes.
The amount of aggregate in a mix also affects pumpability. According to Brown, a pea gravel mix consisting of 1100 pounds of coarse aggregate is about all that a pump with a 2-inch line can handle. If a 1-inch top size aggregate mix is used the approximate total weight of aggregate shouldn’t exceed 1800 pounds/cubic yard—aggregate source is an important factor here.
Designing the system
From their extensive field experience with pumping concrete, most pumping contractors and concrete contractors are competent to lay out pumplines for typical applications. But there are many situations requiring expert help.
Residential footing and foundation placements are among the most straightforward. Most foundations can be pumped directly from a boom truck, making set-up and clean-up simple. It’s important, however, that pump trucks be set up on stable ground, not on uncompacted fill—what’s safe enough to support a truck is not always clear. When pump trucks can’t get close enough, or find stable ground close enough, to place concrete with their booms, lines must be set up. Foundation contractors often prefer flexible hose instead of slickline for this. Kyle Rask, director of safety and risk management for Brundage Bone, Kent, Wash., says 400 to 500 feet is about as far as you can reach with a flexible line.
Commercial applications can be more complex. Depending on the experience of the contractor or pumping company, a pumping consultant is sometimes involved when specifications are being developed, when contractors are bidding the job, or when it’s close to the start of construction. High-rise buildings require the most expertise. John Schantz, chief engineer for ConForms, Port Washington, Wisc., a supplier of abrasion-resistant piping systems, says it’s because on commercial projects, concrete is typically pumped longer distances and at higher pump pressures.
Projects placing higher concrete volumes require additional planning for pumplines. Schantz says his company provides pumpline design as part of what they offer a client, with high-rise projects being a large percentage of this work. One of the first considerations is how long the pipe needs to last. Lines on big projects can be in place for a long time and contractors don’t want to replace them while a job is in progress. Selecting the type of pipe to use depends primarily on the amount of concrete yardage involved and the type of aggregate being used—wear is considerably higher in some parts of the country due to local aggregates. “Pipe wear can be up to five times more depending on a project’s location,” Schantz adds. The pressure required to move concrete to the point of placement is also a factor. In a typical 5-inch standpipe, moving concrete 1 vertical foot requires approximately 1.1 pounds of pressure. Pumping concrete 1000 vertical feet therefore requires a minimum pressure of 1100 psi.
Once wear and pressure factors are calculated, a decision can be made on the type of pipe. Brown says pipe is often selected based on its expected life, the goal being to choose pipe that will last through the project but wear out by the end. The highest wear, highest pressure pipe is “induction heated, single wall” pipe and couplings, used for high-rise construction projects. It can handle pressure up to 5000 psi and beyond.
Twin-wall pipe is the most wear-resistant and is commonly used on boom trucks and placing booms. But it’s rated as low-pressure pipe, typically operating at pressures below 1250 psi on booms. The inner layer of this pipe is harder, more brittle steel and therefore more wear-resistant, while the outer layer is softer and more ductile.
Projects such as high-rise buildings require riser pipelines to be permanently anchored to the structure for the duration of a project. Pipe bends or sweeps are secured by casting them through concrete “thrust blocks,” preventing the pipe from moving due to the forces of the concrete moving in the line.
It’s also common for high-rise projects to include placing booms, often mounted on top of self-rising core-forming systems. Buildings with larger deck structures may have two or more placing booms, so included in the installation might be diversion valve systems at ground level, directing concrete from one standpipe to another, adding to the complexity of a system.
Designs for pumplines intended to remain in place for the life of a project, such as high-rise construction, must also include ways to clean the line and dispose of the concrete. A 100-foot long section of 5-inch line holds about 1/2 cubic yard of concrete. By the time the One World Trade Center project in New York City tops out, filling the slickline to deliver concrete will require about 10 cubic yards of concrete. The usual way to empty the line after a placement is to include a diversion valve to empty the line back into a ready-mix truck. Cleaning uses compressed air, blowing out the standpipe from above.
Monitoring line wear
Brown says it’s difficult to judge wear in flexible line because abrasion to inside surfaces isn’t easily detected. Wear can lead to a rupture, especially if workers inadvertently cause hose lines to kink, causing pressure spikes.
Monitoring pipe wear is important, so concrete pumping companies like Brundage Bone and R.L. McCoy have testing programs to monitor wear. Brown says twin-wall pipe wear is more difficult to judge than single wall pipe. “The usual testing devices don’t work so visual inspection and using calipers to measure pipe thickness at its ends is all companies can do.” Most pumping contractors keep yardage records for all their equipment and use the information to help them decide when maintenance or replacement is necessary.
Safety first or safety second
When placing concrete with a concrete pump and the line plugs up somewhere, the response is often a frantic one. Everyone scrambles to find where the line is plugged; breaking sections of hose or slickline apart in the search for the problem location. The problem needs to get fixed and concrete moving as fast as possible before a plug develops somewhere else. With flexible hose, workers often jump on the line feeling for hard spots. They might use sledge hammers to pound on the hose to break up clumps and get the concrete moving. It’s an exhausting, back-breaking effort, working against the clock.
During all this activity there sometimes isn’t much thought given to safety. The objective is more one of “fix the problem now,” and think about safety later. The better approach is to conduct safety training sessions, carefully plan for pumpable concrete mixes, make knowledgable decisions on line design, and have experienced pump operators. All of this taken together is the proactive way to the best outcome.
When thinking about pump safety, consider the following:
- Pumps are built to deliver constant volume. When a line plugs, pump pressure instantly spikes to the pump’s maximum capacity in order to keep output volume constant.
- Pump operators must constantly monitor line pressure. When problems arise, line pressure should be relieved before workers start troubleshooting.
- Pipe bends are a point of high wear so frequent inspection is important.
- Workers should work with their back to the pumpline whenever possible.
- Workers should remain a reasonable and prudent distance away when air is introduced into a pumpline for any reason. Wait until a steady flow of concrete resumes.
- Position a laborer at the hopper when the pump operator is at the point of placement to be sure lumps, foreign material, and air doesn’t get into the hopper due to low concrete levels.
- A small number of project owners still specify unsafe practices, especially regarding boom pumps. Address any issues before a job starts.
- Never attach any metal device to the end of a hose.
- Horizontal lines wear much more quickly than vertical lines.
- Pumps, especially boom pumps, should be set up on ground as level as possible and must rest on stable subgrade to avoid the risk of tip-overs.
- Pump outriggers should always be fully extended.
- Pumps near excavations should be located at least 1 foot away for every vertical foot of drop.
- Workers must have stable footing near hose ends when placing concrete.
The American Concrete Pumping Association (ACPA) suggests that the operator on your job be ACPA certified. Certified operators must complete an intense ACPA safety training program that includes special emphasis on the hazards of air getting into the delivery system (see A Word About Hose Whipping). ACPA’s website, has a special Contractor tab with free downloadable safety information.
Be kind to the line
When we think about concrete pumping we automatically focus on the concrete pump. There isn’t anything romantic about pumplines; they are just a collection of tubes. But pumplines are the delivery mechanism contractors works with. They are carefully designed to provide good, safe service with few problems. When all goes well, it’s natural not to think about them—that’s the way it should be.