Although batch plant concrete has been the industry standard and the most familiar method of mixing, distributing, and pouring concrete for many years, continuously mixed concrete devices have been around for more than a century.

As reported by Jane Morley in Concrete International, Frank Gilbreth patented a gravity-fed mixing device in 1899. Simple, inexpensive, and easy to quickly set up, it featured non-moving interchangeable parts and a slightly angled slope that allowed materials to flow slowly so the operator could evaluate the consistency and produce a uniform mixture of cement, water, and aggregate. To demonstrate the device’s value, Gilbreth produced samples indicating a compressive strength of 4,300 psi, as compared with 3,500 psi for the same ingredients mixed by hand. Gilbreth faced a handful of competitors until 1909, when a horse-drawn concrete mixer challenged his invention. By 1920 contractors were mixing concrete on trucks in transit, but it was another 40 years before the next major innovation revolutionized the industry.

Harold Zimmerman patented his first mobile concrete mixer in 1964, and, as current Zimmerman Industries Inc. President Jerry Stoner puts it, all competitors’ models derived from Zimmerman’s initial design. “It changed the industry,” he says of the mobile volumetric mixer. However, the industry hid in the shadows of the niche market for much of the subsequent 40 years.

“Mini-Mobile Batch Plants” for Cost-Effective Onsite Concrete Production
The mobile mix concrete technique stores dry ingredients necessary for the production of concrete—aggregate, sand, cement—as well as pigment and admixtures in separate compartments in the machine, typically mounted on a truck or trailer. Driven to the job site, adjustable controls meter the quantity of materials for specific mixtures before materials are conveyed to the mixing auger, where water is added. Thoroughly blended, the ingredients are volumetrically proportioned to deliver a specific, controllable amount of material at a constant rate.

Historically, according to the Volumetric Mixer Manufacturers Bureau, or VMMB (est. 1999), these machines have been used predominantly for production and delivery of small amounts of concrete: short loads as small as half a cubic yard. But as contractors recognized its benefits, use and acceptance of—and demand for—volumetric mixing increased dramatically. Initially a consumer-oriented retail trade for homeowners and small contractors, the volumetric mixing industry has expanded beyond niche markets.

Benefits of the versatile system are manifold: reduction of waste, downtime, and costs; accuracy; and higher-quality concrete. Because the materials are mixed when and where needed, the concrete is always fresh and there’s no waste. Nor is there any waste of manpower. “It’s a one-man operation. It’s a very cost-effective way of pouring concrete.” Fillmore calls it a “batch plant on wheels.”

Dave Grant, vice president of sales for Elkin Manufacturing Inc., believes the main advantage is the ability to pour any strength or any mix design and to immediately change the mix. “Contractors can even pour different mix designs in the same load,” Steve Fillmore, who is in sales and marketing for Reimer International Inc. in Alberta, Canada, elaborates. That and the ease of cleaning make it particularly suited for color.

Photo: Cemen Tech

A "batch plant" on wheels.

Grant also notes that operators have better control over the product, an important asset to the time- and labor-saving aspects of business. “More and more, that’s the reason contractors are doing it. You have to schedule so far ahead for delivery of ready-mix. If you have to cancel due to weather or some other reason, you have to wait to reschedule. These guys are busy; they can’t wait."

Mixers Spawn New Business Opportunities
Tom Roman, owner of Quality Concrete in New Jersey, is one of those busy guys who can’t afford to wait for delivery of ready-mix. With several crews working in new residential subdivisions on the “back end,” doing post-construction fixes and repairs, the contractor has a tight schedule to maintain. But he was “constantly waiting on concrete.” Conceding that the New York area is a busy one, he nevertheless contends that he’s a good customer, spending an average of $500,000 a year on ready-mix. But the plain-speaking business owner complains, “I got crappy service. They make money with a full truck, but I’m only doing 2-, 3-, or 4-yard pours for driveways and curbs.

”Elaborating on Roman’s observation that batch plants make money on full-load deliveries, Jay Esterly of Esterly Concrete in West Reading, PA, explains that “the big guys don’t do small jobs until the end of the day, when they’re done with the big jobs.” Watching people with small jobs become exasperated by the delay, he saw an opportunity. As Fillmore pointed out, contractors cannot afford to pay crews to wait for concrete. To solve their common problem, both Roman and Esterly bought Zimmerman mixers. For both men, the addition of the concrete equipment unexpectedly led to new business opportunities.

Photo: Cemen Tech

One advantage of volumetrically mixed concrete is unlimited transport time.

For 30 years Esterly relied on pre-cast concrete for the manufacture of burial vaults. Skid-mounted volumetric mixers have benefited the pre-cast industry by producing a consistent mix in specific quantities and colors, enabling companies to control costs and reduce waste. After Esterly purchased a mixer for company use, a side business spun off and soon became the heart of Esterly Concrete. Now with three brand-new trucks on the road delivering concrete to homeowners and small contractors, the company is busier than ever.

He’s convinced the key to his success lies in his ability to get to the small jobs early. “Reading is a huge city, but I can take a 9-yard truck and do three jobs quickly” because the trucks can make multiple stops without reloading, even if those stops require different mix designs. Esterly, who pours a lot of sidewalks, patios, curbs, and garages, says he can pour 2,500 psi for a footer and 4,000 psi for a garage out of the same truck on a single run.

Similarly, owning a mixer has changed the way Quality Concrete does business, Roman claims. “Any contractor that does sidewalks or other flat work has to have one. Any medium-size guys need one. They’re magic ATM machines: You put sand and stone in the front and cash flows out the back. We’re talking 120% mark-up on retail.”

Tired of waiting for concrete delivery from the ready-mix plants, four years ago Roman bought a small used unit with a silo for storing powder. However, he says, “We know what good concrete looks like, but we didn’t know much about the machine.” In desperation, he called the phone number on the side of the truck and Zimmerman sent someone out to train them.

The mixers do require a higher degree of training to properly operate. Because each truck is, in essence, a mobile batch plant, every driver is, therefore, a plant operator. Stoner believes training is an industry weakness, so in an effort to help the industry and raise the bar, Zimmerman conducts annual training classes open to everyone with any brand volumetric mixer. “We spend considerable time training every new customer. We go over everything, we calibrate the machine, and we watch them make concrete before we leave. We’ll even help them with a business plan if they want.”

Training made all the difference for Quality Concrete. “They taught us the concrete business. It was unbelievable,” Roman marvels. “Production went up. Profits went through the roof. People started calling us for concrete. We didn’t even know what to charge!” Within three months, Roman purchased a second unit from Zimmerman so he could service his own company’s needs and those of his new retail business. “I didn’t want to be in this business, but it’s lucrative. It’s a nice little $50,000-a-month add-on business.”

That’s typical, Stoner avers. “The cement shortage three years ago changed the industry dramatically. Batch plants started running allocations, and small contractors couldn’t get concrete. A lot of contractors bought machines to do small pours on their own jobs because they couldn’t wait on delivery. It saves time; it saves money. But what we’ve found is that contractors start selling concrete retail, first to urban residential customers, doing 5-yard pours or less. Pretty soon it grows. They’re doing 10- and 15-yard pours. They add a truck. So many of them buy a small machine for small customers and then turn around and come back for a bigger machine or more machines. We advise them to do market research before they buy, so they know what they’ll need.

“[Volumetric mixers] created jobs,” Stoner reiterates. “People bought the machines, created a livelihood, and started a new industry.” The rise of new entrepreneurs who might take business away from batch plants led to criticism within the industry and counterclaims that fear of competition has suppressed acceptance of the volumetric mixers. However, Tom Palme, president of Cemen Tech, insists they “complement ready-mix companies. It’s not either/or.” Others agree, identifying their biggest competitor as the hardware store. DIYers with small residential jobs are more likely to pour their own concrete because they can’t get small loads from a batch plant, and volumetric mix contractors are often too expensive.

Roman readily admits his product costs more than ready-mix, but his on-time scheduled delivery attracts a lot of residential customers who are unable or unwilling to pour their own concrete. In fact, retail business increased so much, Roman found himself back where he started: His crews couldn’t get concrete—this time even from his own company!In rapid succession, he purchased a third and fourth truck, again from Zimmerman. He started doing road repair—a popular implementation of volumetric mixers since the introduction of rapid-hardening concretes in the late 1990s. State departments of transportation (DOTs) like the new material because it’s strong enough to drive on within four hours, so lanes can be closed after the evening rush hour, resurfaced, and opened before the morning commute. However, because the mixture reaches initial set within 20 minutes, producing it onsite is imperative and thus lends itself to the volumetric mixer industry. “The laws changed and roadwork is all at night,” Roman adds. “It means more business for us, because ready-mix is tougher to get at night, and a lot more expensive if you can get it at all. Everyone started calling us because they couldn’t get ready-mix. We had to get a fifth truck.”

From Here to Eternity
Meeting the overnight demands of roadwork with quick-setting concrete is only one application well suited to the mobile mixer. Larry Hooper, owner of LPR Concrete in Three Hills and Drumheller, Alberta, Canada, uses the mixers when pouring pilings. The procedure requires that pilings be filled as the holes are drilled—often an all-day affair. But because ready-mix typically has a two-hour limit from batch to application, Hooper says most engineers reject loads more than two hours old. Unlike ready-mix, volumetrically mixed concrete has unlimited transport time, but for jobs like that, Hooper says the machine remains onsite all day, set up like a temporary batch plant mixing fresh concrete as needed.

Although best known in the small-pour milieu, mixers can also be practical in large-pour situations—particularly at remote locations. Hooper, who operates six 10-yard units and two specially made trailer-mounted units, can do onsite large pours more economically than ready-mix delivery. “We did a 230-yard pour at one location. We set up on the site and did the pour in six hours with three trucks. To haul from the closest plant, which was 20 miles away, would have required 29 loads of concrete and taken a total of 44 equipment hours. It would have required a one-hour cycle time at 8 yards because you can’t do 10 with the DOT laws, so to do it in six hours would have taken eight trucks. Instead, we supplied a large amount of concrete with minimal equipment and manpower.” In addition to saving fuel, time, and manpower, he points out the environmental issue of emissions, as well as concerns about road damage. Sometimes it’s a matter of heavy traffic slowing down delivery as much as distance. “The world is more competitive today,” Palme observes. “People can’t afford to wait on trucks. Rural job sites cause slow delivery times, but we have a bigger issue with urban traffic.”

Hooper says the mobile mixer “really shines” in large geographic areas with low population density. In fact, he’s now bidding on projects even farther away—projects more diverse than “just” pouring concrete. “Because of the nature of the machine, we can pursue other work,” he says.

Round Guys Versus Square Guys
“Ready-mix is a commodity-driven business,” states Don Mullin, owner of Concrete Express in Salem, CT. “Everybody recognizes them; they’re the guys with the big, round barrel trucks. We sell service, not a commodity. We’re the guys with the kind of ugly square trucks.”

He chuckles about his round guy/square guy theory but uses the imagery to illustrate his point. “It’s a different kind of business, and it’s not for everybody. We serve different markets. Ours is a specific market: small jobs. [The volumetric mixer industry] has been identified as a better alternative for small jobs because we do things they can’t do cost-effectively—like quarter-yard, yard, and yard-and-a-half pours.”

Another thing Mullin says the “round guys” can’t do is make adjustments in their mix “because the round guys dump it all into a barrel, either at the central mix batch plant or it’s a transit mix where they dump all the dry ingredients in and then turn the barrel counterclockwise en route. They can’t adjust to make it tighter. But once you’re a pickle, you can’t be a cucumber again. The round guys are always too wet or too dry; it’s the nature of the business. We square guys have more diversity because we manufacture concrete onsite. We can change the ratio as we go, and we can tailor the mix to any specs right in front of the customer.”

The ability of the mixers to produce fresh concrete at any slump, or even multiple slumps on the same delivery, gives it an advantage over ready-mix. Changing the ratio, or slump, is an important asset, particularly for small contractors in the residential arena. Steep spots like driveway entrances require a higher slump. A curb demands an even stiffer mix. The operator merely adjusts the volume of water added to produce a higher or lower slump, as necessary. Roman appreciates the control and versatility the mobile mixer affords. “Every stop we make is different. We may need 3,000 psi for a footing, 4,500 for a sidewalk, and rapid-set for highway work. We just set the gate and pour.”

Not only can the mobile machinery change mixtures at different stops, but it can also alter the mix during a pour. “On a long pour like a 150-foot sidewalk, we start really wet,” Roman explains, “but we’ll pour the last 10 to 20 feet dry so it all dries at the same time. There are a lot of tricks we can do with it.”

The Bottom Line Is the Bottom Dollar
Volumetric mixers are economical for contractor and customer. “It’s cost-effective because there’s no required minimum like there is from ready-mix companies,” says Grant. Many ready-mix consumers must pay for all the concrete ordered, not necessarily all the concrete used. Not only do you pay for only what you use with the mixers, you use only what you need—making them environmentally friendly as well as economical.

The consumer isn’t the only one avoiding waste. “If we send out a full truck but we use only half the load, it doesn’t matter. There’s no loss,” Tom Roman relates, because the ingredients can be stored in the truck until needed. Time as well as material can be saved. By loading the truck the night before, Roman says his crews can save time on the day’s first load—something that’s not possible when using ready-mix.

Nor can the “round guys” always squeeze into tight job sites. Volumetric mixers take up less space on the site, and travel better on driveways and in backyards. The space they consume at headquarters is also minimal: According to Mullin, all you need is a cement silo, a front-end loader, and an area to store materials.

The mixer’s versatility and efficiency have not only saved money; they’ve increased business for some. Hooper’s business has picked up since he got a mixer, due in part to his ability to submit lower bids because he’s not using batch plant concrete. He doesn’t worry about delivery time, setup time, freshness, or waste. In addition, he considers the product to be “the same quality as ready-mix” and perhaps better because “you can do specialty mixes.”

Beyond concrete pours, the “great flexibility” of the machines provides more work for LPR Concrete and its employees. “We got a trailer unit to free up a truck for oil-fuel hauling. We run the mixer truck in the summer and are able to use it in a different way in the winter. It gives my drivers employment and keeps the trucks on the road.”

Photo: Cemen Tech

Ready-mix—traditional, but not always the best

Competitors in Concrete
Within the volumetric mixer industry, close competition reigns. “The overall design of all units is the same,” claims Fillmore. But some companies have incorporated developments that give their equipment an edge. Stoner encourages customers to look at other brands. “We built the original and we’ve improved it since then. We’re innovators in the industry. I know what that first machine can do, and what the new machine can do.” Zimmerman machines offer more options than the competitors, he claims, like six chute options for different applications. A power telescopic chute can be raised and lowered or telescoped hydraulically. “You don’t have to move the truck or lift heavy chutes.”

Zimmerman is the only company offering a hot-water option, Stoner claims. “It’s ideal for cold weather. Concrete set time is proportional to the heat it’s poured at: The higher the temperature, the faster the set time.” The feature he’s particularly proud of is the patented positive-feed twin-chain drive system. “It’s totally sealed, can separate materials, can run independently, and requires one-fourth the maintenance of a conveyer belt feed system. It lasts longer too, which translates into more cost savings.” Realizing that Zimmerman isn’t the cheapest on the market, Stoner still believes Zimmerman offers the “best bang for the buck. One customer in Washington, DC, had our competitor’s machines, but shortly after they bought one of ours, they bought three more. Why? They’ve never been in the shop; they just keep running.”

Roman knows his Zimmerman machines are chain-driven, but he doesn’t know if that’s better or not. However, he remains “brand loyal forever” because of Zimmerman’s service. “Their service is great! If I pick up the phone at 4:00 on Friday, they’ll have a part here Saturday at 10.”

Service was only one of the incentives that enticed Esterly to purchase three Zimmerman mixers. “I looked at a lot of other mixers before I bought any. The others weren’t easy to maintain. I can calibrate my trucks in less than an hour.”

Different features attract other contractors. Mullin started his business with two Elkin trucks. Since then, he has helped start 10 other mixing companies and worked as a consultant. “I have choices every day on who I buy equipment from. Elkin has the only monitoring wheel in the industry. That’s a big difference that attracts me. Cement is expensive; it should be accurately dispensed. That’s critical.”

Grant describes Elkin’s patented metering wheel system. “It’s a precise design to meter cement—the most costly ingredient—to improve the consistency of the mix and the delivery. It meets VMMB standards.” Other features that set Elkin apart include a patented mixing auger system with an adjustable boot and end bearings that allow operators to maintain the same tolerances for mixes. “It’s a wear issue,” Grant explains.

Ch-ch-ch-changes
“Technology is making its way into the machines,” Stoner believes. “More people are getting into the business, and they want the machines to last longer and be simpler to operate.” Fillmore agrees, noting that although the basic premise hasn’t changed, engineering has led to more precision through features like hydraulics, allowing operators to produce a more consistent quality product. “That’s definitely more attractive to our customers.”

As the machinery changes, so does the industry. “The industry is changing as it grows,” Palme postulates. “The mixer is more popular and more widely accepted.” He credits that, in part, to the VMMB standards, first published in 2001. “This method was once looked upon as a special project. Now, it’s widely used. We’re breaking down the paradigm that cement has to be mixed in a drum.”

Hooper sees a shift in the industry. “Ten or 20 years ago, it was a niche market. But contractors have built on the small residential delivery market, and now it’s moving to the mainstream.” However, to continue on that path, he insists that pours must be verifiable. “To legitimize itself, the volumetric industry needs control devices that generate batch delivery tickets, using a digital connection that cannot be altered by the operator.” The devices keep drivers accountable for quality control and ensure that the machine is properly configured to produce and dispense the correct mix.

Devices like Reimer’s Hawk 6 processor track information about each pour: the number of yards, the mix recipe, including additives. “The addition of on-board micro-processing technology allows us to track output,” adds Fillmore. “It provides meaningful information on the product and provides data logging for inventory control. With this wireless electronic control, it’s just roll and pour.”

What was once considered only for niche markets has now gone mainstream. As Stoner says, although many contractors get into volumetric mixing in an attempt to capture niche markets, “This goes way beyond the batch plant!

Anything is possible.” Imagine what developments the next 100 years could bring.

Residing in Indianapolis, IN, Lori Lovely writes authoritatively on transportation and technical subjects.

GEC - January/February 2007

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