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Ordering concrete in smaller quantities can be an expensive inconvenience. Large ready-mix fleets don’t like short loads, so you must pay for a minimum quantity regardless of your needs. With concrete in short supply in many parts of the country, ready-mix fleets can give priority to large pours.

But there are solutions tailored to small pours. Despite being a well-kept secret, volumetric mobile mixers have a well-proven history. “I saw these mobile mixers when I was over in South Korea in the early 1960s,” recalls Don Mullin, owner, Concrete Express of Salem, CT. These trucks produce concrete on site. “We used these trucks to build runways. When a truck was empty, we would simply go back and refill it with sand, stone, cement and water and return to the site.”

Mobile mixers are basically self-contained batch plants on wheels. “It is a mobile mixing unit which carries — in separate bins — sand, stone, cement and water,” says Mullin. These ingredients are precisely metered into the mixing auger to produce the appropriate mix design.

In the early 1970s, volumetric mixers were viewed as the future, but problems with metering systems created maintenance and quality issues that relegated this technology to niche markets. Since then, there have been many improvements and innovations that have resulted in a reliable and consistent product, according to Mullin.

Volumetric mixer fills niche

In 1991, Mullin decided to go into business and the volumetric mobile mixers offered a niche business opportunity. “The ready-mix trucks are not equipped for and do not want to deliver small yardage,” says Mullin. “They cannot send a mixer with an 11-yd. capacity to deliver 1/2 or 1 yd. of concrete. Financially, it just doesn’t work. You are restricted to the fact that you have to take 5 to 8 yds. from a ready-mix company in order for them to turn a profit.”

Mullin started the business with two Elkin trucks. He also helped six other individuals start up in the business, each with two trucks. “The advantage is there for a small truck to mix at your site in the amount that you require,” he explains.

Bob Maine, owner of Short Load of Fort Pierce in Florida, has been in business since 1987 to serve the needs of customers with smaller jobs. “The barrel trucks are looking for the big, quick yardage where the batch mixers cater to smaller contractors,” he says. The company currently runs a fleet of nine Cemen Tech trucks.

The smaller size of these batch trucks tends to be an advantage. A single-axle truck is able to get into many places that are virtually impossible for a full-size ready-mix truck.

An efficient solution

Efficiency is a key attribute of the volumetric mixer. “You don’t need a place for waste materials that are left over in a barrel truck because you don’t have waste with a volumetric truck,” says Maine. “You leave the materials in the truck and use them at another time.”

Maine reports that 10 yds. worth of materials fit in his Cemen Tech trucks and he claims it produces the same quality concrete as a ready-mix truck. “It is just that it doesn’t pour out as quick as a barrel truck. You can spit a barrel truck out in almost 10 minutes where these mix on site trucks usually take a half hour.”

Mullin reports his Elkin mixer is capable of producing 30 or 40 cu. yds. an hour. This production rate is more than typical customers seeking small pours can handle.

“Generally, on small yardage pours there is a little bit more detail work involved,” says Mullin. “It is generally finish work that has to be minded and then made presentable as opposed to just pouring it in a large form for a floor or a wall.”

Since the concrete is mixed at the site, there is a little more time to get everything set up properly without having to worry about concrete hardening in the mixer. “We do want to get in and manufacture what you need at the site and get out, although we don’t rush people,” says Mullin. “If they need the time, they will be afforded the time.”

Concrete quality

Since the concrete is manufactured on site, freshness is not a concern. “You have more curing and drying time,” says Mullin. “Water or additives don’t have to be constantly added to extend the drying time.” This helps ensure the quality.

Making the concrete on site also allows you to customize the mix to match the conditions. “If one particular area needs it a little wetter or a little drier, all we do is regulate the water as we are mixing,” says Mullin.

While the slump can be adjusted, you are limited by the aggregates on the truck. “You can customize the mix design, but you cannot adjust it from a pump mix to a 3/4 mix on the jobsite,” says Maine. “That would entail emptying the rock side of the truck and putting a different size rock on.”

Training required

Training has to be addressed with volumetric mixers. “It is absolutely essential that you gain the experience of learning how to operate one of these machines before you attempt to do it yourself and expect to get good results,” says Mullin. He recommends continuous training.

Maine agrees, noting, “It takes a minor training period to introduce somebody to this since they are not well known. Not a whole lot of people have seen these types of trucks before. It takes us maybe a week introduction to get a guy used to what I am looking for.”

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