Making Concrete On-site

Tired of paying workers to stand around waiting for the ready-mix truck to bring your concrete? A volumetric mixer that lets you make concrete as needed on the jobsite might be the answer, particularly for contractors doing smaller jobs.

What is a volumetric mixer?

A volumetric mixer or mobile batch mixer is a machine that can be taken to jobsites and used to produce concrete or masonry grout. You might think of these mixers as mini-concrete plants. They are capable of making any type of concrete desired by adjusting the materials put in the mix. What is different in this approach compared to buying concrete from a ready mix plant is that the user buys the components needed to make concrete and mixes them himself on-site instead of buying premixed concrete.

There is almost no concrete waste with volumetric mixers because only the amount of concrete needed for the specific task is made. Dealing with leftover concrete has become an environmental issue because of the limited places for safe disposal, so there is value in avoiding excess concrete production.

Having a volumetric mixer eliminates concrete quality problems caused by traffic jams or ready-mix truck breakdowns.

"A drum truck has a limited amount of time for them to drop their load or it becomes what they call a hot load, and the only way they can make that usable is to add water and then your strength goes down," says Stan Horning, Global Mixers' sales director for the Midwest and West.

Using a volumetric mixer means the concrete is always fresh and the contractor pays only for what is produced. "It gives you the versatility to be able to create your own mix design and to mix on the jobsite as you need it," explains Dave Grant, vice president of sales for Elkin Manufacturing.

The voluminous materials move from the front to the rear of the truck and discharges into the mixer.

"Your material hopper has strike gates that control the volume of the sand and rock that enter the mix," says Horning. "Your cement has a constant flow and you change your mix design by the amount of sand, rock and water."

When the concrete comes out of the mixing auger it is ready to use. If different mix designs are required on the same job on the same day, they can be created easily by adjusting the gates. Depending on mixer capacity and mix design, these mixers can make up to 60 yds. of concrete per hour. Mixer sizes range from 2 to 10 cu. yds.

Elkin makes standard production machines or custom mobile mixers to specifications based on the needs of each customer. Patented special features include a cement metering wheel system which keeps close tolerances on cement delivery and an auger system where the auger boot and end bearings are adjustable to maintain concrete mix consistency as the auger wears.

Global uses a modular manufacturing process where all the major components are manufactured separately. "The steel is cut, fabricated, welded and painted before assembly," says Horning. "Ours is a bolt-on system. What that does not only aids in the anti-corrosive nature of the product, but everything is interchangeable." This feature makes repairs easy.

Silo mixers

Another type of jobsite mixer is the silo mixer. Silo mixers are portable but not mobile because they have no wheels. They are sold separately from the silos that contain the concrete ingredients and are compatible with any brand of silo.

Silo mixers are transported to jobsites on pickup or flatbed trucks. Once at the jobsite, the silo mixer is placed beneath the silo by a rough terrain truck, which is a large forklift. The mixer is raised by the fork truck until it reaches the proper height under the silo.

"Our silo mixers have an A-frame and as you raise the mixer, the platform gets wider and is more stable as it gets higher," notes Ed Varel, engineering project manager for Stone Construction Equipment, Inc. The platform has fork pockets under it so it can be picked up from any side. The mixer's legs slide inside each other telescopically. Once the mixer is properly positioned, the operator removes the pins to drop the legs, which lock in place, and the fork truck is removed. The concrete mix will go directly from the silo into the mixer.