Making Concrete Panels the Modern Way

Panel dimensions and embed locations are downloaded from a CAD file to the automated plotter and transferred directly on to a clean pallet. Here, workers place rebar inside the shuttering molds.

A longtime maker of precast concrete products goes high tech in its new, automated panel-making facility.

Use of prestressed/precast concrete panels in the construction sectors has grown steadily since the 1950s. Today, these handy building blocks are used in all types of commercial buildings, in addition to parking garages, retaining walls, underground utility vaults, paving, and highway sound barriers. Chief among the panels’ many benefits is that they are made offsite and trucked to jobs, eliminating the need to build forms and pour concrete onsite. Furthermore, precast-panel manufacturing typically occurs in certified facilities that promise consistent quality, something that can be difficult to achieve with on-site pours.

The manufacture of precast concrete panels, however, has traditionally been a largely old-fashioned, manual process—conducted in a controlled environment, but still based on the same labor-intensive techniques that would be used anywhere else. With the help of advanced manufacturing technology, that is changing. The new, 33,000-sq.-ft. Molin Concrete Products plant in Ramsey, MN, just outside Minneapolis, is one example of how automation has redefined this manufacturing process and, in doing so, improved all aspects of concrete-panel production.

Molin, which began in 1897 as a masonry construction firm, evaluated several manufacturing techniques before choosing a design that was entirely new for the industry, said Matt Westgaard, chief operating officer for the firm, based in Lino Lakes, MN, also near Minneapolis. “We could have taken the conventional approach, but decided to go with a more automated, technical way of manufacturing that involves more equipment, computers, and machinery.”

This approach, though highly capital-intensive, removes virtually all of the hands-on procedures that have long been used to make precast concrete panels. These traditional methods include the use of stationary, flat table forms, into which concrete is poured by bucket or truck, and finished by hand. Panels are then “covered with tarps and allowed to cure out on the manufacturing floor,” according to Westgaard, who has 26 years of concrete-product experience, the last four with Molin (pronounced “mo-lean”). Under the new method, he said, “The form is brought to the concreting area where a concreting machine finishes the concrete. Then the mold is moved into a curing chamber where it is controlled in an optimum environment for a set period of time.”

A press release about Molin’s new facility—scheduled for a Sept. 2015 grand opening—describes it as resembling an “ultra-automated Mercedes Benz plant,” which may not be far off. Its German-made carousel system for moving the concrete panels, for example, is more typical of European plant design, and a rarity in the U.S., said Westgaard.

Conveyors automatically move panels from one production station to another, with each station performing a specific process. Other materials, such as steel reinforcement, are supplied directly to appropriate stations, and a central master-control system guides the operation, feeding production data directly to the automated machines. Computerized quality control is available at each station.

The new system is faster, safer, and more productive than traditional methods, and requires less floor space and labor. An older precast production plant, for example, would require about 48 workers to do the job. Only 18 will be needed in the new plant. The new plant’s output is expected to be 8,000 sq. ft. of precast panels a day, or three panels an hour, an improvement of approximately 40% over traditional output. The panels, all of which are custom-made to specification, typically range in size from 2-ft. square (though can be made smaller) to much larger. “The largest single piece we can manufacture is 12 feet wide by 38 feet long, up to 12 inches thick,” said Westgaard.

A single employee controls the concrete pouring bucket using an automated belt pack. In a traditional plant, this is a highly labor-intensive process requiring an entire crew to complete.

Meeting the need to advance

Molin Concrete Products today operates one other concrete-products facility, also in the Minneapolis area. According to Westgaard, company management based its latest decision to invest in a new facility less on cutting costs than “how we could eliminate the variables among our products and businesses, and drive some efficiency into the operation.”

Specifically, Molin personnel hoped to eliminate human-error mistakes, said Westgaard, and “really dial in the consistency of our concrete. With that, he added, “we really looked at equipment and automation in terms of how to get that consistency and repetition.”

A particular challenge in that regard is color consistency, which is “a big consideration on the curing and finishing side,” said Westgaard. Color is affected by many factors, including the concrete’s water-to-cement ratio, how it is cured, the rate at which it is cured, and the heat of hydration. The new plant simplifies all of these procedures and relies on modern equipment to maintain consistency throughout. Hydration probes and computer-controlled mixers that mix concrete and monitor viscosity, for example, remove the need for human intervention. All products are then “cured in a single chamber where both heat and humidity are controlled for consistency,” said Westgaard.

Once a pallet has reached initial set in the curing chamber, it is raised to a mezzanine. Using a belt pack, one employee is then able to control the automated helicopter trowel that replaces several finishers needed in a traditional facility.

Hiring and training

Molin began operations at Ramsey on a reduced scale in late spring 2015, three months prior to its scheduled grand opening. This was necessary to “get all of the equipment and new employees trained and familiar with how everything runs,” said Westgaard. The hiring and training process was deemed especially critical due to the new plant’s high-tech design. New hires were joined by experienced employees, including several maintenance technicians who transferred from other company facilities.

“Some of our new employees came with concrete experience,” said Westgaard, “but a challenge for both the maintenance and production folks was to not handle the process or concrete production in the traditional way. The thought process from manual production to a carousel system is quite different,” he added, “and the new team had to let the equipment do the work. Their instinct was to lean on past experience instead of allowing the new equipment to provide efficiency in the system, so there has been a little bit of a learning curve there.”

But the biggest adjustment for Westgaard and his team involved programming. “Our maintenance staff was highly trained and technical in terms of hydraulics, compressed air and motors, and conventional maintenance issues,” he said, “but [setting up here] really came down to circuit boards, circuitry, and computer programming.” Programmers from Weckenmann Anlagentechnik GmbH & Co., Dormettingen, Germany, the carousel manufacturer, spent several months on site with the Molin crew to assist with assembly, commissioning, and training. 

Westgaard also noted that, while finding qualified workers for the new plant did prove as difficult as he had anticipated, the process came with a silver lining. “We had an opportunity to bring in a large percentage of new employees early on,” he said. “This way, they could learn from the ground up as the plant was being assembled and commissioned. That’s not typical. Most precasters have an existing facility, and when they bring new employees into their operational setting, they have to get them up to speed. Because we brought in our workforce while the plant was still under construction, they could work with the equipment suppliers and learn about everything from the ground up. This proved to be quite efficient.”

After concrete is cast, an oscillating shake station consolidates the mix, and pallets are screeded off before being sent into the curing chamber.

Fine tuning for the future

As with any endeavor of this scale, new challenges were part of the daily routine. The Ramsey facility, for example, was not ground-up construction but a rehab of an existing building that had been vacated by another concrete company several years earlier. “Some of our biggest surprises have just been discovering what we had in terms of infrastructure and working around it to get the new equipment to fit,” said Westgaard.

But the biggest lesson Westgaard said he learned from guiding the start-up of a new facility had nothing to do with construction, high-tech features, or hiring issues. “For me, it was lead times,” he said. “When you’re trying to coordinate so many suppliers into a new facility—from batch plant equipment to mobile equipment and production equipment, to material fabrication to handling equipment outside to get your products loaded on trucks—you’re dealing with the full scope of every aspect of an operation,” he said. “It requires a lot of coordination and a lot of interfacing with many suppliers.”

Speaking two months prior to the grand opening, Westgaard still had several “major items” to put into place, particularly the plant’s yarding system. “But we’re breathing a lot easier now,” he said, “and by the time we hit our grand opening and open house, the plant should be functioning at a relatively high rate, and fully operational.”

In late 2015, the Ramsey plant will boost its capabilities by installing equipment that will allow the company to expand its selection of panel colors and textures. “At the moment our choices are relatively limited,” said Westgaard. “We’re starting with 12 ‘flavors,’ but we’ll soon be able to turn out another 21 and give our customers a full spectrum of options.”