Last Friday I took a few hours from my normal schedule to attend a precast concrete plant tour. The opportunity was sponsored by the local chapter. It is always interesting to see how the products we specify are manufactured. Precast -SEIconcrete is particularly interesting to me, because they produce entire structural elements that enable lego-style modular construction.
Precast construction is extremely common in parking garages, but the technology can be applied to all types of construction. It is the standard in many European countries, because it enables quick on-site construction and reduces expensive field labor. The controlled process by which precast concrete is produced offers many potential benefits from quality control to sustainability. New precast products take advantage of the construction technique to embed wall insulation and finishes that allow concrete construction to approach the efficiency of stud wall construction. That’s good news for sustainability and design of homes in hurricane-prone regions.
The tour was offered by Dukane Precast, headquartered in Naperville, Illinois, a suburb just outside Chicago. They were eager to show off their newest state-of-the-art plant. It was constructed at the height of the building boom a few years ago but has since been running at minimal capacity.
Expecting continued industry growth Dukane made a special effort to develop a plant to maximize productivity, inspired by the assembly line concept. They call their design a circular system. A roller system allows the large concrete form tables to be shuffled around the facility in a circular pattern. At one stage, workers will add the rebar and inserts. Then the form is sent over the the prestressing position. Note that many precast concrete sections are pre-tensioned for structural performance and incidental shipping loads. The form proceeds through concrete placement, consolidation via shaking tables, curing compound application, and then to the temperature controlled curing room.
The massive forms are lifted into drying racks via a massive crane. They system is reminiscent of an automated car storage facility utilized in some dense urban areas. When operating at full capacity, our guide noted that they don’t have to heat the room, because so much heat energy is released by the curing concrete panels. When the elements have achieved enough strength they are retrieved from the curing racks and forwarded into the debonding room. Another crane hoists the panel from the form and a patented device flips the panels on their side for easier shipment. Dukane realized that flipping the panels on their end would allow shippers to avoid applying for wide load certifications when shipping the product.
If the ultimate job site is not yet ready to receive the finished panel, the factory can store a high volume of product in their yard. When developing the facility, Dukane experimented with a special ceramic product to serve as lightweight roofing. This ultimately proved unsuccessful, so, today, the open web roof joist remain uncovered, and the yard is open air. I have to admire the risk taking to evaluate an experimental product. The entire facility was apparently a proving ground for creative use of structural precast. The factory walls are comprised of standard double-tee beams. About two-thirds up, the webs are coped and an industrial crane rail is supported. The roof is the same double-tee section. The operations manager was very satisfied by the performance of the building. He emphasized the thermal mass of the concrete, which moderates the heat gain of the building over the day.
I really enjoyed the tour. It’s always nice to where the products, that we structural engineers specify, are produced. It was also encouraging to know that there are still engineers out there taking risks on their own property, hoping to further advance the construction industry. I would encourage all engineers to get out to the field or the fabrication plants as often as possible. It brings extra perspective to design decisions.