Trade Journals for the Concrete Industry

For more than 20 years, Tindall Corporation’s Utility division – now Tindall Infrastructure Group – grew side-by-side in the same facility as the firm’s South Carolina prestressed division, until it was literally bursting at the seams. “It became overcrowded and began to hinder our growth potential,” explains Joel Sheets, senior vice president of operations for the newly named Infrastructure Group. While ACT/Wiggert plants are pre-tested, pre-plumbed and wired at the Wiggert factory in Germany, site assembly is generally overseen by an ACT engineer; however, this was not possible due to COVID in the summer and fall of 2020 when the batch plant components were delivered to the new site (fig 5). Strict travel restrictions severely limited personal contact. The Infrastructure Group staff had to assemble much of the batch plant with remote instructions and video call guidance from ACT engineers. “We ended up having our in-house electrician do a lot of the electrical work, since the ACT engineers couldn’t get here due to travel restrictions,” Sheets notes. “It was challenging but, unfortunately, it was the way of the world at that time. By the time ACT was able to dispatch a technician, we had started to turn the corner making real progress.” The ACT/Wiggert batch plant is centrally located (fig 6) in order to efficiently feed all three production areas via a dedicated conveyor to the Prima automated line, and via an auto- mated ACT/Wiggert rail transport cart that carries two 4-yd3 crane buckets to the plant’s two custom and specialty precast bays. Tindall DIY helps speed construction Throughout the new Infrastructure Group plant, Tindall precast products helped keep costs down and accelerate the pace of plant construction. Modular prestressed concrete wall panels were used throughout the 128,000 ft2 facility. Huge three-chamber Tindall precast box culverts were stacked on top of each other (fig 7) and end-to-end to form a 40-foot high by 80-foot long (~12x24 m) six-bin aggregate storage system with a total storage capacity of 21,600 ft3 (~612 m3) or approximately 1,080 tons. For precise fast/slow aggregate batching, ACT/Wiggert-provided galvanized steel cones with dual batching gates which were attached to the bottom of each of the six concrete bunker bins. Tindall also precast a below-ground truck dump station where aggregate deliveries are unloaded directly from the truck and transported automatically via a 233-ft (~71 m) long conveyor to the appropriate storage bin inside the facility (fig 8). Indoor aggregate storage means aggregate is protected from the weather ensuring consistent moisture and temperature control for best practice in producing consistent high quality concrete. “By automating our aggregate loading and increasing the capacity of our storage bins, we have been able to reassign the driver who previously worked full-time to keep our old aggregate bins full,” Sheets notes. “The rail cart inside the plant with its two crane buckets (fig 9) has also eliminated the need for a full-time fork truck driver. Every aspect of the new plant is designed for efficiency, quality and safety.” An ACT/Wiggert weigh belt runs underneath the aggregate bins inside a Tindall precast concrete tunnel that supports the aggregate bins above. Each of the six aggregate bins are equipped with either an ACT/Wiggert Hydrotester II or Po- larmatic PolarmoistTM sensor for real time moisture reading correction and measurement comparison. Moisture information from the aggregate probes and the moisture probe in the ACT/Wiggert HPGM planetary mixer floor is used by the ACT/Wiggert WCS concrete batch control system, which operates on a Microsoft Windows 10 computer platform (fig 10). The ACT/Wiggert Hydromat water dosing system uses all moisture information to accurately and automatically achieve the correct water/cement ratio which is critical for reliable SCC concrete production. The WCS controls also automatically track and store copious amounts of data throughout the mixing and batching process allowing for measurable improvements throughout the system. The system performs precise batch sequencing, records and reports on recipes, batches, inventory, maintenance, and all other production statistics critical to business operations. Two 700 BBL (2,800 ft3/~79 m3) double-walled split cement silos provide storage for Portland Type III cement, fly ash and milled limestone filler. ACT/Wiggert provided an admixture weight-based metering system that can handle up to eight different admixtures. Tindall’s Infrastructure Group currently uses three to four admixtures, but has the flexibility to add more if needed. A weight-based admixture metering system was chosen because admixtures are becoming more concentrated, requiring less admix and more precise metering. The weigh belt (fig 11) below the aggregate storage bins empties into a high speed skip hoist (fig 12) that lifts each load of dry ingredients to the mixer. By prebatching into the skip hoist, there is never a delay in mixer loading, ensuring the quickest batch cycle time and maximum production. The ACT/Wiggert HPGM planetary mixer can produce a new batch every three minutes due to its optimal mixing efficiency. Powerful mixing stars rotate around a center axis to deliver intense countercurrent mixing energy directly to the concrete. This energy transfer is essential for high performance concrete such as the SCC used throughout the Tindall plant. Two 4.0 yd3 concrete holding hoppers are located below the mixer platform where finished batches can be staged allowing the mixer to begin mixing the next batch immediately, eliminating wait times. First full year of operation By the end of 2021, the new Tindall plant had been in operation for about six months and was already seeing the benefits of its automation and data-driven strategy. “Cycle times have improved tremendously,” Sheets explains. “Our batch plant can keep up with all our demands with ease. We have two 4.0 yd3 holding hoppers – one for the Prima line and one for the custom and specialty bays supplied by the traveling cart.” A crane operator on the Prima line (fig 13) calls for each new batch as needed. Each Prima mold moves on its own traveling pallet from station to station, so that workers remain in one position and specialize in one task, such as demolding, cleaning, setting up new molds, and curing. Worker efficiency is optimized and safety is enhanced. A second crane operator works the other two production bays devoted to custom and specialized utility products. The two 4.0 yd3 crane buckets automatically travel to the bays as needed from the mixer platform on an ACT/Wiggert rail cart. The cart is equipped with sensors to detect any obstruction on the line and automatically stop the cart thereby ensuring safety. The crane operator never has to wait for mix to be delivered. The new Tindall plant recently added a second shift. Accord- ing to Sheets, the Tindall Infrastructure Group previously produced about 120 yd3 (~92 m3) per day at its old plant. Currently, the new plant produces about 200 yd3 (~153 m3) per day with a single shift and up to 350 yd3 (~268 m3) per day with a second shift (fig 14). The Infrastructure Group has added about 20 new jobs since moving to the new location, primarily in for adding a second shift, bringing its head count to about 100. Data from Tindall’s new ACT/Wiggert WCS batching control computer is being integrated with the plant’s ERP system. “We are an industrially engineered company and use every bit of information to help improve our operation and achieve the greatest efficiency, quality and safety,” Sheets emphasizes. “Every aspect of our operation has been improved. Consistent SCC mix is allowing us to pour without the need for vibration and pour faster than ever. The quality we get from our new wet casting process provides the highest possible quality – a smooth finish with no bug holes or other defects.” High compressive strength is a requirement for all precast utility products and those from Tindall’s Infrastructure Group are no exception (fig 15). “Our mix design goal is 6,000 PSI (~41.4 MPa), but we regularly hit 7,500 (~51.7 MPa) with our new plant,” Sheets notes. “That means we can demold and move product with confidence because our early strength is so high. Everything helps to improve efficiency, output and quality.” There is no limit to the types of products or capacity of the new Tindall Infrastructure Group plant (fig 16). The plant is able to produce a full range of precast utility products, from curb inlets, multipurpose boxes, storm structure hole bases, vaults, trench components, T-series bases, sanitary sewer cast inverts, bases, risers, cones, tops, stormwater retention systems, cisterns, plenums, and packaged systems such as sew- age pumping stations, backflow preventors and meter vaults. Tindall provides complete engineering and design services to help customers meet even the most demanding project goals. The $28 million Infrastructure Group plant is the firm’s largest investment since dedicating a new precast prestressed Mississippi Division plant in Moss Point to replace its previous plant in Biloxi, Mississippi, which was badly damaged by Hurricane Katrina in 2005. “We believe we will see strong growth during 2022 (fig 17). Everything about our new plant is designed to optimize work flow, increase our capacity, improve quality and ensure safety.” Ten bridge cranes with 35-ft (~10.7 m) hook heights enable the new plant to produce utility structures that were not possible in the past. “For instance, we bought molds for full 11-ft (~3.4 m) high stair units that we had to pour in sections at our old plant. Now, we can produce a single full-size unit that can be installed as one module. We now have the space and mixer capacity to accommodate continued growth with new molds which we have already ordered.”