When most people think of Wisconsin, they picture dairy farms, cheese production, and, of course, beer making. They probably don't picture sand processing facilities, but that's exactly what they would find in the northwestern part of the state.

Many companies are continuously looking for good sources of silica sand, and Wisconsin has the distinction of having some excellent pockets of this precious resource. After various processing steps, the resulting high-purity product is used in many applications, including glassmaking, metal casting, paints and coatings, ceramics, and water filtration. It also is in especially high demand in the oil and natural gas drilling industry.

The considerable sand processing required to reduce impurities involves huge storage, classifying, and drying silos. Concrete is the ideal material for these silos' massive foundations.

By any measure, the production and placement logistics required to construct a huge concrete slab at the Chippewa Falls sand plant in northwestern Wisconsin were challenging. For 12 hours, the trucks kept coming, turning one after another into the sand processing facility located just north of Chippewa Falls. Trucks from almost every ready-mix producer in the area participated on the job, and even they were not enough. Companies as far away as the Twin Cities sent trucks.

Measuring 168,939 cubic feet and holding more than 800 tons of steel reinforcement, the slab will support 12 silos, each 70 feet high and 48 feet in diameter. Placing the required quantity of concrete for such a large slab within 12 hours would require five batch plants and almost 100 trucks. Meeting these supply challenges was compounded by the approaching harsh Wisconsin winter.

Soil stabilization

Construction of the base slab hit an early roadblock. Site engineers Krech Ojard & Associates and excavator/producer Haas Sons discovered that the very properties that make for good silica sand can make for very poor compaction, especially for a foundation weighing more than 10,000 tons and supporting even greater weights. Several options were considered and turned down due to time constraints.

Haas Sons contacted their cement supplier, Lafarge North America, which designed an initial lean mix solution for meeting the specific objectives of this soil stabilization application. The low-strength, coarse aggregate mix is similar to flowable fill, but this project demanded more stability.

After some fine tuning by the project engineers to slightly increase cement quantities, the final lean mix used was 66% Class C fly ash (250 pounds), 33% Type I/II portland cement (125 pounds), 50-50% rock to sand and 46 gallons of water with air at 9-10% and 8-inch slump. Compressive strengths of 400 psi were required to support the monolithic foundation slab.

Haas Sons' ready-mix plants in Eau Claire and Thorp supplied 14,500 cubic yards and A-1 Redi Mix produced the balance. On the last day, R&S Pumping Service topped off the mat with Lewis Construction's 240 Somero Laser Screed. “We poured the mix very wet so it was very easy to place,” says Gary Haas of Haas Sons.

Among the lessons learned at this point was that the lean fill worked well and that a single supplier in this small market would not be able to supply the quantities required for the monolithic placement.

Slab placement

Where in a town of 13,540 do you get enough ready-mix concrete for a job requiring placing 6253 cubic yards of 4500 psi concrete into a 4-foot-deep footing pad in less than 12 hours?

After several meetings that were spearheaded by concrete contractor Steve Lewis of Lewis Construction, facilitated by the general contractor Tom Hubbard of Cedar Falls Building Systems, and coordinated by Lafarge, a team of three ready mix producers—Haas Sons, A1 Redi Mix Concrete, and American Materials—came together to work on the project. They, in turn, rented additional trucks from other ready-mix companies.

Supplying a steady stream of this much concrete required five batch plants belonging to the three ready-mix producers—Haas Sons' plants in Eau Claire and Thorp, Wis.; A-1 Redi Mix Concrete's mega plant in Eau Claire; and American Materials' plants in Eau Claire and Menomonie, Wis.—and 96 concrete trucks supplied by 10 ready-mix producers.

Lafarge calculated the amounts and delivery times required. Haas Sons committed to producing 200 yards per hour, A1 committed to 150 yards, and American Materials committed to 200 yards.