Missouri Cement Plant

16 Days and Whataya Get?
First 2 Silos in Green Project

by Pamela Dittmer McKuen

Along the banks of the Mississippi River and surrounded by acres of forest, an immense cement manufacturing plant is unfolding. When completed in mid-2009, it will be the world's largest single-kiln facility, producing about 4 million metric tons of cement each year.

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Holcim (US) Inc., based in Waltham, Mass., is building the plant on 3,900 acres in St. Genevieve Co., about 50 mi south of St. Louis, at a cost of $905 million. The company says the plant design is one of the most sophisticated in the cement industry today and at the same time is environmentally sensitive.

The location, an existing quarry, was chosen for numerous reasons, one being that it contains high quality limestone, the key ingredient in cement. It also has an estimated quarry life of more than 100 years. The plant will have its own harbor, from which 90% of its products and materials will be shipped and received. Water transportation is perhaps the most environmentally, economically and energy-efficient means of transport available.

Holcim's land reclamation plan includes quarrying a maximum of 200 acres at one time and preserving more than 2,000 acres of its site as a conservation buffer area.

Cement production requires intensive use of raw materials and emissions to the atmosphere, the most significant being carbon dioxide. The company is reducing its demand for natural resources and its CO2 emissions by replacing fossil fuels and raw materials with waste and industrial byproducts. Heat recovered from the kiln and clinker cooler is recycled for preheating the raw meal, reducing thermal energy consumption.

Holcim's emissions limits will be among the lowest in the world, according to the company.

The plant's two-story, concrete tilt-up office building, designed and built by
The Korte Co. of Highland, Ill., will be a certified green building in accordance with the LEED rating system of the U.S. Green Building Council.
Groundbreaking took place in March 2006, and Bloomsdale Excavating Co. of Bloomsdale, Mo., has been readying the office site, a year-long endeavor.

13 Silos Coming

Limestone is usually quarried using blasting and drilling techniques. It is crushed, combined with clay, dried and preheated, then kiln-baked at temperatures of 2,000 degrees or higher.

The superheated mixture forms gravel-sized pieces called clinker. The clinker is rapidly cooled and ground into a fine powder along with a small amount of basic gypsum to become cement.

The first two of 13 slip-form silos were completed in December in a design-build joint venture between St. Louis-based MC Industrial and Hopkins, Minn.-based T.E. Ibberson Co., a world leader in slip-form technology. The silos perform varying storage functions, depending on where they are stationed in the manufacturing process. Slip-form refers to a continuous pouring of the concrete shell, a technique that eliminates seams and reduces structural vulnerabilities.

"It's pretty much the most effective way to build storage silos," says project manager Will Chipley of MC Industrial, a subsidiary of St. Louis-based McCarthy Building Cos. "Slip-forming is basically the only way to get a monolithic structure so there are no cold joints. Anywhere there's a cold joint, you've got a potential weak point where the product can leak out or water can seep in."

The trick is, once the pouring begins, it cannot be stopped. The work must continue round-the-clock until it is finished because it is wet, and a continuous pour will prevent seams from forming.

The first two silos are raw meal silos that hold crushed limestone and other ingredients before they go to the kiln. Measuring 60 ft in diameter and 275 ft in height, they were constructed with more than 6,000 cu yds of cement poured during 16 consecutive days by 85 workers on 12-hour shifts.

Next up are the two clinker silos, said to be the world's largest at 150 ft in diameter and 207 ft high, Chipley says. Clinker is a gravel-like intermediate product that will later be crushed to make the cement. The forms and decking were built over the winter, a six- to eight-week project and the silos poured in the spring.

After that will come two groups of four cement-storage silos, 275 ft high and 79 ft in diameter. These are designed with inverted-cone bottoms and will hoist the cement perhaps 100 ft above the ground.

A 13th silo, 207 ft high and 40 ft in diameter, will hold reject material. By the time it is finished, the silo team will have poured 90,000 cu yds of concrete.

"You need discharge equipment and conveyers below the bottom of the material," Chipley says. "Instead of trying to go underground-they are sitting on a bed of rock, we're making low points along the exterior walls and letting gravity do some of the discharge work."

A Concrete Cone

If the cone is pointed downward, the cement, which is denser than flour, has a tendency to clog, he says.

Construction of the cones is another engineering marvel. The technology is relatively new, and the size of the silos is enormous.

First, the silos are slip-formed. Then 24 precast, pie-shaped wedges, 80 ft in diameter and 70 ft long, weighing about 30 tons each, are hoisted over the top. With outer edges resting on an interior ledge circling the silo 60 ft above grade, the wedges are arranged to form an upside-down cone and held in place with giant tendon rods. Concrete is poured over the structure to form a solid piece.

"For a week or more, these things are kind of floating in space, supported by temporary rigging," Chipley says. "The slip-forming is easy compared to that."

Holcim's parent is Holcim Ltd. of Zurich, Switzerland. The company has 14 manufacturing plants and 70 distribution terminals in the United States and ships more than 15 million tons of cement and related materials a year. The new plant, the company's second in Missouri, is expected to be operational mid-2009 and will produce about 4 million tons of cement annually.

"What this means for the building industry in the United States is it lessens our need to import cement," Chipley says.

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