LEHIGH PORTLAND CEMENT PLANT EXPANSION – Mason City, Iowa

Clinker is an intermediate stage in cement making. Raw materials are ground, then fused in a horizontal rotating kiln at temperatures exceeding 2,300 ° F. After clinker is discharged from the kiln, it is normally stored for later grinding. Ultimately, the rock-like nodules are ground, along with additives, into a fine power to produce Portland cement.

Resembling a nuclear containment building, the 200’ tall, 120’ diameter clinker storage structure was designed to handle 65,000 tons of hot clinker having as much as a 300^oF temperature differential with the outside air. Densely placed reinforcing steel, 6,000 PSI concrete, slip-forming, post-tensioning, three transfer towers, and the installation of 550 feet of conveyors were key elements in the construction of this new "River City" landmark.

Heidelberger Zement, of Heidelberg Germany holds a major interest in Lehigh. To match Heidelberger’s other facilities, the exotic structure was designed in Germany while meeting the requirements of an unique section of the American Concrete Institute "Manual of Standard Practice.

As the design progressed, Downing and the rest of the construction and project management team developed an excellent working relationship with Heidelberger Zement’s designer based in Stuttgart. By visiting Heidelberger’s other operating facilities in Germany, then re-working the design in Stuttgart, Downing was able to work with the designer to convert certain design elements to a better match-up with construction practices more economical in the U.S.

Later, Downing initiated an innovative approach to the roof design. On site, to overcome congestion, a 250 ton crane, with 200’ of tower and a 105’ boom, became the workhorse of the full-time hoisting challenge. Teaming up with a local structural engineer and the German designer, the construction team was able to redesign the roof to take advantage of larger lifting equipment available on site. By creating a self-supporting, composite structural system, the savings in labor and construction equipment shaved 2% off the total construction budget.

Slipforming a structure of this size takes as much art as science. Continuously in motion, this slip took 11 days to complete. Working at three levels, inside and out, crews of laborers, carpenters, cement finishers, ironworkers, and operators placed concrete, rebar, and post-tensioning conduits, raising the form at 10" an hour, 24 hours a day.

Iowa’s winter threatened the temperature sensitive post-tensioning process with - 60^oF wind chills. Another site innovation involved devising an internal heating system for the silo that allowed the horizontal conduit runs to remain above 32 ^oF, warm enough to allow the successful completion of grouting for the post-tensioned tendons.

And, when the National Presidents of the Operating Engineers and Iron Workers couldn’t solve their local’s jurisdictional disputes, construction staff resolved the issues on site. When the post-tensioning subcontractor was unable to proceed with its work, site staff took over and completed the post-tensioning, keeping the project moving and putting it back on schedule.