As a result of increased cement demand in the construction industry, Lehigh Cement decided to expand its cement facility in Union Bridge, Maryland. Part of this expansion included a post-tensioned cement clinker silo approximately 122 ft. in height and 148 ft. in diameter.

Post-tensioning the silo in the horizontal or hoop direction was selected as the most efficient reinforcement system. The post-tensioning ducts and anchorages were placed during the slipforming operations. The strands were placed in the ducts, stressed, and grouted after the slipforming operations were completed. As a result of the primary reinforcement being placed after the slipforming operations were completed, less labor was required on the critical path, and an increased production rate was achieved. Additionally, more accurate placement of the reinforcement was achieved due to improved control of the operations. Placement and consolidation of the concrete was simplified due to less mild reinforcement congestion. Proper concrete placement was vital to the performance and durability of the structure. Safety was improved since there were fewer workers on the suspended platforms. Thin members were achieved with post-tensioning - reducing material and labor costs, and increasing the speed of construction.

The hoop post-tensioning allowed for the control of concrete stresses to levels below the cracking limit. Therefore, long-term performance and durability is enhanced and maintenance costs reduced. The post-tensioned walls are well-suited to tolerating overloading conditions due to the positive anchoring of the tendons at the pilasters as compared to mild reinforcement lap splices that are located throughout the structure.

Post-tensioning has proven to be an economical alternate to conventional reinforcement for large-diameter silos.