Eco Electrica, an electical generation company located outside of Ponce, Puerto Rico, planned to switch from a propane gas energy source to Liquefied Natural Gas (LNG). An important feature in their plan included the construction of the LNG storage tanks. Pitt-Des Moines (PDM), a leading expert in the design of tank systems in use throughout the world, was contracted with Aireko Construction to build what would be the world’s largest LNG tanks. Although the tank itself is metal, 2' thick posttensioned concrete walls enclose the tanks to protect against leakage.

This massive concrete construction project presented several unusual forming conditions. The concrete tank enclosure required easy access for vertical and horizontal post-tensioning devices during forming operations. In addition, unpredictable weather over the months of construction meant that it must be designed to withstand hurricane-force winds.

The Flex-Form system was chosen because it is shipped to the job site with rolled ribs for the proper inside radius and outside radius already installed and because of the smooth concrete finish that the steel form face provides. Mounted on a jump form system for simple lifting by crane, the rollback feature allowed workers adequate access for rebar installation and post-tensioning operations. In addition, the assembled components met the hurricane resistance requirements.

Project Engineer Luis Uzcategui directed the Aireko construction crew to set the first 6' of forms all the way around the circular structure. Once that pour was completed, they added a row of 4' forms so that subsequent lifts would build 9' of wall with a 1' overlap of the previous pour.

Workers appreciated the walkway and the easy access for the installation of rebar, imbeds and post-tensioning tubes. PDM and Aireko officials commented on the safety advantages and convenience of the wide working platform.

Despite delays caused by threatening weather, the contractor finished the enclosure on time and within the budget. They reported that the average 8 day pour cycle was extraordinary for a structure of this size.

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