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Climbing formwork from Doka has reached full height at two huge liquefied natural gas (LNG) storage tanks being built on one of the largest construction sites in Texas. The first of the tanks is almost at its topping-out level of 122' wall height, while the second is just one lift of self-compacting concrete behind.
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High demand for natural gas has created a need for additional LNG storage across the USA. The US$ 1 Billion project at the Freeport receiving terminal and storage facility is being built by Technip USA in joint venture with Zachry Construction Corporation and Saipem SA. The two 270' (82.3 m) diameter tanks have been growing in tandem, with a third - and possibly fourth - following when they are complete.
The project uses some 54,000 sq ft (5,016m2) of Top 50 formwork plus 27,000 sq ft (2,508m2) of platforms from the MF 240 climbing system. Key to Doka's success in being chosen for the contract was its ability to pre-assemble the formwork.
Unlike competitors, Doka ensured that all the main operating platforms and gangs were delivered pre-assembled. Other systems would have needed the operating platforms to be put together on site. Pre-assembly reduced labor costs for the contractor as well as saving time and avoiding the need for crews to be trained in formwork assembly. The assembled formwork measures 16' by 16' (4.9 m by 4.9 m) and was delivered on trucks, which had to be escorted because of their width.
Complexity of the work has led to the storage tanks being built from self-compacting concrete (SCC). This enables full compaction to be achieved without the need for any vibration and has proved a major advantage on the tanks. High 14.5' (4.4 m) pours, heavy reinforcement and extensive post-tensioning ducts would have made it very difficult to achieve the high quality needed using conventional methods.
The SCC mix includes a super plasticizer and stabilizer to make it flow more easily, with the result that its own weight is sufficient to compact it into every part of the formwork. As well as speeding the construction process, its use spares workers from the risks and discomfort of vibration. Site noise is also reduced.
Production of SCC is more demanding than regular concrete, as it requires greater control over aspects such as the consistency, water control and logistics. Zachry has opted to batch the concrete on site – particularly as the remote location would have made external supply too unreliable. The tanks are being built on Quintana Island, some two hours from the nearest town of any size.
Considerable resources are needed to ensure smooth and rapid construction of the huge tanks. Each 14.5' (4.4 m) lift takes some 10 hours. A fleet of 18 concrete trucks has been assembled to ensure that the four 62m pump trucks are kept supplied throughout the operation – essential for SCC.
Three tower cranes serve each tank. The entire ring of Top 50 gangs and MF 240 platforms is raised by crane for each lift and, thanks to the 448 MF 240 brackets, none of it will need to touch the ground until the last pour is complete. "It makes my job easier when you provide a system that does it all," says Superintendent Augustin Sanchez.
Doka’s services included the preparation of engineering and field use drawings and assistance on site by a competent field service technician during the initial formwork installation and completion of the first two lifts. The contractor has praised this on-site instruction and advisory service, which has helped ensure efficient use of the Top 50 and MF 240 system.
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