11 October 2011
11 October 2011
A spiral staircase inside the Texas A&M University Health Science Centre has been made using a fibre-reinforced polymer (FRP) composite that MFG Construction Products (MFG-CP) made into forms giving the concrete its structure and aesthetics.
According to AOC, the architectural design required three forms, one for each floor. At the site, concrete was poured into the forms which remained in place until the concrete cured.
AOC say a design feature was engineered into the form so that the top riser could accommodate an overlaid marble cover that matched the surface of the floor at the top. In addition, MFG-CP engineered a solution on site that allowed one form to be modified so it could form the staircase around an already-installed large column.
Before the composite forms could be made, MFG-CP explain that they used engineering drawings to create pre-construction replicas of finished stairway sections out of wood and masonite. The replicas served as precise dimensional models for building the FRP forms that would give the poured concrete its final shape.
To keep the FRP forms from adhering when removed from the model, MFG-CP say they coated the surface of the model with a special wax. Workers then apply the first layer of the form itself – a sandable gel coat that will create the finished surface of the concrete. Then a structural laminate was applied to keep the form rigid for shipping, on-site handling and the pour and cure cycles. The laminate is formed by lay-up of resin-impregnated glass fibre mat and woven roving.
AOC say that to achieve the required rigidity, select areas of the laminate are internally cored with balsa wood and externally braced with hardwood pieces. The coring and braces are encapsulated into the laminate to result in a monolithic unit when the resin reactively cures into a cross linked solid.
The resin MFG-CP used to mould the forms was Altek H864, which AOC explain is their low-shrink unsaturated polyester. MFG-CP Sales ManagerJim Williams pointed out characteristics of the resin that contributed to the laminate's strength and physical integrity. "This is a very good all around resin that wets the glass fibres well and rolls out easily," Williams said. "And by showing very little entrapment of air, Altek H864 also ensures a more solid laminate construction."
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