Hollowcore planks are used predominantly for floor and roof deck components for various structures including multifamily housing, hotel and condominiums, office buildings, schools and prisons.
They typically are cast in widths of 2, 4 and 8 feet, although some precasters offer 10- and 12-ft widths. Six typical depths are used: 6, 8, 10, 12, 15 and 16 inches. Typical span-to-depth rations for floors range between 30 and 40, while for roofs they are 40 to 50.
Hollowcore planks typically are cast in 300- to 500-foot-long prestressing facilities with at least one system making the slabs in 60-foot-long self-stressing forms that circulate through a production cycle. The long-line method consists of a proprietary machine specific to the brand. It extrudes the concrete and creates the voids by means of either a rotating auger or by placement of aggregate filler that is later removed.
The general production method consists of 13 steps:
- preparing the form
- pulling strands from abutment to abutment
- stressing the strands to proper tension
- installing embeds and material to form openings if they occur
- making a pre-pour quality control check
- running the casting machine from end to end
- creating a 300- to 500-foot-long slab
- curing for 12 to 16 hours
- marking the lengths of specific pieces based on requirements for a particular project
- saw-cutting the individual pieces to length
- stripping the pieces
- making a post-pour quality control check
- moving the pieces to storage awaiting shipment to the site
The form side (bottom) is smooth as cast and typically remains that way in the finished construction. It is usually an exposed-to-view surface and is often painted. The top side also is usually smooth and can remain as such for direct carpet applications. It also can be kept slightly rough to receive a composite cast-in-place structural topping of 2 to 3 inches, as with double tees.
Producers of hollowcore planks use trademarked processes that create different shapes for the voids within the pieces. No benefits are derived from one format over another, although their processes may differ.
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