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Hollowcore Slab Systems

     A hollowcore slab is a precast, prestressed concrete member with continuous voids provided to reduce weight and, therefore, cost and, as a side benefit, to use for concealed electrical or mechanical runs. Primarily used as floor or roof deck systems, hollowcore slabs also have applications as wall panels, spandrel members and bridge deck units.

     An understanding of the methods used to manufacture hollowcore slabs will aid in the special considerations sometimes required in the use of hollowcore slabs. hollowcore slabs are cast using various methods in the seven major systems available today. Because each production system is patented, producers are usually set up on a franchise or license basis using the background, knowledge and expertise provided with the machine development. Each producer then has the technical support of a large network of associated producers.

     Two basic manufacturing methods are currently in use for the production of hollowcore slabs. One is a dry cast or extrusion system where a very low slump concrete is forced through the machine. The cores are formed with augers or tubes with the concrete being compacted around the cores. The second system uses a higher slump concrete. Sides are formed either with stationary, fixed forms or with forms attached to the machine with the sides being slip formed. The cores in the normal slump, or wet cast, systems are formed with either lightweight aggregate fed through tubes attached to the casting machine, pneumatic tubes anchored in a fixed form or long tubes attached to the casting machine which slip form the cores.

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