Dual direction pre-stressed pre-tensioned precast concrete slabs and process for same
A precast roadway slab is pre-tensioned longitudinally and transversely, and may also be post-tensioned. A casting bed has the capability of permitting pre-tensioning of a concrete cast to be carried out within the casting bed in both the longitudinal direction and in the transverse direction. Slots are provided at regular intervals within the side walls and jacking heads of the casting bed for tensioning wires to pass therethrough for pre-tensioning. The process utilizes a multilayer grid of pre-tensioning wires disposed within the casting bed, prior to pouring of the concrete. The cast concrete product can also be made with optional tubular ducts, laid parallel to the longitudinal wires, for post-tensioning subsequent to the cast of the concrete. The post-tensioning of the hardened cast, if called for, takes place at the job site.
1. A precast roadway slab which comprises
(i) a one piece casting of concrete,
(ii) a plurality of spaced, first pre-tensioning elements extending in a longitudinal direction of the slab at a first elevation thereof, the first pre-tensioning elements being bonded to the concrete and in a detensioned state, and
(iii) a plurality of spaced, second pre-tensioning elements extending in a direction substantially perpendicular to the longitudinal direction of the slab, the second pre-tensioning elements being (a) bonded to the concrete and in a detensioned state and (b) located at a second elevation of the slab that is spaced above the first elevation, and at a third elevation of the slab that is spaced below the first elevation,
said concrete having a compressive force transferred thereto by said bonding of said detensioned first and second pre-tensioning elements to said concrete.
2. The precast roadway slab according to claim 1 , further comprising a plurality of spaced ducts disposed within the slab, the plurality of spaced ducts being configured to receive therein a corresponding plurality of post-tensioning elements.
3. The precast roadway slab of claim 2 , wherein a plurality of the spaced ducts extend in the longitudinal direction of the slab, and a plurality of the spaced ducts extend in the direction substantially perpendicular to the longitudinal direction of the slab.
4. The precast roadway slab according to claim 3 , wherein the plurality of the spaced ducts extending in the longitudinal direction of the slab are at the first elevation.
5. A precast slab comprising:
(i) a casting of concrete;
(ii) a plurality of spaced, first pre-tensioning elements extending in a longitudinal direction of the slab at a first elevation thereof, the first pre-tensioning elements being bonded to the concrete and in a detensioned state; and
(iii) a plurality of spaced, second pre-tensioning elements extending in a direction substantially perpendicular to the longitudinal direction of the slab, the second pre-tensioning elements being (a) bonded to the concrete and in a detensioned state and (b) located at a second elevation of the slab that is spaced above the first elevation, and at a third elevation of the slab that is spaced below the first elevation,
said casting including therein a first compressive force in the longitudinal direction of the slab, the first compressive force being associated with the bonded and detensioned first pre-tensioning elements, and a second compressive force in the direction substantially perpendicular to the longitudinal direction of the slab, the second compressive force being associated with the bonded and detensioned second pre-tensioning elements.
6. The precast slab according to claim 5 , wherein the first compressive force and the second compressive force are forces transferred by static friction from the bonded and detensioned first and second pre-tensioning elements to the casting of concrete.
7. The precast slab according to claim 5 , wherein each of the first and second pre-tensioning elements is a metal, multi-strand wire.
8. The precast slab according to claim 5 , further comprising a plurality of spaced ducts extending in the longitudinal direction of the slab, and a plurality of spaced ducts extending in the direction substantially perpendicular to the longitudinal direction of the slab, the plurality of spaced ducts being configured to receive therein a corresponding plurality of post-tensioning elements.
9. The precast slab according to claim 8 , wherein each of the plurality of spaced ducts is configured as an elongated slot to facilitate placement of the post-tensioning element therein.