Originally constructed in the mid 1970's, the 21-foot-diameter siphons of the Central Arizona Project carry Colorado River water into the arid regions of central Arizona. The siphons are built of precast concrete, externally prestressed with spiral-wrapped wire and covered with shotcrete.

In early 1990, workers discovered substantial corrosion of the original bare prestressing wire in two siphons, accompanied by cracking of the concrete. A repair contract was subsequently awarded by the United States Bureau of Reclamation.

The repair design consisted of removing the earth cover, shotcrete and corroded wires and replacing the damaged wires with 0.6 inch diameter VSL monostrands. The monostrands are individually epoxy coated, greased, and extruded in 100 mil thick polyethylene sheaths. In addition to supplying the post-tensioning strand for this unique application, VSL also developed special anchorages and wedges for the circumferential post-tensioning.