Codes for designing prestressed concrete structures provide high levels of corrosion resistance that result in economical, durable systems. Epoxy-coated prestressing strands can provide the needed corrosion resistance. While most prestressed concrete structures will not require epoxy-coated strand, structures exposed to aggressive corrosion conditions may benefit when epoxy-coated strand is used. Epoxy-coated strand is 7-wire prestressing strand with a 25- to 45-mil organic coating.
Elongation for coated strand may be calculated in the same manner as for uncoated strand using the load-elongation data supplied by the manufacturer. Manufacturers recommend that the stress-relaxation component of the losses be figured by doubling the relaxation loss calculated for uncoated strand. Tests on epoxy-coated strand samples provided these results: detentioning of epoxy-coated strands should be performed at less than 160 Farenheit degrees; bond could be lost at temperatures greater than 165 Farenheit degrees.
For installation and stressing, bite-through wedges specifically made for use with epoxy-coated strand should be specified. Chucks designed for uncoated strand should not be used. Because the overall diameter of epoxy-coated strand is 50 to 90 mils greater than uncoated strand, it may be necessary to enlarge the holes in the stressing abutment. For external post-tensioning systems, where the tendons are located on the outside of the member, avoid sharp curves in the tendon path. Where tendons pass over a deviation point, it may be necessary to provide cushioning material to avoid abrasion of the epoxy coating.