DYWIDAG Circular Structure Repair with Hoop Tendons
1. Scope
This specification is for hoop tendons of corrosion protected 7-wire strand, high tensile strength prestressing steel used to repair PCCP pipe. The hoop tendons shall be extrusion coated strand with polypropylene, as manufactured by DYWIDAG-Systems International, or an approved equal.
2. Material
The material used to manufacture the strand shall be as follows:
Prestress Strand
Steel strand shall be 0.6 inch (15.2 mm) diameter 7-wire prestressing strand. If standard prestress strand with round wires is used, the strand shall meet ASTM A 416 with an ultimate stress of 270 ksi. If made with drawn and compacted wires, the strand shall meet ASTM A 779 or British Standard BS 5896-“Specification for High Tensile Steel Wire and Strand for the Prestressing of Concrete.” The compacted strand steel should have a nominal tensile strength of 1820 N/mm and a characteristic breaking load of 300 kN.
Corrosion Inhibitor
The organic corrosion inhibitor shall be Visconorust 2889 or equivalent, (which surpasses the corrosion inhibitor standard in ACI Bldg. Code 318, Sec. 18.14.3, and the specification for “Unbonded Single Strand Tendons”, revised July 1993 by the Post-Tensioning Institute.) The corrosion inhibitor shall have a:
- Melting point of over 260°C
- High Reserve Alkalinity of 170 or greater for extended neutralization properties for long term corrosion protection
- Minimum Specific Gravity of 1.04 (which is greater than water’s 1.0) to increase resistance to moisture encroachment
- Salt Fog Accelerated Corrosion Test, exceeding 1500 hrs., per ASTM B-117, 5 mils
- High resistance to microbiological and fungi degradation
Polymer
Polymer sheathing used for extrusion coating of the strand shall be minimum 80 mils nominal polypropylene (cell classification PP 210 B55542, as defined by ASTM D-4101 or approved equal).
3. Corrosion Protection
Corrosion protection shall be as follows:
The unbonded tendons strand shall be fully coated by corrosion inhibitor and then encapsulated by a seamless polypropylene sheath.
Corrosion inhibitor shall fill all space between strand wires and between the strand and the extruded sheath. The diameter of the corrosion inhibitor film covering the strand shall be 0.005 to 0.010 inches greater than the diameter of the bare strand.
The strand sheath shall have a wall thickness of a nominal 80 mils or 0.08 inches. This sheath shall be hot-melt extruded over the corrosion inhibitor encased strand.
4. Quality Control
Manufacturer of the seamless extrusion coated strand shall certify that the requirements of this specification have been satisfied.
Field inspection shall verify the following:
- Full coating with corrosion inhibitor. Determine smoothness of extruded sheath by visual inspection. Reject if the sheath external surface follows the helical lay of the strand wires.
- Minimum wall thickness of sheath. Reject if outside diameter of extruded sheath is less than diameter of bare prestressing strand plus 0.010 inches plus two times the specified wall thickness.
- Integrity of the sheath. Inspect for presence of corrosion inhibitor that would be visible at a sheath hole, puncture or laceration, since the internal corrosion inhibitor is under a slight positive pressure. Remove corrosion inhibitor and examine sheath damage. Repair sheath in accordance with the recommendation of the manufacturer.