Overview
ISO 14655:1999 defines requirements for fusion-bonded epoxy-coated and epoxy-coated & filled seven-wire prestressing strand used in the prestressing of concrete. It covers materials, surface preparation, coating application, minimum coating performance, testing methods (including holiday detection, adhesion and pull‑out tests), handling, identification and manufacturer certification. The standard is focussed on corrosion-protective coatings for prestressing steel and includes normative test methods in Annex A and material requirements in Annex B.
Key topics and technical requirements
- Scope: Fusion-bonded epoxy powder coatings for seven‑wire prestressing strand; coated and filled variants (voids between wires filled with epoxy) are included. Note: use in pre‑tensioned, fire‑rated applications should be approached with caution.
- Materials: Strand must comply with ISO 6934‑4 (or purchaser‑specified product standard). Epoxy powder and sealing materials must meet annex requirements and be certified by the supplier.
- Coating application & timing: Surface must be cleaned and coated promptly - no more than 10 minutes after cleaning. Coating is applied by electrostatic deposition and cured per powder manufacturer instructions; surface temperature monitoring is required.
- Coating thickness:
- Coated strand: nominal 650 μm – 1 150 μm (less than 650 μm possible by agreement with supporting test data).
- Coated & filled strand: 400 μm – 900 μm.
- Mechanical performance:
- Must meet strand tensile/elongation properties of ISO 6934‑4 or purchaser spec.
- Relaxation loss: ≤ 4% after 1 000 h at 70% specified max force (coated); ≤ 6.5% for coated & filled.
- Coating continuity & holidays: Continuous holiday detection required; acceptance limit is no more than two holidays per 30 m (more leads to rejection).
- Adhesion tests: Bend test (180° around mandrel = 32× strand diameter) and tensile testing at 23 ± 2 °C; no visible cracking up to 1% elongation.
- Bond: Grit‑impregnated strand requires pull‑out testing (frequency: typically once every 15 000 m) to verify bond strength.
- Temperature sensitivity: coating must tolerate 66 °C without reduced bond; softening begins above 74 °C, and bond transfer is effectively lost near 93 °C.
- Handling & repair: Damage repair with manufacturer‑recommended sealing material; repaired areas must meet minimum thickness and rust removal procedures.
Applications and users
ISO 14655 is applied where corrosion protection of prestressing strand is required:
- Prestressed concrete bridges, parking structures, marine and chemically aggressive environments
- Post‑tensioning and some pre‑tensioning applications (use caution in fire‑rated pre‑tensioned elements)
Primary users:
- Structural and geotechnical engineers specifying prestressing materials
- Strand manufacturers and coating suppliers
- Quality control and testing laboratories
- Contractors, bridge and building owners, procurement teams
Related standards
Keywords: ISO 14655:1999, epoxy-coated strand, fusion-bonded epoxy, prestressing strand, coated and filled strand, holiday detection, pull-out test, prestressed concrete.