Mechanical and Durability Screening Test Methods for Cylindrical CFRP Prestressing Tendons

Abstract

Concrete prestressed with carbon fiber–reinforced polymer (CFRP) tendons beneficially utilizes the strain capacity and durability characteristics of the CFRP material. However, changes to CFRP tendon material formulations or production processes present a challenge when building up a body of knowledge to inform the long-term behavior of a prestressed concrete system. Initial qualification tests can help identify the potential for fiber–reinforced polymer (FRP) tendons to meet long-term mechanical and durability requirements. Protocols that can be undertaken on commercially produced cylindrical FRP pultrusions are particularly advantageous because the constituent materials and manufacturing processes are representative of the actual product. Selected mechanical and durability characterization approaches, and their suitability for adaptation for wet specimens with cylindrical geometries, were critically assessed. A series of qualification tests were then conducted on CFRP tendons with three different resin systems. Tendon samples were exposed to wet environments to evaluate the longer-term solution uptake and associated mechanical durability implications. While characterization measures such as the glass transition temperature, optical imaging, and moisture uptake provided comparative results, the correlation with mechanical properties obtained from uniaxial tension, double notch shear, and torsion tests was unclear. Using a subset of the mechanical test protocols, a retrospective analysis of CFRP tendons extracted from a prestressed concrete lighting pole under sustained load for 16.5 years was also reported.