FRP bar properties - Reinforced Concrete with FRP Bars: Mechanics and Design - page 36

the analyses showed that there is no degradation of the GFRP bars in the
real-life concrete structures. The analyses also indicated:
• No alkali ingress was observed in the GFRP bars from the concrete
pore solution.
• The matrix in all GFRP bars was intact and unaltered from its origi-
nal state.
• Neither hydrolysis nor significant changes in the glass transition tem-
perature of the matrix took place after exposure for 5 to 8 years to
the combined effects of the alkaline environment in the concrete and
the external natural environment.
Bond-to-concrete behavior. Bond between FRP and concrete depends on
the design, manufacturing process, mechanical properties of the bar itself,
and the environmental conditions [46-50]. Bond stresses at the FRP bar/
concrete interface are transferred by chemical bond (adhesion resistance of
the interface), friction, and mechanical interlock due to irregularity of the
interface. In the FRP bar, bond stresses are transferred through the resin
to the reinforcement fibers. The bond behavior of an FRP bar is, therefore,
limited by the shear strength of the resin [51-58].
3.2 TEST METHODS
Due to differences in the physical and mechanical behavior of FRP mate-
rials compared to steel, unique test methods for FRP bars are required.
Standards development organizations have developed consensus-based test
methods for FRP reinforcement for use in structural concrete.
The American Society for Testing and Materials (ASTM) International
and the International Organization for Standardization (ISO) offer stan-
dardized test methods related to the use of FRP composites in structural
engineering. Testing procedures directly have also been developed by the
American Concrete Institute (ACI). The document “Guide Test Methods for
Fiber-Reinforced Polymer (FRP) for Reinforcing or Strengthening Concrete
and Masonry Structures” [59], prepared by the ACI Committee 440, pro-
vides model test methods for the short-term and long-term mechanical,
thermomechanical, and durability testing of FRP bars not yet standardized
by ASTM. These recommended test methods are based on the knowledge
gained from research results and literature worldwide.
3.2.1 ASTM test methods
Table 3.2 provides a list of the test methods applicable to FRP bars for
use in nonprestressed concrete as available in ASTM. Of these methods,