Material properties - Reinforced Concrete with FRP Bars: Mechanics and Design - page 26

a wide variety of fibers. Epoxies have high corrosion resistance and are
less affected by water and heat than other polymeric matrices. Their
disadvantages are a high cost and long curing period (a postcuring process
is generally required). Epoxy resin can also be formulated with different
materials or blended with other resins to achieve specific performance
features. Epoxies are primarily used for fabricating high-performance
composites with superior mechanical properties, resistance to corro-
sive liquids and environments, superior electrical properties, and good
performance at elevated temperatures. Epoxy resins are compatible with
glass, carbon, aramid, and basalt fibers. However, their use in the pultru-
sion industry is limited.
2.3.2.2 Polyesters
The main advantage of polyester resins is a balance of good mechanical,
chemical, and electrical properties; dimensional stability; cost; and ease of
processing. Polyester resins are, generally, relatively inexpensive and offer
good mechanical and electrical performance. Because polyesters can be
chemically tailored to meet the requirements of a wide range of applications,
a number of specialty polyesters, which address specific performance such
as flexibility, electrical insulation, corrosion resistance, heat and UV light
resistance, fire retardancy, and optical translucence, are available. Styrene
is usually mixed in large quantities (more than 10% by mass of the poly-
mer resin) to give a low viscosity liquid. Their use in the manufacturing of
FRP bars is discouraged because of lower chemical resistance as compared
to vinyl esters.
2.3.2.3 Vinyl esters
Vinyl esters exhibit some of the beneficial characteristics of epoxies such
as chemical resistance and high strength as well as those properties of
polyester such as viscosity and fast curing. Vinyl esters exhibit good alkali
resistance and have good wet-out and good adhesion with glass fiber,
which makes them the preferred choice to manufacture GFRP (glass FRP)
composites.
2.4 MANUFACTURING BY PULTRUSION
The FRP bar is typically manufactured by pultrusion or variations of this
process. Pultrusion is a continuous molding process that combines fiber
reinforcement and thermosetting resin. This process is ideal for the con-
tinuous fabrication of composite parts that have a constant cross-sectional
profile such as bars.