Material properties - Reinforced Concrete with FRP Bars: Mechanics and Design - page 22

2.3.1 Fibers
Fibers commonly used are glass, carbon, aramid, and basalt. Glass fibers
offer an economical balance between cost and specific strength proper-
ties; this makes them preferable to carbon and aramid in most reinforced
concrete (RC) applications. Basalt fibers have recently emerged as an alter-
native to glass fibers. Typical properties of glass, carbon, aramid, and basalt
fibers are listed in Table 2.1.
2.3.1.1 Glass fiber
Glass fiber is primarily made from silica sand and is commercially avail-
able in different grades. The most common types of glass are electri-
cal (E-glass), high-strength (S-glass), and alkali-resistance (AR-glass).
E-glass presents high electrical insulating properties, low susceptibility
to moisture, and high mechanical properties. S-glass has higher ten-
sile strength and modulus, but its higher cost makes it less preferable
than E-glass. AR-glass is highly resistant to alkali attack in cement-
based matrices, but, at the moment, sizings compatible with thermoset
resins that are commonly used to pultrude FRP bars are not available.
Composites made from glass fiber exhibit good electrical and thermal
insulation properties.
2.3.1.2 Carbon fiber
Carbon fiber is made from polyacrylonitrile (PAN), pitch, or rayon fiber
precursors. PAN-based carbon fiber is the predominant form used in
civil engineering applications. PAN-based carbon fiber presents high
strength and relatively high modulus. Pitch-based carbon fiber has higher
modulus but lower strength, which makes it suitable for aerospace appli-
cations. Rayon and isotropic pitch precursors are used to produce low-
modulus carbon fiber. Based on its mechanical properties, carbon fiber
can be classified as high modulus and low modulus. Carbon fiber has
high fatigue strength, high resistance to alkali or acid attack, a low coef-
ficient of thermal expansion (CTE), relatively low impact resistance,
and high electrical conductivity; it can cause galvanic corrosion when in
direct contact with metals. Moreover, it is not easily wet by resins; there-
fore, sizing is necessary before embedding it in the resin. Generally, car-
bon fiber is about 10 times more expansive than glass fiber and exhibits
strength and modulus about three times higher than glass.
2.3.1.3 Aramid fiber
Aramid fiber is an aromatic polyamide organic fiber. It offers good
mechanical properties at a low density, high toughness, and high impact