Constituent Materials and Properties - Strengthening Design of Reinforced Concrete with FRP - page 45

on polymer matrices, since they are widely used to strengthen concrete structures.
Resins or polymers are classified into thermosetting and thermoplastic matrices.

3.3.1 t hermoSetting r eSinS
Thermosetting resins are formed into a polymer matrix through an irreversible
cross-linking chemical process called resin curing . These resins are the most com-
monly used polymer system. This is due to the fact that they have low viscosity,
allowing thorough fiber immersion, and they require low processing temperatures
and short processing time. They also cost less than thermoplastic resins (Hyer 1998).
Resin shelf life refers to the amount of time that a resin system can be stored without
degradation prior to mixing (Barbero 2011). Resin pot life is the time span during
which mixed resin is still workable and applicable (Barbero 2011). The properties of
various widely used thermosetting resins are listed in Table 3.3 (Hyer 1998).

TABLE 3.3
Properties of Thermosetting Polymers at Room Temperature

Thermosetting Polymer

Property Polyester Vinyl Ester Epoxy Bismaleimide Polyimide

Density (kg/m 3 ) 1100-1500 1150 1100-

1400

1320 1430-1890

Tensile modulus
(GPa)

1.2-4.5 3-4 2-6 3.6 3.1-4.9

Shear modulus (GPa) 0.7-2 — 1.1-2.2 1.8 __

Tensile strength
(MPa)

40-90 65-90 35-130 48-78 70-120

Compressive strength
(MPa)

90-250 127 100-200 200 —

Elongation (%) 2-5 1-5 1-8.5 1-6.6 1.5-3

Coeff. of thermal
expansion
(×10 -6 /°C)

60-200 53 45-70 49 90

Thermal conductivity
(W/m/°C)

0.2 — 0.1-0.2 — —

Specific heat (J/kg/K) — — 1250-

1800

— —

Glass transition
temperature (°C)

50-110 100-150 50-250 250-300 280-320

Water absorption (%)
[24h @ 20°C]

0.1-0.3 — 0.1-0.4 — 0.3

Shrinkage on curing
(%)

4-12 1-6 1-5 — —

Source: Courtesy of Hyer (1998).