Constituent Materials and Properties - Strengthening Design of Reinforced Concrete with FRP - page 56

TABLE 3.5
Environmental Reduction Factors for Different Exposure Cases and FRP
Systems

Environmental
Reduction Factor, C E

Exposure Conditions Fiber Type

Interior exposure Carbon 0.95

Glass 0.75

Aramid 0.85

Exterior exposure (bridges, piers, and unenclosed
parking garages)

Carbon 0.85

Glass 0.65

Aramid 0.75

Aggressive environment (chemical plants and
wastewater treatment plants)

Carbon 0.85

Glass 0.50

Aramid 0.70

Source: Courtesy of ACI 440.2R-08.

and thickness of the cured composite system. This is due to the fact that the wet lay-
up process has controlled fiber content and variable resin content that depends on the
installer (ACI 440.2R-08). It is very important to note that net fiber area properties
are not the same as dry fiber properties, but rather the same as the laminate or com-
posite properties with known fiber content. Since the thickness of the FRP sheet is
very small, the corresponding strength and modulus values are high because ( f fu A f )
or ( E f A f ) are constant for a composite.
For practical and design purposes, FRP mechanical properties are needed.
ACI 440R-07 reports typical values for sheets and plates from various manufacturers for
materials used in civil infrastructure-strengthening applications, as shown in Table 3.6.
It can be seen from the values in Table 3.6 that CFRP typically has higher modulus and
tensile strength and lower ultimate strain than GFRP, as shown in Figure 3.10.
On the other hand, the Delaware Encyclopedia of Composites (Zweben 1989)
reports typical composite mechanical properties used in aerospace applications.
These values are listed here for comparison purposes. It is evident that the lami-
nate properties of the materials used for aerospace applications clearly exceed those
of plates used for civil engineering applications due to the higher control over the
manufacturing process involved (heating, pressure, and vacuum). On the other hand,
the FRP sheet properties (Table 3.6) may be seen to exceed those of aerospace com-
posites (Tables 3.7-3.12), which is due to the fact that sheet properties are based on
net fiber area and not on composite laminate area. For example, MBrace EG 900
glass sheet has a net fiber modulus of 72.4 GPa, and multiplying this by the fiber vol-
ume fraction of 0.6 yields 43.44 GPa for the composite, which is close to the 45 GPa
reported in Table 3.7 for E-glass. Similarly, the tensile strength has a net fiber value
of 1517 MPa, and multiplying this by 0.6 yields 910 MPa for the composite, which is
slightly less than the 1020 MPa reported in Table 3.7. Further properties of unidirec-
tional, cross-ply and angle-ply laminates are given in Table 3.13 (ACI 440.2R-08).