Installation - Strengthening Design of Reinforced Concrete with FRP - page 219

Concrete Substrate

Shear Crack

Shear Stresses

FRP Laminate

Normal Stresses

FIGURE 8.1 Intermediate crack-induced FRP debonding.

in a study by Saadatmanesh and Ehsani (1990), which showed that the
effectiveness of FRP plates in strengthening beams is highly dependent
on the selection of the resin adhesive.

2. Crack injection by resin

Cracks wider than 0.3 mm (0.01 in.) may negatively impact the
behavior of FRP-strengthened members by provoking early pre-
mature delaminations or fiber kinking (ACI 440.2R-08), as seen in
Figure 8.1. Such cracks need to be epoxy-injected prior to surface
preparation according to ACI 224.1R-07. For more detailed step-by-
step procedure, refer to Reed et al. (2003, 2005). Narrower cracks in
more aggressive environments need to be sealed to prevent corrosion
of the main steel reinforcement.

3. Damage caused by corrosion

When it is evident that the member to be strengthened has undergone
corrosion damage, the cover needs to be removed and the corroded bars
need to be cleaned. The cover must then be repaired prior to applying
FRP materials to avoid putting the integrity of the system in question,
as seen in Figure 8.2.

4. Surface preparation

Whenever the bond between the substrate and FRP system is critical for
the load transfer, special attention must be provided to surface prepara-
tion in the so-called bond-critical applications like the flexural or shear
strengthening of beams, columns, slabs, or walls. This surface prepara-
tion is not so critical for the so-called contact-critical applications that
have adhesive bonding during installation. A typical application of this
category is lateral confinement of columns.

• Surface preparation for bond-critical application

The surface to which the FRP is to be bonded should be free of weak or
loose material and should be recently exposed to the aggregate level by
means of grinding or sandblasting (Rasheed et al. 2011; Larson, Peterman,
and Rasheed 2005). Grinding typically uses a diamond rotary grinder to
grind the surface until it is roughened to the aggregate level, as seen in
Figure 8.3.