5.2—Internal structural repair (restoration to
original member strength)
5.2.1 Description (repair of cracks)—For cases requiring
repair without increasing the member’s structural strength
capacity, epoxy injection is commonly used to restore the
member. Epoxy injected into the crack restores the concrete
section to its precrack condition. The epoxy tensile bond to
the concrete substrate is stronger than the concrete’s tensile
strength, and subsequent loads applied to the concrete section
consequently fail at the same load as that of the original
uncracked member section. Therefore, resin injection by itself
is not a strengthening method but is considered a restoration
method that restores the section to its original member
strength. Refer to ACI 503R and ICRI 03734.
Strengthening is provided by installing additional reinforcement
across the failure plane in combination with the
resin injection. Frequently, internal or external reinforcement is
installed in combination with the epoxy injection for
strengthening and restoration.
5.2.2 Advantages and typical use—Crack injection can be
successfully performed on cracks as narrow as 0.013 mm
(0.005 in.) in width with generally accepted epoxy injection
resins. Cracks with less width can be injected with epoxy or
other polymer systems having a low viscosity of 200 cps
(ACI 503R and 224.1R).
5.2.3 Disadvantages—Special considerations should be
made for bond strength for elevated temperatures. Epoxies
and other resins lose strength when exposed to fire or