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Concrete Surface Preparation
The Navy considers concrete surface preparation and treatment to
be critical to ensure adequate bond between the substrate and the
external reinforcement. Included in the surface preparation is the
application of a primer that penetrates and seals the concrete.
Penetration of the primer is significant because it enhances the
tensile strength of the concrete while it prevents laminate deterioration
at the concrete interface due to moisture migration from the concrete.
NFESC pull-off tests showed the primer significantly increases the
tensile and impact strength of the first 1/8-inch (3 mm) layer of
concrete that is porous and microcracked (Reference 3).
Concrete surface preparation after repair generally took the course
directed by manufacturer’s recommendations. In case of a conflict
between the Navy’s specifications and manufacturer’s
literature and guidelines, the Navy’s specifications took
precedence. Surface preparation procedures required the application
of an epoxy penetrant/sealer/primer with a maximum viscosity of
100 centipoise.
The ideal concrete surface for applying external laminate reinforcing
is clean, dry, planar and abraded to roughness equivalent to a concrete
surface profile (CSP) 3 as defined by the International Concrete
Repair Institute (Reference 4). Form marks and surface discontinuities
were ground or knocked down with a small, compressed-air-driven
hammer or pneumatic grinder. The latter was also useful for feathering
voids and other small anomalies in the concrete surface. After removing
all the form marks and high points, the surface was abraded. Abrading
removes cement laitance from the surface and exposes the aggregate
for bonding with the epoxy matrix. The preferred method of abrading
the surface employed by the contractor is shot blasting wherein
all the shot is recovered with the removed material. Methods that
bruise the concrete (cause cracking in the concrete surface) were
not allowed.
Protruding tie wires, reinforcing chairs, paint, and rust stains
were removed. Surface indentations such as “bug holes”
that remained after grinding were filled and smoothed with shrink-resistant
polymer grout. Indentations in the bonding surface negate the laminate
bonding making it susceptible to peeling. Therefore, concave surface
areas were not allowed.
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