Civil Engineering Reference
In-Depth Information
and remove the surface layer of 2
3 mm thickness to reach the bare surface. Finally, blow
away dust particles using compressed air without grease. If concrete surface is not dirty
and worn the bonding area could be polished directly and the surface layer of 1
∼
2mm
thickness removed. After flushing away dust particles with compressed air or clear water,
use absorbent cotton with acetone to wipe the surface.
b. The bonding area of new concrete should be brushed with a wire brush, then brushed
with a scrubbing brush dipped in ecient detergent or flushed with pressurized water. Ad-
hesive is smeared till concrete has dried completely.
c. Concrete members that are less than 3 months old or in high humidity should be dried
artificially.
(2) Treatment of steel surface before sticking
a. Removing rust and coarsening should be done. Steel plates with little or no rust could
be polished with grit blast, coated abrasive or grinding wheel till appearance of metallic
luster. Coarser is better. The polished grain should be perpendicular to the direction of
forces applied to the steel plate. After polishing, wipe with absorbent cotton dipped in
acetone. After submersion in hydrochloric acid for 20 minutes to remove rust, steel plates
that rusted deeply should be flushed with limewater to counteract the acid ions, and then
polished using grinding wheel.
b. If possible, the retrofitted member should be unloaded before sticking. In the case of
jack unloading, multi-point lifting should be used for the beam bearing uniform loads for a
main girder with a secondary beam, a jack of appropriate size based on standards (and will
not produce cracks) should be installed below each secondary beam.
(3) Adhesive preparation
Structural adhesive JGN composed of two components should be prepared according to
instructions for product use and tested. Remove all grease, dirt, and rainwater from the
adhesive container and mix the adhesive in one direction only.
(4) Sticking steel plates
a. Adhesive should be smeared on the processed concrete and steel surface using a spatula
toathicknessof1
∼
3 mm, thick in the center and thin at the edge. The steel plate should
be attached at a preset position. For attachment at elevation, one layer of dewaxing glass
fiber fabric may be added to prevent flowing. If no hollow sound occurs when the surface is
knocked with a hammer, the steel plates are attached to the concrete; otherwise they should
be removed and attached again.
b. Attached plates should be clamped or fixed with strutting at proper pressure and
excess cement extruded from the edges of steel plates should be removed.
(5) After sticking
a. Structural adhesive cures at normal temperature. If temperature is maintained at 20
◦
C
or higher, clamping or strutting can be removed after 24 hours and the retrofitted member
can bear force after 3 days. If temperature is below 15
◦
C, artificial heat should be applied
with an infrared lamp.
b. Mortar should be stuccoed on the plate surface. For plates with large surface areas,
installing a layer of steel wire or pea stones will aid bonding.
(6) Quality inspection
a. Bond compaction can be checked by ultrasonic waves or lightly knocking with a hammer
after removing clamps or strutting. Bonded steel plates are ineffective and should be removed
and restuck if the bonding area in the anchorage area is less than 90% (70% for nonanchorage
areas).
b. For major projects, a sample should be taken for load testing to confirm the effectiveness
of the retrofit. The design should meet the requirements for structural deformation and
cracking under normal load.
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