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Overview of Precured
Systems
Pre-cured FRP systems
consist of a wide variety of composite shapes manufactured in the system
supplier’s facility and shipped to the job site. Typically, an adhesive is
used to bond the precured flat sheets, rods or shapes to the concrete
surface or inserted into slots cut into the wall. The adhesive used to
bond the precured system to the concrete surface must be specified by the
system manufacturer. Adhesive selection is critical in that the adhesive
provides for the proper transfer of load between the surface of the
concrete and the cured reinforcement. Common types of pre-cured systems
are listed below:
Products
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Precured unidirectional
laminate sheets in the form of large flat plate stock or as thin ribbon
strips coiled on a roll.
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Precured multidirectional grids coiled on a roll or precut in sheet form.
Grids are able to be cut easily in the field using tin-snips.
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Precured shells in the form of shell segments cut so they can be opened
and fitted around columns or other elements. Multiple shell layers are
bonded to the concrete and to each other to provide seismic confinement or
strengthening.
Precured Grids
Grids are generally
produced with glass fiber or carbon fiber and are wet-out with a resin and
fully cured in the manufacturer’s factory. Grids are produced in a variety
of constructions from unidirectional to a balanced construction. Grid
reinforcements can be supplied with a wide range of tensile strength
properties. Tensile strengths in both the warp and weft direction can be
varied. Typically grid thickness ranges from 0.01”– 0.100” and
grid-opening sizes from 0.125 to 2 in. The product is typically supplied
in rolls although it may be cut to length and supplied in sheet form. The
product can be cut to size with a heavy-duty scissors or tin snips. The
grids are produced so the degree of cure and alignment is controlled. The
equipment used to produce these structural grids insures that warp and
weft continuous fibers are uniformly tensioned for consistent and uniform
fiber loading.
Installation/Application
Typically an adhesive is
used to bond the precured flat sheets, rods or shapes to the concrete
surface or inserted into slots cut into the substrate. The system
manufacturer must specify the adhesive used to bond the precured system to
the concrete surface. Adhesive selection is critical for the proper
transfer of load between the surface of the concrete and the precured
reinforcement. If an adhesive is not used, the system manufacturer will
provide details on the method for affixing their reinforcement system to
the surface of the concrete. Applying precured systems is similar to wet
lay-up system. The procedures are as follow:
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Prepare Substrate
– The
concrete, masonry or steel surface must be properly prepared prior to
bonding. There shall be no spalling or delamination in the case of
concrete and the corners must be ground to a minimum radius of 10mm (3/8
in.) or the recommendations of the precured system manufacturer. The
substrate surface is typically roughened by grinding or sandblasting.
Sandblasting is normally used on steel. Any unevenness in the concrete
or masonry is removed with a mineral-based re-profiling mortar.
Trowelable adhesives fill small holes or uneven surfaces before applying
FRP systems.
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Prime Concrete
Surface –
Some systems require the dust-free surface be coated with a primer.
Follow the system manufacturers recommended procedure. For steel, a
sandblasted surface yields the best results.
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Apply Epoxy –
The majority of systems require an adhesive be applied to the surface of
the concrete, masonry or steel prior to the FRP precured reinforcement
being pressed into the surface of the adhesive. If this is not the case,
follow the system manufacturer’s recommended procedures. The adhesive
thickness is critical to the performance of the system. Follow the
system manufacturers recommendation regarding the thickness of the
adhesive to be applied. The adhesive is applied to the surface using
a steel or plastic trowel or squeegee. Each adhesive has a working time
at a specific temperature. This information is available from the system
manufacturer.
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Place FRP Precured
material on the Structure –
After the adhesive
has been applied to the surface of the concrete, masonry or steel, the
precured FRP material should be placed in contact with the adhesive and
pressed into the surface of the adhesive following recommendations from
the system manufacturer.
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Cosmetic Topcoat–
A topcoat of epoxy can now be applied to the sheet to provide a cosmetic
finish. If applicable, quartz sand can be applied to the topcoat to
provide a textured surface for plaster or painting.
Note:
Installation/Application of procured grids follow the method described
above. The surface of the structure to be strengthened will have a
trowelable epoxy adhesive applied to the surface after the surface has
been prepared. The grids are then pressed into the surface of the epoxy
adhesive with the excess adhesive coming through the holes in the grids as
the grid is wrapped around the column or onto other surfaces to give the
correct number of layers to meet the design requirements. Following the
completion of the application of the grids, the excess epoxy adhesive on
the surface is smoothed to encapsulate the exterior of the grid structure
to create the finished structural grid system to create the strengthening
system.
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section: FRP Systems: Wet Lay-up
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Near Surface Mounted
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