Adhesive Selection
The strengthening of existing structures using Fiber Reinforced Polymer (FRP) is
similar to that of using bonded steel plates. FRP plates are adhesive bonded to
the tension flange of a structural member, thereby increasing both stiffness and
strength. Advantages of this system include the ease of application and elimination
of special anchorage devices. Work can be performed while the structure is in use,
and vertical clearance is not reduced. Moreover, the potential problem of corrosion
associated with steel plates is eliminated.
A most important parameter in a composite repair is the bond between the concrete
and the carbon materials. Major advantages of adhesive bonding are:
- The applied load is distributed over a much larger area compared to other methods
of fastening, thus reducing the unit stress on the elements that are bonded;
- The shape of the elements need not be altered when adhesive is used;
- The adhesive bonding line also serves as a moisture barrier;
Adhesives can be broadly divided into two categories: solvent-free adhesives that
cure by polymerization of monomeric resins and; water-borne adhesives that also
cure by polymerization but under damp surface conditions. Epoxy adhesives are the
most commonly used because of their excellent adhesion and molecular properties.
The selection of an adhesive for a specific application depends on the following
factors:
- The type and magnitude of stresses;
- The surface conditions during application;
- The desired strength levels of the adhesive;
- The temperature and humidity levels;
The adhesive selected should be capable of transferring loads to the same degree
as the structural elements that are bonded together. The selection procedure should
also take into account the possibilities of surface contamination, temperature of
the contact surfaces, and dampness of the substrates.
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| Bond Failure Through Substrate |
Tensile Rupture of FRP REinforcement |
End Peeling of Rigid Plates |
The bond strength of an adhesive depends on its adhesion and the cohesive strength
of both the substrates and the adhesive. The most important property influencing
the selection of an adhesive is its inter-laminate shear strength. The selection
of an adhesive most suited to the application must take into consideration the detrimental
effects of temperature, moisture, fire and chemical exposure.
Adhesives typically are applied using a brush or roller, although techniques such
as spraying and trowel application can be used. An important consideration in the
application of an adhesive is that the concrete surface should be completely covered,
or “wetted? by the adhesive.
Through extensive testing under a variety of exposure conditions, SDR has developed
several types of adhesives suitable for a wide variety of environments. The MAS2000
Fiber Wrap System is designed to suit the type of application and ensure optimum
performance and long-term durability.
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