Durability and Environmental Effects on Bond
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Aggressive Environment Exposure |
One of the compelling reasons for using Fiber Reinforced Polymer (FRP) materials
in highway structures is their chemical inertness to effects of de-icing salts and
marine environments. However, their vulnerability in other environments makes it
imperative to carefully evaluate the long-term performance before their adoption
in structural systems.
Corrosion of reinforcing and prestressing steel in concrete is a worldwide problem.
The passive layer that normally protects steel in concrete's alkaline environment
can be destroyed either by chloride contamination or by concrete interaction with
carbon dioxide from the air after an extended period.
In the case of bonded FRP, the materials are most often subject to the effects of
wind, rain, and sunlight, collectively referred as “weathering?or “aging? However,
it also may be subjected to alkali attack from the concrete pore solution. Both
of these are hostile environments that can degrade FRP material. The ability of
FRP to withstand the environments over its projected life is critical for acceptance
by design engineers.
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Ultravioilet (UV) Exposure |
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Water Exposure |
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Saltwater Exposure |
FRP composites have advantages that make them the materials of choice for many rehabilitation
and strengthening applications. However, life-cycle cost of FRP repairs must be
competitive in order for FRP composites to be used on a larger scale. Durability
is one of the most crucial elements governing life-cycle cost.
The MAS2000 Fiber Wrap System has been developed through extensive testing of long-term
durability of bond between the FRP materials and concrete. In these studies, the
bonded FRP elements were subjected to accelerated testing under severe environmental
exposures over a period of 17 months.
The choice of epoxy, method of installation and surface preparation are important
parameters considered in the study. Five different epoxy systems were tested. Test
specimens consisted of FRP sheets bonded to concrete slabs. A total of 24 unstressed
specimens were used in the study.
Five of these specimens were used as control cases and were not subjected to the
accelerated testing procedure. The 19 remaining specimens were exposed to four environments:
1) wet/dry cycles in salt water; 2) combined wet/dry and thermal cycles in salt
water; 3) outdoor UV exposure; and 4) air-conditioned laboratory exposure. The long-term
performance was evaluated qualitatively by comparison with the control case specimens.
Little deterioration was observed in the specimens exposed for 17 months. No deterioration
occurred in the control specimens. No discernible de-bonding or damage existed in
the specimens, although some discoloration occurred in specimens exposed to outdoor
UV conditions.
The data was used to modify and enhance the MAS2000 Fiber Wrap System. The modifications
resulted in a structurally efficient and durable system that is suitable for severe
environments.
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