S. Harichandran, Ph.D., P.E., F.ASCE
Department of Transportation
2004 - September 2007
structures that are damaged due to cracking and spalling
associated with corrosion of reinforcing bars are
often repaired using shallow depth surface patches.
Cracking and full or partial delamination of the patch
repairs due to shrinkage and continued corrosion is
generally unavoidable. The repairs typically last
only for a few years in corrosive environments associated
with coastal regions or where deicing salts are used.
The objective of the research was to develop an improved
repair method for shallow depth surface patches.
use of a fiber reinforced polymer (FRP) fabric applied
as an overlay on top of a traditional polymer concrete
patching material was investigated as a means of improving
the durability of shallow depth patches. The FRP overlay
can serve as a secondary reinforcement and act as
a barrier against the diffusion of moisture and chloride
ions, thereby improving the performance of the patch
by reducing cracking and slowing down the corrosion
process. Two-dimensional finite element analysis was
used to select a suitable FRP material and configuration
for the overlay. The effectiveness of the proposed
improved repair method was assessed using accelerated
corrosion testing of rectangular concrete prism specimens
with a polymer concrete patch and an FRP overlay.
Reinforcement mass loss and expansive strains in concrete
due to corrosion were measured on specimens with and
without the FRP overlay. The measurements indicated
reductions in concrete strains, crack propagation
and corrosion level when the FRP overlay was used.
Three-dimensional finite element analysis was conducted
to understand the influence of using an FRP overlay
on the concrete stress distribution and the arrest
element (FE) simulations indicated that a single layer
of bi-directional glass FRP fabric was sufficient
to withstand the load due to corrosion-induced swelling.
Accelerated corrosion tests (see Fig. 1) indicated
that the FRP overlay delays the onset of cracking
and changes the crack pattern. When an overlay is
not used, corrosion induced swelling causes a main
crack to initiate in the patch and propagate downward
toward the bottom of the beam. When an FRP overlay
is used, the main crack initiates in the concrete
and propagates sideways away from the region influenced
by the overlay. The FE analysis predicted the crack
patterns observed in the experiments reasonably well
(see Fig. 2). It indicated that, based on mechanical
effects alone, the initiation of cracking is delayed
in the presence of an overlay until more of the rebar
corrodes. The change in the crack pattern can delay
the migration of moisture, oxygen and chloride to
the corroding bar since the crack does not open through
the concrete cover. This effect together with the
delay of cracking should increase the durability of
the patch repair. The accelerated corrosion test confirmed
that the corrosion rate was reduced when an FRP overlay
was used, most probably due to the reduction in the
diffusion of chloride ions, moisture and air through
the concrete and patch. The mechanical enhancement
provided by an FRP overlay, together with reduction
in diffusion of moisture and chloride ions that it
may cause, therefore provides considerable improvement
in the durability of patched concrete beams against
corrosion (Harichandran and Nossoni 2008).
1 Crack patterns due to corrosion: (a) Pattern
1, and (b) Pattern 2
TCI along different crack paths: (a) Crack Pattern
1, and (b) Crack Pattern 2
enhanced durability resulting from the use of an FRP
overlay on top of a traditional polymer concrete patch
will reduced the maintenance cost and labor associating
with repatching bridges.
R. S., and Nossoni, G. (2008). "Improved shallow
depth patches for concrete structures." Report
No. RC-1502, Michigan Department of Transportation,
G. and Harichandran, R. S. (In press). "Improved
repair of concrete structures using polymer concrete
patch and FRP overlay." Journal of Materials
in Civil Engineering, ASCE.
G., and Harichandran, R. S. (2007). "Evaluation
of shallow depth patches in concrete bridges reinforced
with FRP overlays." Proceedings, 8th International
Symposium on Fiber Reinforced Polymer Reinforcement
for Concrete Structures, Patras, Greece.
G., and Harichandran, R. S. (2007). "Improved durability
of patched concrete bridges against corrosion by
using an FRP overlay." Proceedings (CD-ROM), 84th
Annual Meeting of the Transportation Research Board,
Washington, D.C., Paper No. 07-2594.