Is excess cover good in insitu RC structures?

Many times, during my site inspections, I
have found fault with the Contractors for
providing an inadequate cover for the
reinforcements in R.C structures.
Obviously inadequate cover for the R.F
has to be rectified immediately as less
cover causes the larger crack widths in
concrete and thereby it exposes the
reinforcement to surrounding
environment to get corroded. This is an
important factor to consider in which
bridge structures as it withstand severe
environmental conditions.
Furthermore, an inadequate cover leads
to unsatisfactory fire resistant as well as
the under developed bond strengths
between concrete and R.F also. Hence
there should not be any argument
whether inadequate cover is acceptable
or not. The clear and loud answer is
NO!!!!!

Then what about the other side of the
story? In other words, is provision of an
extra cover than the specified limits
acceptable? Oki doki…take a little time
and come up with an answer………………..
Many distinguished concrete
specifications are very clear on this
matter. The tolerance for the concrete
cover is between +10 mm to -10 mm.
However some inexperienced contractors,
especially small scale subcontractors, do
posses a misconception that increased
concrete cover is acceptable and allowed
to go unnoticed. This is wrong…….
What is the underlying theory behind the
upper tolerance limit of the concrete
cover? The upper limit of the concrete
cover governs by its effect on Crack
widths. Generally the Crack width of the
concrete is governed by three factors
namely
1.) Tensile strain of the point
2.) Distance to the R.F bar from the
concerned point &
3.) Depth of the
tensile zone

In this case, the second factor is
significant and it governs the upper limit
of the concrete cover.  The increased
concrete cover leads to longer distances
of R.F bar from the cracking point.
Hence with an increased concrete cover,
the crack width also becomes larger.
So cover for concrete should be in its
specific limits whether it is plus or
minus…keep checking for that….
Oki guys…that’s it for today…Looking
forward to see your comments on this
topic…. Laters