Structural aspects of repair - Concrete Repair - page 82

A3 - 2- 4. Comparison of Max. Carbonation with Min.Cover to
Reinforcement for Six Detailed Survey Locations

70

Max.CO2'
Rebar .

60

50

40

30

20

10

0

1 STN C, 2 STN B, 3 STN A, 4 PR G, 5 PR F, 6 STS F.
Spalls Spalls No Spalls Severe spalls Severe spalls No Spalls

Figure 3.7 Typical variation in carbonation depth and cover in one part of a structure.

the corrosion and in particular if calcium chloride is present beyond the
carbonation front.
When cutting out for a specific repair the rebar depth and the extent
of corrosion become clear. The carbonation depth can be easily checked
with phenolphthalein, but site checks for chlorides are more difficult. The
corrosion boundary on reinforcement is a guide to where current chloride
conditions are on the threshold for corrosion, but beware incipient anodes.
From this, an extrapolation for the next 20 years, with a margin for error,
can be made.
The profiling of the cut-out area for repair also needs to consider the
effectiveness with which the repair can be placed and its orientation with the
stress fields during repair and when dead load and live load are reapplied.

3.2.3 Incorporating additional reinforcement or replacing it

The essence of a structure is its ability to transfer shear, flexure and axial
compression from applied actions (dead and live load) to the ground and to
provide a sufficient degree of ductility and robustness. Some reinforcement
becomes redundant after construction or is oversized when appraised in
detail. Some structures are structurally inadequate because of errors in old