Civil Engineering Reference
In-Depth Information
most common reason for concrete repair; however, there are many other
possible causes for concrete deterioration. The following sections list some
of the more common causes of concrete deterioration (see also
Chapter 1).
Chloride-induced reinforcement corrosion
In most cases the chlorides will be externally derived from sources such
as road de-icing salts but it is essential to explore the possibility that the
chlorides may have been originally incorporated in the concrete, as in some
older concrete structures where calcium chloride may have been used as an
accelerator. It is also important to bear in mind that carbonation may modify
the distribution of chlorides in the concrete and lead to apparently low levels
of chloride at the surface whilst chloride levels at greater depths may be
sufficiently high to cause corrosion. Petrography is useful in establishing the
pathways for chloride ingress and SEM/EDXA can be used to map out chloride
distribution around cracks, analyse corrosion products and investigate the
relationship between chlorides and carbonation. The corrosion products
resulting from chloride-induced corrosion can be very fluid and substantial
loss of reinforcement cross-sectional area can result from corrosion with
little or no associated concrete expansion.
Figure 2.4
shows the leakage of
fluid reinforcement corrosion products along microcracks in the vicinity of
corroded reinforcement affected by chloride ingress.
repair mortar and a mechanically roughened concrete surface. The repair mortar
has separated from the concrete surface and a crack between the repair material and
concrete surface occupies the central part of the field of view. The crack surface is
coated with reinforcement corrosion products and some of the cracks within the
surface of the concrete substrate also contain corrosion products indicating on-going
corrosion since the repair of the concrete surface. Note the shattering in the flint
coarse aggregate particle visible on the left side of the field of view. There is also
some patchy carbonation of the cement paste either side of the crack along the repair/
substrate interface.
