Civil Engineering Reference
In-Depth Information
is more likely, however, that significant preparation will be required before
coating (i.e. cutting back, cleaning and profile restoration).
For structures that have been in service for a significant period, a
distinction must be made between the potential effectiveness of surface
treatments applied before/after the initiation of reinforcement corrosion;
also between chloride ingress and carbonation.
Prior to initiation
Appropriate surface treatments can effectively inhibit the progress of
carbonation, reducing its rate to a negligible level. Hence, the service life of
a structure can be extended considerably where carbonated concrete in the
cover zone has not reached the reinforcement.
The value of surface treatments is more debatable when chloride ingress
has occurred. The rate of chloride migration to the reinforcement may be
reduced by preventing additional penetration and by limiting the internal
moisture state of the concrete. However, it is unlikely that corrosion will be
prevented in the longer term - or even the short/medium term if chloride
ingress is at a high level prior to coating.
After initiation (following carbonation or chloride ingress)
In this case, surface barriers can only be effective by limiting the ingress of
oxygen and/or moisture. As only very small amounts of oxygen are required
to fuel the corrosion process, even the most (oxygen) impermeable surface
treatment is unlikely to be effective. However, attempting to maintain the
concrete in either a very dry or a water-saturated condition may assist in
reducing the corrosion rate.
After initiation, therefore, surface treatments are likely to be cost-effective
only where a relatively short extension of service life is required, or when
used in conjunction with other methods such as sacrificial anode cathodic
protection to reduce the work required from such systems and extend their
life.
Prior to carrying out any repair, it is essential that a proper assessment is
made of the defects in the concrete and their causes, and of the ability of the
structure to perform its function.
17.3.1 Additional comments
Although a detailed discussion of the applications summarised in
Tables 17.1
and
17.2
cannot be given here, concise information, in most cases, can be
obtained readily from the publications listed in the Bibliography. Some brief
comments regarding several particular uses are given below, however, as
published information in these areas is more scattered. These examples also
serve to illustrate the more general point that specialist knowledge is often
essential, even when considering seemingly simple applications.
