Civil Engineering Reference
In-Depth Information
Although the guarantee of a successful repair will still not be achieved, if
a system has been properly designed, specified and applied it has the best
chance of achieving the required end result (Atkins, 2007).
17.3 The specification of surface coatings/treatments
The use of protective surface barriers can be related to the age and condition
of the concrete, as discussed below.
(i) New concrete, satisfactory quality: 'normal specification' of
surface treatment
Surface barriers would normally be specified at the design stage where there
is an obvious incompatibility between the performance of concrete and a
particular service environment or demand. Hence, the predominant reasons
for use are likely to be the prevention of direct deterioration and the control
of ingress/contact.
In exceptionally aggressive environments, they may be used to enhance
the resistance to indirect deterioration due to reinforcement corrosion.
However, as surface treatments inevitably require maintenance, other
options may be preferable (e.g., improved concrete mix design, increased
cover, alternative forms of reinforcement).
Coatings may also be specified initially where both chlorides and sulphates
are present (even for the lower classes of sulphate exposure) as sulphate-
resisting Portland cement has a relatively low resistance to chloride ingress,
due to its reduced tricalcium aluminate content. However, blended cements,
such as Portland-Pfa or Portland-Blastfurnace cements, are usually specified
to achieve the required durability in these conditions.
(ii) New concrete, unsatisfactory quality: 'remedial specification'
of a surface treatment
Here, surface barriers may be used to alleviate potential deterioration due to
reinforcement corrosion arising from an inadequate mix design, insufficient
cover or the poor compaction/cure of concrete. It is well established that
proprietary products can provide effective chloride and carbonation barriers
over lengthy periods of service (although they are not a substitute for correct
initial specification and placement of the concrete).
(iii) Concrete undergoing deterioration: 'repair specification' of a
surface treatment
Where direct deterioration due to chemical/physical effects has occurred,
reinstatement by the simple application of a surface treatment may be
feasible at an early stage, particularly if a thick lining or render is used. It
