Civil Engineering Reference
In-Depth Information
be optional, giving increased assurance of satisfactory durability. However,
coatings should not be viewed as a basis for reducing cover or for inadequate
mix design, placement and curing (although they are sometimes used as a
remedial measure following these actions). The need for enhancement/
change of appearance and/or the modification of other surface properties
may also vary from being essential to optional.
Wherever surface coating/treatment is optional, increased initial costs,
and the inevitable maintenance costs, must be balanced against the projected
in-service benefits.
A summary of the common reasons for applying coatings/surface
treatments to concrete is given in
Table 17.1.
Although these applications are
well proven, specific local conditions can affect performance significantly.
Consequently, particular requirements should always be discussed with
suppliers.
More specifically in relation to the protection and repair of concrete
structures, general principles for the use of products and systems - including
coatings and related treatments - are set out in the European Standard BS
EN1504-9: 2008 (BSI, 2008).
These principles, and the related methods that are relevant here, are
summarised in
Table 17.2.
As shown, there are eleven principles, six of
which are concerned primarily with defects caused by mechanical, chemical
or physical actions on the concrete itself, and five of which are specifically
concerned with reinforcement corrosion. A related European Standard BS
EN1504-2:2004 (BSI, 2004) deals in detail with the performance properties
of these products and systems.
When applying surface protection to concrete, BS EN 1504-2:2004
suggests that products can be assigned to three main categories:
•
Hydrophobic impregnation (H) - these materials penetrate the concrete
and leave a water-repellent, molecular lining on the surface of the pores.
They encourage the concrete surface to shed water but do not prevent
water ingress under significant pressure as the pores essentially remain
open.
•
Impregnation (I) - these materials impregnate the concrete and block
the pores.
•
Coatings (C) - coating systems are those that adhere to the outer surface
of the concrete.
These in turn relate to the repair principles in BS EN 1504 Part 9:
•
Principle 1: Protection against ingress (PT)
•
Principle 2: Moisture control (MC)
•
Principle 5: Physical resistance/surface improvement (PR)
•
Principle 6: Resistance to chemicals (RC)
•
Principle 8: Increasing resistivity by limiting moisture content (IR).
