Civil Engineering Reference
In-Depth Information
if the coating is highly impermeable to water vapor, water may condense at
the concrete/coating interface and destroy the bond. generally speaking, the
adhesion strength of a resin-based coating to concrete is somehow higher
that that measured for cement-based coatings (Al-Dulaijan et al., 2000a). The
epoxy-based coatings display a better adhesion to concrete substrate than the
acrylic-based ones (Al-Dulaijan et al., 2000b). in addition, the conditions
at which the cure of the resin takes place have a noticeable influence on
the adhesion exerted to concrete: the adhesion decreases when the substrate
is wet and is promoted by moderate (at least 23 °C) curing temperatures
(Littmann and Schwamborn, 1999).
Surface treatments should be as permeable to water vapor as the untreated
concrete, in order to ensure that concrete, especially in freezing climates,
has sufficient permeability to allow the substrate (and any reinforcement
it contains) to remain substantially dry. it is reported that silicon-based
treatments, in particular silanes and siloxanes, possess these characteristic
(Basheer et al., 1997). epoxy resins, especially if applied in multiple coats,
and acrylic coatings decrease to some extent the breathability of concrete. in
the case of acrylic coatings, however, in the longer term there is no difference
in permeability between untreated and surface-treated concretes (Basheer et
al., 1990).
A high resistance to liquid water penetration must be first assured by coatings:
epoxies, silane-based coatings, methylmethacrylate, alkyl alkoxysilane and
oligomeric siloxane have been found to be very effective in reducing the
water intake of concrete. Silane-siloxane was found to be slightly inferior
to pure silane in reducing the sorptivity of concrete. When an acrylic top
coat was applied on to the base coating of silane, superior performance is
obtained (Basheer et al., 1997). However, the protective properties of a
coating may degrade in the long term when the permeability of the coating
is increased by deterioration.
The surface treatments should also improve the resistance of concrete to
carbonation, chloride ingress, sulfate ingress, freeze-thaw, salt scaling and,
above all, corrosion of embedded steel (Basheer et al., 1997). referring to the
performance of the different coatings against carbon dioxide penetration, epoxy
resins and some acrylic coatings have been found effective as anticarbonation
coatings. Alky-alkoxy silanes do not improve the resistance of concrete to
carbonation, while siloxane with large alkyl group may marginally reduce
the carbon dioxide diffusion.
Although many polymeric coatings, such as those based on epoxies,
methylmethacrylates and polyurethanes, provide an excellent barrier against
the ingress of chloride ions into concrete (Pfeiffer and Scali, 1981), with a
consequent appreciable increase of the time to initiation of corrosion of steel
bars (Cleland and Basheer, 1995), the best performance is usually obtained
with silanes. it is reported that the application of a silane coating is able to
