Civil Engineering Reference
In-Depth Information
weight loss. However, a decrease in the flexural strength of the specimens
exposed to corrosive agents was registered and this effect was more pronounced
at lower filler concentrations (Gorninski et al., 2007; Reis, 2009).
in most of their applications, PCs are exposed to outdoor environment.
Polyester and epoxy-based PCs are to some extent sensitive to degradation
effects due to natural weathering, with epoxy-based mortars being in general
more weather resistant than polyester-based ones. one-year outdoor exposure
to corrosive maritime environment has a moderate harsh effect on mechanical
flexural strength of both types of PCs (Ribeiro et al., 2008).
16.6 Coatings
16.6.1 Components and properties
Materials to protect the surface, also called coatings, of cement concrete
can be classified into three groups: pore liner (makes the concrete water
repellent), pore blocker (reacts with certain soluble cement constituents and
forms insoluble products) and coatings (form continuous film on concrete
surface) (Medeiros and Helene, 2009). The main function of a coating is to
prohibit water and any soluble salts from penetrating the concrete, causing
corrosion, leaking and other problems. Coatings must be also very effective
in minimizing the rate of corrosion once it has been initiated by preventing
further access of moisture and oxygen to the steel surface.
The coatings used for protecting concrete structures can be: cement-based,
polymeric resins and silane/siloxane products. They vary in terms of method
of application, durability performance and price. Most surface treatments must
be applied to a clean, dry and sound substrate at moderate temperature and
humidity conditions in a well-ventilated space. A relatively smooth surface
is needed for liquid applied membranes (Fowler and Whitney, 2011). Since
these conditions do not always prevail, the difficulty and cost in achieving the
appropriate installation conditions may influence the choice of a system.
The base polymers of polymeric coatings include, but are not limited to,
acrylics, epoxies, polyesters, polyurethanes, styrene-butadienes, polyvinyl
acetates, chlorinated rubbers. Silanes and siloxanes are also frequently used.
Thin polymer concrete overlays (TPCos), with a thickness of 25 mm or less,
are widely used as coatings. Their advantages include the rapid development
of high strength and the ability to cure or harden under a wide range of
environmental conditions, very low permeability, low weight due to the small
thicknesses, wear and abrasion resistance and resistance to a wide range of
aggressive chemicals, excellent bond to concrete, especially in the case of
polyester-styrene and epoxy resins (Fowler, 1998; Tabor, 2004).
The bond between a coating material and concrete substrate must remain
intact: even with proper surface preparation, this bond can fail. For instance,
