Civil Engineering Reference
In-Depth Information
reduce the corrosion current compared with the untreated specimens, bringing
about a reduction of corrosion by-product (Pfeifer, 1987). good performance
has also been reported for silane-siloxane treatments: these sealants with a
topcoat and an acrylic coating were among the most effective in reducing
reinforcement corrosion.
Vassie (1991) reported that the most effective coatings to slow down the
corrosion rate of active steel in concrete (0.5 W/C ratio) were: solvent-free
urethane, alkyl alkoxy silane, silane/acrylic and liquid plastic dressing. The
alkyl alkoxy silane, in particular, was able to reduce the ongoing corrosion
by around 35%; however, it failed to stop the corrosion completely.
Medeiros and Helene (2009) compared different surface treatments (silane/
siloxane dispersed in solvent, acrylic coating, polyurethane coating) able to
inhibit chloride penetration in concrete. They concluded that the polyurethane
coating presented the best efficiency in reducing the chloride penetration (up
to about 85%). The authors, however, pointed out that their result cannot be
universally considered since the efficiency of the treatment does not depend
only on the type of resin that composes it.
Different authors reported the success of methylmethacrylate impregnation
on US bridges to prevent the onset of corrosion (Smoak, 1990; Weyers et
al., 1990). A silane coating was also found to be effective in wet zones
of a bridge (Van es, 1992), even though the effectiveness of silane in a
freeze-thaw environment is somehow questionable: silane does not improve
the freeze-thaw resistance of concrete (Perenchio, 1988). However, other
researchers reported that the freeze-thaw resistance of concrete treated with
silanes and siloxanes, with or without an upper coat of acrylic, was much
better than that of untreated concrete (Basheer et al., 1990; Mcgill and
Humpage, 1990). This discrepancy can be explained taking onto account two
different effects: if the concrete is initially dry, the application of silane will
ensure a low degree of water saturation during freezing and thawing. As a
result, the resistance offered by the surface-treated concrete to freeze-thaw
deterioration may be significant. On the other hand, if the concrete is saturated,
the application of silane may not improve the resistance to freeze-thaw
deterioration because dilatation of water-filled capillary pores will take place
as a result of expansion of the water already contained in concrete during
freezing.
16.6.2 Durability
The durability of surface treatments depends on the type of polymer on which
the coating is based and, very importantly, on the depth of penetration. A
significant depth of penetration has been generally observed for silane and
siloxanes (Basheer et al., 1997). other polymeric treatments penetrate to a
few millimeters or less and, in fact, many form a film on the surface.
