Civil Engineering Reference
In-Depth Information
epoxy-based coatings. Moreover, the two polymer-based coatings showed
better performance than a cement-based coating in terms of water absorption,
water permeability, chloride permeability and adhesion.
good durability to biogenic sulfuric acid has been reported by De Muynck
et al. (2009) for epoxy and polyurea coatings for sewer pipes. epoxy coatings
were found particularly effective in protecting concrete from microbiological
attack taking place in cooling towers, typically caused by sulfur oxidizing
or other acid-producing bacteria (Berndt, 2011).
16.7 Adhesives
16.7.1 Components and properties
The cement concrete deterioration manifests itself in the form of spalling and
cracking of concrete, caused by reinforcement corrosion and softening and/or
cracking. The formation of cracks and micro-cracks can be the consequence
of several phenomena, such as bleeding, shrinkage, dynamic loads, thermal
gradients, freeze-thaw and alkali-aggregate reaction. These unsealed cracks
and micro-cracks may form potential flow channels, providing easy access to
aggressive agents, independently of the porosity of the cement matrix. The
cracks have, therefore, to be repaired to achieve a reduction in permeability
and corresponding increase in durability.
The most frequently used method of repair is by conventional concrete
placement, consisting of the replacement of defective concrete with new
concrete. This technique is applicable to a wide range of situations and it is
usually also the most economical. However, it should not be used in situations
where an aggressive factor has caused the deterioration of the concrete
being replaced. For example, if the deterioration noted has been caused by
acid attack or abrasion-erosion, it may be expected that a repair made with
conventional concrete will deteriorate again for the same reasons.
Among other traditional techniques, especially for local interventions,
those involving the injections of mortar or reinforced grouted perforations
are employed to repair damaged concrete or upgrading structures under both
gravity and seismic loads. This traditional technique, however, presents
severe drawbacks, such as the scarce adhesion between two solids, the new
mortar and the old concrete (Burlamacchi, 1994). Other disadvantage are
related to esthetics and functionality because of the possible obstruction of
new areas, long time of interventions and therefore of activities interruption,
conservation when referring to historical buildings and monuments.
Polymeric adhesives are frequently employed in substitution of cement
grouts. Thermosetting resins are generally used, being able to harden without
adversely affecting any metals or the concrete boundaries of the opening or
void into which it has been injected. They may contain various inert fillers
