Civil Engineering Reference
In-Depth Information
Uniform corrosion is more predictable and often easier to model and miti-
gate. Although carbonation-induced corrosion has been identifi ed in many
structures, chloride-induced corrosion is generally more prevalent (ACI
201.2R-08).
19.2.2 ASR
Another common mechanism of deterioration in concrete structures is
ASR. A comprehensive assessment of the mechanisms of ASR is beyond
the scope of this chapter and additional information on the mechanisms
and damage can be found in Glasser and Kataoke (1981) and Folliard
et al.
(2006). ASR was fi rst reported by Stanton (1940) and like corrosion, gener-
ates a product of larger volume that causes tension in the concrete. ASR
requires three conditions to occur: available alkalis in the pore solution,
reactive silica in the aggregate, and suffi cient moisture in the concrete.
When these conditions are present, a chemical reaction between the reac-
tive silica in the aggregate and the alkalis in the pore solution occurs, pro-
ducing an ASR gel in and around the aggregates. Because aggregates are
uniformly distributed throughout the concrete, cracking typically propa-
gates from aggregate surfaces resulting in cracking throughout the concrete
- this cracking is often referred to as map-cracking. However, the type of
major cracking depends on the type of structure, reinforcing details, and
loading conditions. In addition, because the alkalis are often limited in the
concrete, over time the ASR tends to slow down because the alkalis are
consumed in the chemical reactions. Unlike chloride-induced corrosion
where the propagation is continuous from one surface, ASR propagation
decreases with time and occurs at many surfaces. Cracking due to ASR
typically results not in spalling but in cracking and direct access of aggres-
sive substances to the reinforcement surface. Although limited research has
been performed on how ASR infl uences the capacity of a structure, it has
been established that ASR can result in early corrosion of the reinforce-
ment due to the premature cracking. Unfortunately, limited research has
been performed on the synergistic effects of different deterioration mecha-
nisms and research is sorely needed.
19.2.3 Deterioration and structure service life
Service life is defi ned as the time between when a structure is placed into
service and removed from service. The service life of a structure may be
reduced due to deterioration, variable environmental demands, increasing
load demand, or an event that causes damage to the structure such that it
can no longer be used for its intended purpose. What is important to note
is that with the progress of structural deterioration, structural capacity is
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