Civil Engineering Reference
In-Depth Information
•
A description of preventative measures and repair strategies, and future
trends.
Signifi cant research has been performed to better understand the mecha-
nisms of deterioration. However, limited research has been performed to
assess the structural performance of systems exhibiting damage from these
deterioration mechanisms. This chapter will provide a brief overview of
deterioration mechanisms followed by an overview of the time-variant
performance of bridge structural systems. Although bridge structures were
identifi ed as the structure of choice in this chapter, the process can be
applied to other systems.
19.2 Mechanisms of deterioration
Although the majority of bridges are durable and safe, when bridges are
exposed to aggressive environments, performance and safety of the struc-
tures can be reduced. In addition to the environment, design parameters,
material types, material quantities, and construction practices all impact the
rate at which the concrete or reinforcement can deteriorate. The majority
of deterioration in RC structures results from chemical reactions that occur
between the material and environment or as a result of a phase change in
the material. Corrosion (American Concrete Institute [ACI] 222R-01),
alkali-aggregate (or silica) reactions (AAR or ASR), and sulfate attack
(ACI 201.2R-08) are examples of chemical reactions that occur between a
material and an aggressive compound in the immediate environment.
Freeze-thaw damage (Cai and Liu 1998) and delayed ettringite formation
(DEF) (Scherer 1999; Flatt and Scherer 2008) are examples of a phase
change occurring within the material.
Although sulfate attack could be present in a variety of structures and
environments, it is often associated with structures other than bridges. In
addition, very limited work has been performed on assessing the impact
of sulfate attack on structural performance. Because of this, this mecha-
nism of deterioration will not be addressed herein. The literature does
contain a vast amount of information on the mechanisms of corrosion of
the steel reinforcement and how this process impacts the surrounding
cementitious material (ACI 222R-01; Jaffer and Hansson 2009; Zhang
et
al.
2010). Less work has been performed on assessing the structural per-
formance of corroding RC and PT structures. ASR and freeze-thaw
damage have been identifi ed in a large number of structures and DEF has
been identifi ed far less. As with corrosion, the impact of these deteriora-
tion mechanisms on structure performance has not been thoroughly
investigated. The following sections will provide a general discussion on
the mechanisms of deterioration commonly associated with RC and PT
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