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OCR for page 1
SUMMARY
An analysis and compilation ofthe available information on the durability of precast segmental
bridges was conducted, with emphasis on those structures in the United States and United Kingdom
that utilize grouted internal tendons. The focus in terms of durability was on the corrosion
performance of grouted internal tendons.
A comprehensive literature search, a nationwide survey in the United States, and personal
contacts indicated there have been significantly more reported problems with precast segmental
bridges, and post-tensioned bridges in general, in the United Kingdom than in the United States. The
corrosion-induced collapse of two precast segmental structures in addition to reported problems with
grouted post-tensioning led to a moratorium on grouted post-tensioned construction in the United
Kingdom. Although the ban on grouted post-tensioned structures has been lifted, the ban on precast
segmental construction is still in effect to date. In contrast, there have been no reported problems with
durability of precast segmental bridges to date in the United States and only a few problems with
grouted post-tensioned bridges.
The available information indicates that, although there has been durability problems with
precast segmental bridges, the overall number of problems are few. Moreover, the corrosion problems
encountered in the United Kingdom were due to poor design choices and poor quality construction
rather than a significant intrinsic susceptibility to corrosion.
Although reported problems have been few, especially in the United States, it is important to
keep in perspective that there has not been exhaustive field investigation of the corrosion performance
of precast segmental bridges; most of the reported information is based on simple visual inspection.
While non-destructive testing (NDT) can provide information on the condition ofthe grout and the
prestressing steel, current NDT options vary in comprehensiveness, versatility, and cost. There is a
need for better NDT evaluation and inspection techniques.
1
OCR for page 2
A current on-going laboratory study has indicated that properly constructed precast segment
joints with internal tendons are corrosion resistant, especially match-cast epoxy joints with complete
encapsulation of the prestressing steel in a high quality grout. Other related research on the durability
of post-tensioned bridges have shown good corrosion resistance of properly designed and constructed
post-tensioned bridge elements.
Since both research and experience indicate that durability problems are due to poor design
choices and construction execution, rather than intrinsic problems with precast segmental construction,
it is highly probable that properly designed and constructed precast segmental bridges are durable.
In order to ensure good future performance of precast segmental construction in the United
States, AASHTO should adopt the AASHTO Guide Specifications on the design and construction of
precast segmental bridges as fully enforceable specifications. Thin mortar joints should be specifically
precluded and match-cast dry joints should not be allowed in any corrosive environment. Additionally,
more stringent and comprehensive grouting specifications need to be adopted. Additional research
should be performed on the durability of segment joint and anchorage details and on non-destructive
testing and evaluation techniques. Also, a reasonably comprehensive field testing and evaluation study
should be conducted on a few of the oldest segmental bridges in the United States that are exposed
to a corrosive environment to gain additional insight into the performance and long-term durability of
precast segmental bridges that heretofore has mostly been garnered by visual inspection.
2
Representative terms from entire chapter:
segmental bridges
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