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Structural assessment of "d" regions affected by premature concrete deterioration : technical report.
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2015-03-01
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Abstract:The current study is a continuation of the earlier study that investigated the effects of Alkali Silica Reaction (ASR) and Delayed
Ettringite Formation (DEF) induced deterioration on the D-Regions of structures. Of the four near full-scale C-Beam specimens that
were constructed, and conditioned over time as part of the earlier study, the last specimen (Specimen 3), which was field conditioned
through the Texas heat along with supplemental water for a period of five years, is the main focus of this study. With time, additional
cracks caused by ASR/DEF swelling were observed in addition to the load induced cracks. Based on the deterioration data collected
and observations made on Specimen 3, it was classified to show heavy damage due to ASR/DEF deterioration. The experimental
test of Specimen 3 which resulted in a brittle shear failure through the beam-column joint, showed a similar failure mechanism to
the other three C-Beam specimens. The heavy deterioration caused by ASR/DEF deterioration also did not seem to have any effect
on the load carrying capacity of the specimen. However, the response of the specimen was considerably stiffer and less ductile than
the earlier tested C-Beam specimens with no, slight, and moderate amounts of deterioration. This is due to the restraint offered to
ASR/DEF swelling strain by the reinforcement, which causes tensile strains in the reinforcement. This effectively put the concrete
under a state of active prestress. Although no signs of corrosion are observed in the specimen during the deterioration phase, in terms
of concrete cover spalling or rust stains in concrete, a considerable amount of corrosion was observed on the reinforcement bars once
the cover concrete was removed.
A minimalist semi-empirical analysis technique is developed to model the expansion strains caused by ASR/DEF expansion
in reinforced concrete. The proposed model takes into account the effects of compressive and tensile prestrains on the expansion
strains caused by ASR/DEF, in addition to the daily variations in temperature and humidity. This enables the model to capture the
expansion strains in reinforced concrete structures that are exposed to environmental conditions. The model is validated and applied
to simulate the expansion strains observed for the C-Beam specimens. Considering the complex nature of the ASR/DEF phenomena,
the nature of the structure considered, and the variability in the field recorded data, the model simulates the expansion strains quite
well.
The Compatibility Strut-and-Tie Modeling (C-STM) technique, which was developed and verified in Phase I of this report,
is used to model the force-deformation behavior of C-Beam Specimen 3. The expansion strains that are obtained from the ASR/DEF
model is used to compute the prestress loads to be applied in the C-STM technique to account for the effects of ASR/DEF expansion
in the model. The C-STM simulates the overall force-deformation and the internal behavior of the structure quite well.
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