Evaluation of Active and Passive Thermography for Rapid Detection and Characterization of Concrete Infrastructure Defects, Damage, and Deterioration 3
Can active heat-pulse or passive thermography be implemented in a manner that is technically and economically feasible for rapid and effective detection and imaging of concrete structure defects/damage/ deterioration in a field-scale implementation scenario? What is a reasonable spatial resolution and reasonable depth of investigation (DOI) limitation for thermal tomography on concrete? What are some of the main limiting factors in DOI? Damage and deterioration of concrete structures poses several safety and economic risks related to reclamation's aging critical infrastructure and is oftentimes very difficult and costly to assess comprehensively using typical visual inspection and invasive techniques. Rapid and effective means to detect and characterize concrete structure damage/ deterioration more comprehensively is needed by reclamation and other related entities.
Need and Benefit
Reclamation has several large concrete dams and other large concrete infrastructural components that are considered
to be "high-risk" due to their critical functions and locations relative to large downstream population centers (e.g., large
economic losses and loss of life for downstream populations in the event of a catastrophic failure). Many of these
high-risk structures are in various states of deterioration, increasing the probability of failures in certain plausible
Dam safety and risk management activities often involve probabilistic seismic hazard analysis (PSHA) and dynamic
wave propagation modeling (e.g., using LS-Dyna) to better predict and understand realistic potential seismic loading
and related chances of various failure modes of large concrete structures. Each of these components to risk
management requires the input of various physical properties distributions, including seismic wave propagation
velocities, static and dynamic elastic moduli, and fundamental and higher modes of a given structure's vibration (e.g.,
the resonant frequencies of complex structures). These key structural properties often require a gross estimate of
mass density or the location and geometry/severity of various types of concrete defects, which are typically very
difficult and expensive to quantify within these large structures (oftentimes requiring extensive drilling/coring efforts or
Reclamation and other federal/state dam safety/risk management groups are faced with the challenge of assessing
and quantifying risk related to static and dynamic loading of large water impoundment structures, including earthen
and concrete dams. Risk analysis efforts include estimating the probability of catastrophic structural failures during
large amplitude "shaking" of these structures and their foundations during and following an earthquake or other
strong-motion event. In the case of rigid concrete structures, distributed defects such as alkali-silica reaction (ASR)
and cyclical freeze-thaw deterioration processes exacerbate probability of certain failure modes. Additionally, poor
bonding of adjacent concrete pours ("bad lift-lines"), concrete placement issues resulting in honey-combing and poor
aggregate bonding, delaminations from underlying reinforcement, or the development of localized cracking due stress
and strain forces within these rigid structures (e.g., due to differential settlement processes, hydrostatic loading or
differential curing and thermal expansion/contraction) can increase the probability of certain failure modes occurring
during dynamic loading.
If deemed a successful approach to detecting and mapping/imaging concrete defects, this technology could be used
to more comprehensively assess the state of disrepair of critical concrete infrastructure and high-risk
structures/miscellaneous structures, and help to guide and optimize repair and mitigation efforts. Additionally, the
results of application of this technology could help to guide efficient and intelligent design and placement of more
costly and invasive investigations, including the placement of coreholes along the crest of concrete dams, or across
the vertical/sub-vertical faces of concrete structures.
The location, spatial extent and severity of concrete defects are usually poorly understood, and typical assessment
methods are often conducted "blindly" (e.g., random placement of coreholes, without the use of additional information
or prior knowledge of defect location/severity). As a result, there is the ever-present chance of underestimating the
severity of damage to these structures and the subsequent overly liberal estimate of safety factors/risk.
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