Chloride Induced Pitting Corrosion-Fatigue in Reinforced Concrete Structures
Date
2017-09-18
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0002-0054-2614
Type
Thesis
Degree Level
Doctoral
Abstract
There is currently a general agreement that the long-term performance of many civil infrastructure
facilities, such as bridges, tunnels, harbor facilities, nuclear power plants etc. is strongly dependent,
not only on mechanical loading, but also on the harshness of their service environment. CorrosionFatigue (CF) is a damage mechanism commonly found in many Reinforced Concrete (RC)
structures (bridges, harbor structures, oil platforms, etc.) exposed to variable loading and a
corrosive environment. CF is a synergetic phenomenon between corrosion and fatigue wherein the
damage caused by the simultaneous action of both mechanisms is usually greater than when either
corrosion or fatigue is acting alone. Recognizing that aging of these structures may adversely
impact their ability to fulfill their intended function in the future, some strategies have been
developed for predicting their service life and for mitigating the effects of aging on their
performance. Despite its practical importance, only a relatively small number of studies have been
carried out on the CF of reinforced concrete structures. Indeed, most durability studies in RC focus
on either corrosion alone or fatigue without corrosion. In the few instances where CF was
considered, oftentimes only RC structural elements, such as beams, were tested. Although
providing important information about the overall CF behavior of this kind of structure, such tests
also make it virtually impossible to extrapolate the application of those results to other structures
or loading/exposure conditions.
This study proposes a new approach for assessing the CF of reinforced concrete structures that
relies on a realistic constitutive characterization of CF of steel reinforcement in simulated concrete
pore solutions. The novelty of the proposed approach resides in its ability to accelerate both
corrosion and fatigue loading simultaneously and independently so that a given field condition can
be represented without favoring one mechanism over the other. Given the difficulty in accelerating
corrosion to the required values to match the acceleration of fatigue loading, oftentimes the
acceleration factor for fatigue is much higher than the one used for corrosion, making the test
results not very representative of the field conditions.
The research objectives of this study were divided into two main sequential stages. In stage one,
the corrosion-fatigue behavior of carbon steel reinforcement is characterized as a material operating in a chloride-laden simulated concrete pore solution in a way that is compatible with two
widely used fatigue analysis approaches (S-N curves and Fracture Mechanics). A combination of
pore solution chemistry and an electrochemical method is used in this study to develop a novel
corrosion fatigue cell that can accelerate, independently, both corrosion and fatigue so that the
degradation rates are representative of typical in-service conditions. The simulated pore solution
chemistry is chosen so that it is representative of typical concrete environments that favor pitting
corrosion in the presence of chloride ions. The electrochemical method is used to overcome the
limitations of the maximum corrosion rates that can possibly be achieved through the chemical
composition of the simulated pore solution alone, so that CF tests (representative of field
conditions) can be carried out within a reasonable time frame. In stage two, the ability of the two
constitutive models, developed in stage one, to predict the fatigue life of reinforced concrete beams
in a corrosive environment is assessed, as an example of a structural component.
The results of the model predictions, for both approaches (S-N curves and Fracture Mechanics),
were compared with the experimental results from an independent set of RC beams tested under
corrosion-fatigue. The results show that both methods can be used to estimate the service life of a
RC structure subjected to corrosion-fatigue. It is worth mentioning that the S-N curve approach
provided more precise estimations than those provided by fracture mechanics, with standard errors
ranging from 9.0% to 23.0%, instead of ranges between 26.7% and 54.2%, respectively. However,
although the estimation of the fracture mechanics approach shows a higher error range, this method
provides more insight into the evolution of damage in the rebar over time. The fracture mechanics
model accounts for the four main stages of the metal degradation process: pit nucleation and
growth, pit-to-crack transition, crack growth state, and ultimate fracture failure. The results
indicate that the pit nucleation and growth stage occupies over 79.9% of the total service life in
the prediction of the tested RC beams under CF. This result suggests that unstable crack
propagation would not take place before the occurrence of extensive corrosion in the material. In
other words, corrosion plays a more significant role than usually reported in the corrosion fatigue
life of RC under realistic conditions.
Description
Keywords
corrosion-fatigue, reinforced concrete
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Civil and Geological Engineering
Program
Civil Engineering