Reinforced concrete--Corrosion

Steel reinforced concrete beams were placed in contact with
seawater in a state of accelerated corrosion, for varying
periods of time. Some of them were simultaneously monitored
for acoustic emission and the results were analyzed to
evaluate the effectiveness of acoustic emission as a
non-destructive monitor of corrosion induced damage. It was
shown that, in a laboratory environment, counts are good
indicators of the extent of corrosion damage. A review of
acoustic emission monitoring techniques and theoretical
background is included. The concrete beams were tested for
flexural strength after being corroded. Reduction in rebar
section was found to have a very good correlation with
da mage. An attempt was made to predict remaining life of
the beams based on data obtained from the tests.

Measured values of attenuation with distance, amplitude distribution,
and propagation velocity of acoustic emissions associated with
embedded metcil corrosion induced cracking in a concrete slab are
presented. An extensive review of acoustic emission signal processing
techniques and theoretical background material is also included.
The study points out how attenuation and propagation velocity of the
acoustic emission signal affects various signal processing techniques
and verifies an amplitude distribution spreading rrodel. The need
for further defirlition of attentuation values caused by fluid loading
of the concrete surface is also discussed.

In this investigation acoustic emission techniques were employed to
detect deterioration of reinforced concrete. As a result of various
laboratory tests, acoustic emission activity was found to be due to
development of cracking only. Acoustic emission techniques were able
to locate cracks in a specimen by linear location. Various acoustic
emission parameters such as amplitude, signal shape and frequency
were also analyzed and discussed. It was concluded that acoustic
emission techniques provided a feasible method for detection of deterioration
and cracking of steel reinforced structures in laboratory
studies as well as in a field environment.

Investigation of concrete-rebar interface conditions was
conducted for the purpose of identifying governing parameters
of the concrete cracking process in seawater. Experiments
included an examination of chloride ion penetration,
concrete pH as a function of metallic chloride concentration,
and pH distribution within reinforced, impressed current
specimens. Metal-concrete systems investigated included
iron, molybdenum, cadmium, zinc, aluminum, copper, and
nickel. Simplified models of the rebar corrosion process
are presented in conjunction with electrochemical analysis
of the projected interface chemistry. Results indicated
that chlorinities greater than seawater concentration may
occur as a result of potential gradients in reinforced concrete.
Laboratory simulations of interface chemistry indicated
that metallic and chloride ions may produce an acid
pH in concrete solutions when present in sufficiently high
concentrations. Heasurements of pH on the fracture face of
impressed current corrosion specimens indicated localized
acidic conditions can develop.

The objective of this investigati.on was to contribute to
the determination of a suitable metallic coating for steel
reinforcement in concrete exposed to a marine environment
and possibly to stray current. Concrete specimens embedded
with steel, aluminum, cadmium, copper, molybdenum, nickel,
and galvanized steel were exposed to sea water. Direct
current was impressed on these to accelerate corrosion of
the reinforcement so that cracking of the concrete could be
observed within the time limit of the investigation. Aluminum,
cadmium, copper, and nickel were found to have no beneficial
effect on concrete cracking as compared to steel. In
addition, no correlation between oxide-metal volume ratio
and concrete time-to-cracking could be observed. It was
found that corrosion of molybdenum has little or no tendency
to crack concrete and its corrosion potential and active
behavior approximates that of steel, indicating it may be
an excellent coating.

This study employed half-cell potential (Eoc), polarization resistance (PR) and galvanic current tests to explore effects of surface condition and steel reinforcement type on corrosion initiation in mortar. A low impurity steel plate and #10 grade 60 rebar were used. Four surface conditions (as-received, atmospherically rusted, #240 SiC paper polished, and #500 SiC paper polished) were employed. Cyclic wet and dry exposure of specimens in 15% NaCl solution was conducted. Half-cell potential measurements showed that the corrosion probability of specimens with as-received and pre-rusted surfaces was lower than that of specimens with a polished surface. However, the PR and galvanic current tests indicated higher corrosion rate for specimens prepared with atmospherically rusted and as-received steels. Good agreement was found between results of the polarization resistance test and galvanic current measurements. There is a lack of correlation between half-cell potential and corrosion rate.

The purpose of the thesis is to determine and compare the performance characteristics of marine piles corroded by chloride diffusion and repaired by several different methods for both uncracked and cracked concrete and to determine their structural integrity. The long-term objective is the comparison of the analytical values with those from an on-going experimental evaluation. The time for chloride concentration reach the threshold value that initiates corrosion in the reinforcement has been determined by Fick's law, extended to 2-D and 3-D chloride diffusion, for (a) uncracked concrete, and (b) for cracked concrete with the Simplified Smeared Approach (SSA). The structural integrity of the concrete circular pile is compared before and alter repair, by (a) finite element modeling using ANSYS software with the maximum deflection, and (b) beam strength analysis to find the moment capacity for cracked and ultimate conditions. The overall findings indicate the adequacy of the repair procedures.