No description available.

Thesis (M.S.)--University of Hawaii at Manoa, 2006. / Includes bibliographical references (leaves 113-114). / xi, 132 leaves, bound ill. 29 cm

No description available.

Master of Science

In 1989, the specific ion electrode was identified as the best field method available to assess the chloride content of powdered concrete samples. Since the initial investigation, the manufacturer of the packaged device has altered the product. The alterations presented a equipment difference, as well as an increase in cost. To eliminate the problem of random manufacturer alternations, a generic method was developed for evaluating the chloride contents of concrete with the specification electrode. The method outlined the required equipment, the proportioning of the calibration solutions, the proportioning of the concrete digestion solution, and the measuring procedure. The developed method eliminated the problems of the digestion reaction temperature and the measurement inaccuracies of the higher chloride contents by diluting the measured concentrations. The testing procedure was validated for field application by measuring the chloride contents of concrete samples from four state bridge structures. The analysis of operator variance proved the method was applicable to any operator capable of following the procedure. / Master of Science

Concrete provides a nearly perfect environment for corrosion protection of steel; However, the use of de-icing salts on the highway system has accelerated the deterioration rate of bridge decks in the snow belt. In 1981, over 100,000 bridges were reported to be structurally deficient, and the estimated cost of repair was placed at $93 billion. Concrete specimens, 1 ft. x 1 ft. x 4 in., containing four pieces of steel reinforcing bars, were prepared. In a first time, five specimens with different rebar networks were cast in order to study the effects of the rebar network on corrosion. Half-cell potential measurements were used to monitor the corrosion behavior of each specimen. In a second time, calcium nitrite, monofluorophosphate and sodium borate were evaluated for their capacity to control corrosion. The various corrosion inhibitors were tested either externally (in the test solution), internally (as a concrete admixture). The specimens were exposed to alternate complete immersion in a 6 wt% sodium chloride solution, plus eventual addition of corrosion inhibitor, for 3 days and 12 hours of drying at 110°F. The effects of corrosion inhibitors were evaluated using half-cell potential measurements and Electrochemical Impedance Spectroscopy (EIS) measurements. The EIS data were analyzed through a computer assisted EIS data analysis system. This allowed for circuit modeling of the corrosion mechanisms and evaluation of polarization resistance values for the different specimens. In both phases of this work, chloride concentration profiles as function of depth were determined. The half-cell potential measurements in complete immersion were found to give an average over the length of bar or electrically connected bars. The corrosion inhibitors applied internally were found to reduce corrosion better than corrosion inhibitors applied externally. It was shown that chloride concentration is not the only parameter controlling corrosion initiation. / Master of Science

The FDOT has been using supplementary cementitious materials while constructing steel reinforced concrete marine bridge structures for over 3 decades. Previous findings indicated that such additions in concrete mix makes the concrete more durable. To better understand corrosion propagation of rebar in high performance concrete: mature concrete samples that were made (2008/2009) with Portland cement, a binary mix, a ternary mix and recently prepared (April 2016 with 50% OPC + 50% slag and 80% OPC + 20% Fly ash) concrete samples were considered. None of these concretes had any admixed chloride to start with. An accelerated chloride transport process was used to drive chloride ions into the concrete so that chlorides reach and exceed thechloride threshold at the rebar surface and initiate corrosion. Electrochemical measurements were taken at regular intervals (during and after the electro-migration process) to observe the corrosion propagation in each sample. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2017. / FAU Electronic Theses and Dissertations Collection

M.S.

Corrosion of concrete sewer crowns will cost the County Sanitation Districts of Los Angeles County approximately $150 million for repairs to their deteriorating sewage system. Other parts of the country are experiencing similar problems. Crown corrosion is induced by microbial oxidation of reduced sulfur to sulfuric acid, which attacks the concrete. Bacteria, of the genus Thiobacillus are generally responsible for catalyzing these reactions. Thiobacillicollected from sewers were used to establish stoichiometry and biochemical aspects of sulfide oxidation. Metals inhibition was studied among the same cultures. Thiobacilli collected from extremely corroded sewers possess a greater tolerance for metals than those from lightly corroded areas. Acidophilic isolates grow at greater rates and oxidize sulfide more efficiently than non-acidophiles. Chemical inhibitor studies indicated that S(-II) oxidation is tightly linked to respiration by T. thiooxidans. It is doubtful that initial steps in bacterially catalyzed S(-II) oxidation are linked to oxidative phosphorylation.

Chemical inhibition of acid production by acidophilic thiobacilli was tested using a variety of metals and chelators (alone and in combination) including Hg(II), Ag(I), Co(II), Mo(VI), Cu(II), Zn(II), Cd(II), EDTA and NTA. When tested individually, Hg(II) and Ag(I) showed toxic effects at concentrations of 10-5 M and below; Cd(II), Zn(II) and NTA were noninhibitory at millimolar concentrations. Combination experiments showed both synergistic and antagonistic effects on chemical toxicities. Antagonism was apparent in experiments involving Cu(II)-EDTA, Cu(II)-Fe(III) and Cu(II)-Co(II). Synergism was apparent in experiments involving simultaneous addition of Mo(VI), Cu(II), Co(II) and Zn(II). In general, inhibitors either completely blocked or delayed the onset of acid production. In those cases where delayed reactions were observed, acid production began following an acclimation period on the order of days to weeks. Acclimation and metals speciation experiments suggest that adaptation events are due to biologically dependent changes in inhibitor speciation.