Reinforcing steel in concrete has been used for many years in roads, bridges and other structures to give strength and durability; concrete has only good compressive strength and reinforcing steel gives the tensile strength to the concrete to sustain both the compressive and tensile load, making concrete structures to be used in the common as well as critical areas. Reinforcing steel that was used in structures predominantly is mild steel, which is considerably cheaper than stainless steel, and more susceptible to corrosion leading to the damage of the structures and less longevity. To solve the problem with the use of mild steel in critical areas, such as bridges; stainless steel is used; which has iron as the main constituents along with the chromium as the major alloying element and various grades are manufactured varying the compositions of steel. To reduce the cost of the stainless steel, some compositions like chromium, molybdenum, nickel are varied; especially the nickel is being replaced by manganese, the cost of which is significantly less than that of nickel. The alternative grades of the reinforcing steel that were used for testing the corrosion resistance are mild steel (400), weldable mild steel (400 W) and four stainless steel 316LN, UNS 24100 (Enduramet 32), 2304, LDX 2101; among them 316LN and UNS 24100 are the austenitic steels (Valbruna) and 2304 and LDX 2101 are duplex steels (Outokumpu). The austenitic steels have no ferritic phase which is making austenitic steel more corrosion resistance than the duplex steels which have almost equal parts of the ferritic and austenitic phases. Concrete that is used commonly as the shield for the reinforcing steel providing the environment to passivate the reinforcement. Concrete has the pH of ~13.5 which is the equivalent to the pH of the pore solution. Its strength and curing time varies due to the water cement ratio and composition and also the environment in which it is placed. Good quality concrete has less permeability and fewer cracks thereby limiting the ingress of the de-icing slats to the reinforcing steel and delaying the onset of corrosion. Corrosion of the reinforcing steels was tested in concrete using both an accelerated exposure test and ASTM A 955M standard for cracked prisms to measure the corrosion rate and open circuit potential, which are quantitative measurement for corrosion. It is hoped that the results will provide a guide for the future use of the alternative grades of the reinforcing steel to be used in the concrete. Reinforcing mild steels were compared to determine if there is any advantage in using the more carefully controlled 400W welding grade, rather than the 400 grade. The service life of structures with the 400 grade of steel is well established and so the data from the 400 grade also provided a relative measure of corrosion resistance for the alternative grades of the stainless steel. Microcell corrosion of the reinforcing steel was monitored by the use of the linear polarization and the corrosion potential. The data for show that there is no significant corrosion on any of the stainless steels after 15 months of measurement, whereas both the mild steels embedded in the concrete corroded fully as confirmed by visual observation of the beams after autopsying The autopsied samples were then analysed for chloride content in the concrete adjacent to the reinforcing bars. This was accomplished by titration. The chloride content on the beams with 400 and 400W grades was found to be higher than the beams with the stainless steels, where the percentage of chloride remained almost the same. Macrocell corrosion tests were performed on the ASTM A 955M cracked prisms and showed changes in corrosion current density in agreement with the accelerated corrosion current density of the stainless steels. The only difference was observed in the corrosion potentials of the 400 and 400W steels, which were more negative in the cracked prisms than in the beams. In summary, all the stainless steels showed evident corrosion resistance both in accelerated and ASTM A 955M prisms tests and no sign of corrosion was found in the stainless steels after 400 days in beams and 200 days in prisms. The regular and weldable steels corroded in both tests in agreement with the data present in research.

This thesis discusses the results of an experimental program designed to investigate the effect of corrosion on the behaviour of shear critical reinforced concrete (RC) beams. The results of twenty RC beams (ten deep beams and ten slender beams) are described and discussed. The test variables included: corrosion level (2.5%, 5% and 7.5%) and existence of stirrups (beams without stirrups and beams with stirrups). The feasibility of repairing the corroded shear critical RC beams with CFRP laminates was also investigated. Sixteen specimens were corroded using an accelerated corrosion technique whereas four specimens acted as control un-corroded. Following the corrosion phase, all specimens were tested to failure under three point bending. Test results revealed that the corrosion does not adversely affect the behaviour of shear critical RC beams rather it improves their behaviour. It was found that corrosion changed the failure mode of the corroded beams. The control un-corroded deep beams (beams with and without stirrups) failed in shear-compression failure whereas corroded deep beams (beams with and without stirrups) failed by splitting of the compression strut. The control un-corroded slender beams (beams with and without stirrups) failed in diagonal tension failure whereas the corroded slender beams failed in anchorage failure (beams without stirrups) and flexural failure (beams with stirrups). The analysis of the results showed that corrosion changed the load transfer mechanism and the change of failure mode was associated with the mechanism. The load transfer mechanism changed from a combination of beam and arch action in the control un-corroded deep beams to pure arch action in the corroded deep beams. The load transfer mechanism changed from pure beam action in the control un-corroded slender beams to pure arch action in the corroded slender beams. Two strut and tie models are proposed: one for corroded deep beams and one for corroded slender beams. The ultimate loads of the corroded beams were predicted using these struts and tie models and compared with the experimental results. A very good correlation was found between predicted and experimental results.

Corrosion of the reinforcing steel is a primary deterioration mechanism for reinforced concrete bridges. Heavy use of de-icing salts is believed to be a major contributor in Ontario to severe girder soffit spalling in certain cases. This thesis develops an assessment methodology to evaluate spalled bridges based on ultimate limit states. Specifically, a deterministic program is developed for assessment. It is subsequently compared to laboratory test results and used as a basis for a probabilistic reliability study. A modified area concept is proposed in this thesis to consider the effects of exposing reinforcement at various locations along the girder length. A multipoint analysis program, BEST (Bridge Evaluation Strength Tool), is developed that employs this concept, along with graphical spalling surveys and structural drawings, to evaluate reinforced concrete bridge girders. The program is adapted for a full bridge analysis and to consider the other effects of corrosion, such as bar section loss and bond deterioration. A case study bridge is evaluated to show that the BEST program offers a viable tool for the rapid assessment of spalled bridge girders and to facilitate the prioritization of rehabilitation projects. This evaluation indicates that the spatial distribution of the spalling along a girder, relative to bar splices and laps, has the most significant influence on structural capacity. Single girders show strength deficiencies in flexure and shear due to spalling. In general, the consideration of system effects improves the predicted bridge condition, while considering section loss and bond deterioration has the opposite effect. Laboratory work is used to validate the proposed model and identify a number of areas for future research. The laboratory test results also suggest that the current repair methods are effective in restoring bond and strength. In order to further explore potential uses for the BEST program, modifications are made so that it can be used to perform reliability analyses using Monte-Carlo simulation techniques. A simplified approach for estimating the reliability index as a function of the deterministic resistance ratio is proposed based on the reliability analysis results.

All reinforced concrete (RC) design theories are based on the assumption that concrete exhibits a perfect bond with the steel reinforcement. The bond between steel and concrete is essential to the transfer of the load applied from the concrete to the steel reinforcement. When steel bars are corroded, the concrete cracks, and the strength of the bond between the steel bars and the concrete is decreased. Structures such as bridges and marine structures are prone to corrosion. These structures are usually also subjected to repeated loading. Repeated loading can initiate cracks in the concrete surrounding the steel bars that propagate as the number of load cycles increases leading to the destruction of the concrete-steel interface and slip of the steel bars inside the concrete. The combined effect of corrosion and repeated loading reduces the service life of RC structures. This study investigated the effect of anchorage length and confinement from supports, stirrups and carbon fibre reinforced polymer (CFRP) on the bond behaviour of corroded and uncorroded reinforced concrete beams subjected to monotonic and repeated loading. Fifty-seven large-scale reinforced concrete beams (152*254*2000 mm) were tested for the purpose of this study. The variables were stirrup spacing (75 mm and 150 mm), anchorage length (200 mm, 350 mm and 650 mm), corrosion level (mild corrosion and high corrosion level), repair condition (wrapped or unwrapped with FRP sheets in the anchorage zone) and the fatigue load range. From this study, it was found that the resistance to bond stresses (forces) between the steel and concrete were provided mainly by the concrete keys. The bond stresses increased with the number of the concrete keys engaged. The factors that affected the number of concrete keys engaged were: confinement from the supports, confinement from the stirrups, confinement due to wrapping with FRP sheets and change in anchorage length. Decreasing the stirrup spacing from 150 mm to 75 mm increased the number of concrete keys engaged thus increasing the bond capacity and changed the mode of failure under monotonic loading from splitting to pullout. The beams with the first stirrup spacing (150 mm c/c) when tested under repeated loading failed by bond fatigue while the beams with the second stirrup spacing (75 mm c/c) failed by flexure at the end of a debonded region that started from the support. The failure mechanism is discussed for each case. The change in anchorage length from 200 mm to 350 mm increased the static and fatigue bond capacity of the beams by 60% and 12.5% respectively. The debonding for this group of beams (200 mm and 350 mm anchorage length) subjected to monotonic loading started from the pocket and propagated towards the support while the debonding for the 350 mm anchorage length beams subjected to repeated loading started at the location of a crack that widened while fatiguing the beam and propagated towards the support. The change in anchorage length from 350 mm to 650 mm did not affect the monotonic bond capacity of the beams since in this case, debonding was initiated from the supports and the change in anchorage length had little effect. The confinement with FRP sheets caused the concrete keys at both the top and bottom of the bar to be crushed and increased the bond stress of the wrapped beams. The bond strength of the beams repaired with CFRP sheet was governed by the strength of the FRP sheets for all anchorage lengths and corrosion levels. The CFRP repair of the 200 mm anchorage length set of beams increased the capacity of the uncorroded beams by 80% and the capacity of the corroded beams by about 25% under static and repeated loading compared to the control (uncorroded and unrepaired) beam. The CFRP repair of the 350 mm anchorage length set of beams changed the mode of failure from bond to flexure. The fatigue life for the beams varied linearly on a logarithmic scale with the load range applied with a shallow slope. Corroding the 200 mm anchorage length set of beams to a mild corrosion level decreased their fatigue strength by 34% compared to the control beams. Corroding the 350 mm anchorage length set of beams to a mild corrosion level did not affect the fatigue strength for the single beam that failed in bond. Finally a probabilistic approach was used to allow the design engineers to estimate the design fatigue life for similar beams with 95% probability for a given normalized stress ratio.

Crevice corrosion generally occurs on the crevice surface while the exterior or bold surfaces are not damaged. However, for copper and its alloys, the opposite is true; the bold surface is corroded while the crevice remains relatively corrosion-free. This unique type of corrosion is referred to as reverse crevice corrosion (RCC). In this research, commercially pure copper was chosen as the target metal to investigate RCC. Based on electrochemical measurements and surface analysis, reverse crevice corrosion was found to occur at room temperature. At elevated temperature only uniform corrosion was observed while under a deoxygenated environment, as expected, no corrosion was observed.<p> A multiple crevice assembly and a working electrode were designed especially for this research. Exposure test experiments were first performed at room temperature and 50 ºC. Several types of electrochemical tests were conducted including open circuit potential measurement, potentiodynamic measurement and electrochemical impendence spectroscopy (EIS). Atomic Force Microscopy (AFM) and Raman Spectroscopy were used to analyze the surfaces of the copper coupon.<p>The results of the exposure tests showed that RCC occurred at room temperature, but not at elevated temperature. Only uniform corrosion was observed at elevated temperature and no corrosion was occurred under a deoxygenated environment. It was found, based on the open circuit potential measurement, that the RCC process can be divided into three steps, a uniform corrosion phase, a corrosion slow-down step and a reverse crevice corrosion step. The first two steps can be combined into one phase, incubation phase. This hypothesis is supported with the results from Raman spectra and AFM. The EIS measurements revealed that the diffusion process from bulk solution to copper coupon surface is the rate controlling step for incubation phase and this diffusion process combined with the reduction of Cu (I) oxide in the crevice are the rate-controlling step corresponding to the last step.

Crevice corrosion is a form of galvanic corrosion that occurs when a metal is exposed to different environments. This occurs when the oxygen within the crevice gets depleted, thus acting as the anodic site for metal dissolution reaction. The anodic site thus encourages the migration of Cl- ions into the crevice leading to the development of an aggressive local solution. The acidic conditions present in the crevice reaches a critical crevice solution composition and results in the loss of stability of the passive film which further leads to a rapid breakdown of these films on the metal thus indicating the onset of active corrosion.<p> In this research, it is hypothesized that the onset of crevice corrosion can be detected by measuring the galvanic coupling current between electrodes in a crevice and an external metal surface composed of the same material as the electrodes. To prove this hypothesis an engineered crevice was designed to measure IR controlled crevice currents along the crevice length of AISI 304 stainless steel immersed in a 0.5 M solution and a 1 M NaCl solution. Varying crevice openings were used to determine the effect of crevice gap (G) on the initiation of crevice corrosion and the position of the accelerated attack within the crevice.<p> Multiplexed corrosion potential measurement and galvanic corrosion measurement techniques were used to measure the change in the open circuit potential (OCP) and the galvanic current for the four channels along the crevice length of the galvanic couple. The results obtained from the MGC test for the 100 µm crevice width immersed in 0.5 M NaCl solution showed good results with high anodic current at approximately 1 cm from the crevice mouth. This finding was in close agreement with the peak pH value observed at the position closest to the crevice mouth in the work of Alavi and Cottis (1987) and the model prediction of Kennell et al. 2009. However, for test samples with crevice width ≥ 200 µm, there was no initiation of crevice corrosion and the results obtained were discarded. The Linear polarization resistance scan and Potentiodynamic polarization scan carried out along the crevice to measure the polarization resistance, Rp , and to obtain the region of passivity along an AISI 304 SS crevice did not yield good results. Low corrosion rate in the range of 0.06 mm/yr was calculated for the AISI 304 stainless steel crevice.

Automobile components are often exposed to aggressive environments as a result of aqueous salts from the road coming into contact with unprotected steel. This situation greatly reduces both the life and the appearance of the affected parts. Ultra-high strength steel parts are suspected to exhibit poor corrosion-fatigue properties and be more susceptible to corrosion in general. In this study, the effect of strength level on the decrease in fatigue life of AISI 4130 steel when exposed to an aqueous salt solution is quantified. The observed mechanical properties including corrosion-fatigue behavior are examined with consideration to different microstructural characteristics resulting from heat treatments to the steel. The hardness and tensile properties of the test material were characterized before fatigue testing. Fatigue tests were completed in both air and salt solution to determine the effect on fatigue life of the latter environment. Following fatigue testing, the fracture surface was examined using a scanning electron microscope (SEM) to determine the failure mode. Six strength levels of AISI 4130 steel were investigated ranging from 837 to 1846 MPa (121 268 ksi). The frequency of loading used for corrosion-fatigue tests was 1 Hz and the stress ratio for each test was constant at R = 0.1. The corrosion-fatigue tests consisted of the specimen being submerged in an aqueous solution of sodium chloride, calcium chloride, and sodium bicarbonate and fatigued until failure. The solution was maintained at room temperature with constant aeration to ensure constant oxygen levels. The parameters of interest were the applied loads and the cycles to failure. There were four primary findings of the study. First, decreases in fatigue life of the material caused by the corrosive environment ranged from 100% in the lowest strength level to 190% in the higher strength levels. This result showed that higher strength in this steel corresponds to increasing detriment to fatigue life when the material is exposed to an aqueous salt environment. Second, evidence was found that the salt solution lowered the fatigue limit for each strength level studied in this material. All specimens that were tested in the corrosive environment failed in less than 150,000 cycles, while some specimens fatigued in the air environment experienced run-outs at over 106 cycles. Third, the decrease in fatigue life was attributed to the presence of martensite in the structure of the steel. It was noted that the higher the martensite content, the larger the decrease in fatigue life when exposed to the corrosive environment. Finally, the fracture surfaces of fatigued specimens revealed that a similar cracking mode was present for each strength level in both environments. Enhanced crack initiation was, therefore, assumed to be the cause of the decrease in fatigue life between the air and aqueous salt environments.

No description available.

Wreckage of ‘Carnauba’, a 1930s vintage Sikorsky S-38 aircraft, a beloved icon of SC Johnson's early history, was found on July 5, 2000, in seawater off of an Indonesian island of West Irian Jaya. The company decided to recover this aircraft from seawater, conserve it, and display it in its museum, as part of their rich heritage. The objective was to study the aluminum alloy used on the aircraft for its chemical and mechanical properties, suggest the corrosion mechanism of aluminum alloy 2024 in seawater, and recommend preservation methods for the same. Chemical analysis performed on the samples collected from the site revealed that copper was the primary alloying element. Copper is responsible for increasing the strength. However, copper is also the reason for pitting corrosion of the aluminum alloy, causing material loss and reducing the structural stability of the wreckage. Copper forms intermetallics with other elements, such as magnesium and aluminum, and is distributed in the aluminum matrix heterogeneously. In order to study the corrosion mechanism of aluminum alloy 2024, it was subjected to potentiodynamic tests in sodium chloride solution. In the presence of an electrolyte like seawater, the difference between the potentials of these intermetallics and the surrounding aluminum matrix creates a galvanic cell. The galvanic cells serve as sites for localized corrosion. Chloride ions are responsible for pitting of alloy 2024. A pitting potential of around -600mV was observed when sodium chloride was used as an electrolyte. The average corrosion rate measured for wrought aluminum alloys was around 0.05 mm/year. The thesis provides guidelines or recommendations for the procedure to be followed in recovering aircraft from seawater, and retain it in its as found condition. Recommendations about various measurements like pH, dissolved oxygen, salinity, pressure, temperature, and velocity need to be taken and the visual assessment needs to be done before the aircraft is hauled from the seawater were specified. After the aircraft has been recovered, recommendations for handling, cleaning, and prevention of corrosion using coatings such as carnauba wax and inhibitors such as chromates, have been stated.

The effect of corrosion on a single-bent, reinforced concrete (RC) bridge subject to seismic loading is the primary focus of this research. This work attempts to determine the effects of decreasing rebar diameter and concrete cover spalling on the strength and stiffness of the RC bridge. The application of these results to the field of historic preservation will also be explored. Through the use of static and dynamic analyses, this research shows that the effects of corrosion only have a slight influence on the seismic fragility of the RC bridge. The loss of three inches of concrete cover from the bridge column is shown to have a greater effect on the strength and stiffness of the bridge than decreasing the rebar diameter by 10%. The deformation capacity and demand both increase for bridges with reduced reinforcing steel and concrete cover; however, the capacity increases to a greater degree than the demand. The seismic fragility of the bridge based on deformation criteria is greatest for the pristine structure, and it decreases as the level of damage increases. Future work should include verifying the hysteretic behavior by accounting for reinforcement slip caused by a loss of bond.