Rust Products Research Articles

Effects of Reinforcement Corrosion on the Performance of RC Frame Buildings Subjected to Seismic Actions

AbstractCorrosion of reinforcing bars is a common deficiency for existing RC buildings, which may have significant adverse effects on seismic performance of those buildings. The main effects of corrosion of reinforcing bars are strength loss as a result of reduction of the effective cross-sectional area of the bars, reduced bond strength between concrete and bars as a result of the increased volume of the bars because of rust products, and reduced elongation capacity of the bars as a result of the concentration of plastic deformations at sections of corrosion pits. The last item (concentration of plastic deformations of reinforcing bars only at the most heavily corroded sections rather than occurring all through the potential plastic hinge length) has a very remarkable adverse effect on the displacement capacity of existing buildings. It is known that the displacement capacity is as important as strength, particularly for the buildings that are designed to exhibit ductile behavior during earthquakes. In t...

Which Rust Deposition Model Should Be Used in Predicting Concrete Cover Cracking due to Reinforcement Corrosion?

The critical amount of corroded steel that causes concrete cover cracking can be readily calculated based on thick-walled cylinder theory. However, the results may vary significantly depending on how the rust deposition is considered. There are several rust deposition hypothesis proposed in the literature for modelling concrete cover cracking of RC structures due to reinforcement corrosion. Among them, three are considered representative ones and have been widely cited in the literature. They are: (i) assumes a certain amount of rust product carried away from the rust layer and deposited within the open cracks proposed by Pantazopoulou and Papoulia; (ii) assumes all of the rust products build up around the bar and all of them are responsible for the expansive pressure proposed by Bazant; (iii) assumes certain amount of rust products deposited into a porous zone around the bar/concrete interface proposed by Liu and Weyers. In this paper, all three rust deposition hypotheses were examined for the critical amount of corrosion to induce cover cracking. When compared to the test data available from the literature, it showed that the porous zone model proposed by Liu and Weyers gives the best predictions. Thus it may be concluded that assuming a porous zone around the steel/concrete interface would be reasonable and may be adopted in developing concrete cover cracking predictive model.

Effect of the Chloride Content on the Rust Layers of 09CuPCrNi

The accelerated wet-dry cyclic corrosion tests at different chloride content have been carried out on 09CuPCrNi. The morphology and composition of the rust products have been investigated. The rust layers were composed of the dense inner layer and the loose outer layer. The rust layers were mainly composed of magnetite (Fe3O4) and maghemite (γ-Fe2O3). The rust phase of -Fe2O3 was detected in higher amounts in the rust layers of 1% wt NaCl which resulted in the rust layers much denser. The alloying elements of copper, chromium and phosphorus enriched in the rust layers are helpful to the formation of γ-Fe2O3. The protective denser rust layers play an important role in corrosion resistance of the steel.

The effects of corrosion on 45-year-old pre-stressed concrete bridge beams

There have been few reports of structures that could be examined in detail for long-term behaviour and performance. One opportunity arose in 2002 when the Sorell Causeway bridge, a 45-year-old, 457 metres long, 34 span, pre-stressed concrete bridge in Tasmania, Australia, was demolished. This followed concerns about its safety in the light of the increasing size and frequency of occurrence of longitudinal cracks in the webs of the beams, the cracks appearing to follow the trajectory of the post-tensioning tendons. Corrosion was suspected. Pre-demolition testing had not provided sufficient information for estimates to be made of the remaining capacity of the bridge. After demolition, three bridge beams were selected for very detailed evaluation. The load capacity of the most severely damaged beam was only half that of the apparently sound beam. It failed catastrophically. The more seriously damaged beams showed severe loss of ductility. Progressive failure of the strands in the tendons was recorded in each case. The corrosion of the conventional reinforcement was consistent with expectations. However, some of the pre-stressing strands showed severe localised corrosion with cross-section losses between 75% and 100% but with little evidence of conventional oxidation rust products. Green rusts and ferrous chlorides were observed. The apparently sound beam also showed severe localised corrosion of strands.

Modeling the Structural Effects of Rust in Concrete Cover

Vast governmental budgets are spent annually to face corrosion problems of steel reinforcement in concrete bridges attributable to the extensive use of deicing salts. Corrosion controls the lifetime of a bridge, which has two distinct periods. During the first period, chlorides diffuse through the cover. When sufficient chlorides are formed at the rebars, corrosion initiates. This marks the start of the second period, during which rust with higher volume to bare steel is produced. The rust puts pressure on the cover, which finally leads to cover spalling. In this paper, a model is developed to determine the time span of the second period. The model includes a volume compatibility condition that allows for the proper introduction of compaction of all materials that contribute to cover spalling, including the rust. A new condition for marking failure of the cover is also established, based on fracture mechanics and strain energies. Finally, a new formula is proposed for the rate of rust production, which allows for the constant rust production at early and nonlinear diffusion dependant rates at latter stages of corrosion. DOI: 10.1061/(ASCE)EM.1943-7889.0000215. © 2011 American Society of Civil Engineers.

Environmental effects on cover cracking due to corrosion

This paper examines the environmental conditions under which the time to cracking of concrete, due to pressure caused by rust production on the surface of steel bars, is short. To determine this time, volume compatibility is assumed, which allows for compaction of all materials affected by the pressure, including the rust itself. A fracture mechanics concept is also used to signal cover failure. The model reveals that time-to-cover-cracking is a function of the rust production and the strength of the system to resist the resulting pressure. It is found that the highest corrosion rates are towards the end of autumn and the beginning of spring, when humidity reaches relatively high values with moderate temperatures. On the other hand the highest resistance of the system to corrosion production is during summer, since the humidity is low. In addition, rust pressure drops during summer due to creep; water moves out of the concrete which also deforms, giving more space into which the rust can expand. Structures exposed to humid summers would suffer from high rust production and rapid cover spalling. The model can assist in the decision-making process to identify when a bridge is more likely to corrode, which could indicate that new materials, like fibre reinforced polymers might be the most suitable design solution despite their higher initial cost.

Bond analysis of corroded reinforced concrete beams under monotonic and fatigue loads

Abstract This study investigated the fatigue bond behaviour of corroded steel reinforced concrete beams. Nine beams (152 × 254 × 2000 mm [6 × 10 × 78.74 in.]) were constructed and tested. Bond failure occurred in all the beams. The variables in this test series were: the type of load applied (monotonic or repeated loading), the repeated load range, whether the reinforcement inside the beam was corroded or not, and whether a carbon fibre reinforced polymer (CFRP) repair method was used or not. The fatigue life of the beams varied linearly with the range of applied load with a very shallow slope. Corroding the beams to a low corrosion level decreased the fatigue bond strength by about 30%. Corrosion caused the concrete in between the lugs of the reinforcing bars to be partially crushed due to the formation of the rust products from the corrosion process. This reduced the strength of the concrete keys and increased the rate of slip in the bar under repeated loading.

Mechanical properties of the rust layer induced by impressed current method in reinforced mortar

This paper describes the mechanical effects of rust layer formed in reinforced mortar through accelerated tests of corrosion. The morphological and physico-chemical properties (composition, structures) of the corrosion system were characterized at different stages by using optical microscope and scanning electron microscope coupled with energy dispersive spectroscopy. The corrosion pattern was mainly characterized by a rust layer confined at the interface between the steel and the mortar. Expansion coefficient of rust products was determined from the rust thickness and the Faraday's law. Furthermore, in order to understand the mechanical effects of corrosion on the damage of mortar, displacement field measurements were obtained by using digital image correlation. An analytical model (hollow cylinder subjected to inner and outer pressures) was used with a set of experimental data to deduce the time of cracking and the order of magnitude of the mechanical properties of the rust layer.

Electrochemical studies on the alternating current corrosion of mild steel under cathodic protection condition in marine environments

Alternating current (AC) corrosion of mild steel in marine environments under cathodic protection (CP) condition was studied. Electrochemical studies at the two protection potentials namely −780 and −1100 mV versus SCE were examined by different techniques. DC polarization study was carried out for mild steel in natural seawater and 18.5 g/L NaCl solution to evolve corrosion current density. The corrosion rate determination, pH of the end experimental solution and surface morphology of the mild steel specimens under the influence of different AC current densities were studied. The amount of leaching of iron into the solution was estimated using inductively coupled plasma spectrometry. All these techniques revealed that AC influences the corrosion of mild steel in the presence of marine environments even though CP was given. Surface micrographs revealed that spreading of red rust products noticed on the mild steel surface. At −780 mV CP, red rusts are visually seen when the AC source was above 10 A/m 2 in both the media but red rusts are appeared after 20 A/m 2 in the case of −1100 mV CP. Weight loss measurements coupled with surface examination and solution analysis is a effective tool to characterize and quantify the AC corrosion of mild steel in marine environments.

On the Rust Products Formed on Weathering and Carbon Steels Exposed to Chloride in Dry–Wet Cyclical Processes

The rust products formed on weathering and carbon steels exposed to dry-wet cyclical processes in different chloride-rich solutions are carefully examined by means of different techniques. Special emphasis is given to the methodology of analysis of the data using 300 K and 77 K Mossbauer spectrometry and X-ray diffraction. The rust that is loosely bound to the metal surface and that it is lost during the corrosion process, for both types of steel, was found to be composed of lepidocrocite, superparamagnetic goethite, hematite, and traces of akaganeite. On the other hand, the adherent rust, which is differentiated as scraped and hit according to the way it is obtained, from both steels was found to be composed of akaganeite, spinel phase, goethite exhibiting broad distribution of particle sizes and lepidocrocite. The relative abundances of rust components for both steels were very similar, suggesting similar corrosion processes. Mass loss measurements show that the corrosion rates increases with increasing the chloride concentration. The presence of large quantities of spinel phase and akaganeite are a consequence of a corrosion process under the influence of very high chloride concentrations. Our results are useful for assessing the behavior of weathering steels where the levels of chlorides are high or in contact with sea water.

Analytical model of corrosion-induced cracking of concrete considering the stiffness of reinforcement

The structural deterioration of concrete structures due to reinforcement corrosion is a major worldwide problem. Service life of the age-degraded concrete structures is governed by the protective action provided by the cover concrete against the susceptibility of the reinforcement to the corrosive environment. The corrosion of steel would result in the various corrosion products, which depending on the level of the oxidation may have much greater volume than the original iron that gets consumed by the process of corrosion. This volume expansion would be responsible for exerting the expansive radial pressure at the steel-concrete interface resulting in the development of hoop tensile stresses in the surrounding cover concrete. Once the maximum hoop tensile stress exceeds the tensile strength of the concrete, cracking of cover concrete would take place. The cracking begins at the steel-concrete interface and propagates outwards and eventually resulting in the through cracking of the cover concrete. The cover cracking would indicate the loss of the service life for the corrosion-affected structures. In the present paper, analytical models have been developed considering the residual strength of the cracked concrete and the stiffness provided by the combination of the reinforcement and expansive corrosion products. The problem is modeled as a boundary value problem and the governing equations are expressed in terms of the radial displacement. The analytical solutions are presented considering a simple 2-zone model for the cover concrete viz. cracked or uncracked. A sensitivity analysis has also been carried out to show the influence of the various parameters of the proposed models. The time to cover cracking is found to be function of initial material properties of the cover concrete and reinforcement plus corrosion products combine, type of rust products, rate of corrosion and the residual strength of the cover concrete. The calculated cracking times are correlated against the published experimental and analytical reference data.

Simulation of a long term atmospheric corrosion process on plain and weathering steels

Information on weathering steel behaviour and its rust products characteristics after decades of atmospheric exposure are scarce. On the other side, generally accepted laboratory tests for the assessment of its corrosion resistance have not been developed yet. Consequently, simulating corrosion in the laboratory during long periods of time is attractive for the interesting and complete information obtainable from them. In the present work, AISI-SAE 1008 and ASTM-588 B steel samples have been exposed for two years to a immersion-emersion CEBELCOR type test in the laboratory, simulating a moderate urban atmosphere. Two groups of six samples each were tested. After the first year, three samples of each batch were retired for analysis and the rest was kept until they reached two years of exposure. The half cell electrode potentials were measured daily. The rust was characterized by metallographic techniques, Mossbauer spectroscopy (MS), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). Comparison was done with field exposure experiments reported in the literature, and conclusions on the behaviour of tested samples were drawn looking for differences and similarities with samples and structures under actual atmospheric conditions.

Influence of reinforcement corrosion—in the compressive zone—on the behaviour of RC beams

In this paper, the influence of damage due to corrosion of reinforcement in the compressive zone of RC beams is analysed. In the damaged RC beams, the corrosion of reinforcement, as a consequence of an electrochemical process, produces an increase of diameter of bars due to rust products that gives rise to a microcracking of the concrete around the bars. In the compressive zone, the microcracking of concrete creates a loss of strength of concrete. A theoretical model to analyse the influence of reinforcement corrosion in the compressive zone of RC beams is described considering a modified law for concrete. The theoretical results are compared with the experimental data obtained from bending tests on undamaged and damaged RC beam models.

Products obtained by microbially-induced corrosion of steel in a marine environment: Role of green rust two

An unusual low-water corrosion of steel sheet piles has been systematically investigated in a channel harbour (Boulogne sur Mer, France). An analysis of the environment reveals that all sampling of dark rust taken at different heights above marine sediments and kept in anaerobic conditions present unusual concentrations of sulfate-reducing bacteria. The rust products have been characterized by Mossbauer spectroscopy and X-ray diffraction, comprising the ferrous—ferric sulfated compounds of formula 4Fe(OH)2 · 2FeOOH · FeSO4 ·nH2O, called green rust 2, mixed sometimes with magnetite and a small amount of ferrous sulfide.

Sharpening of autopsy tools.

This article describes basic tool-sharpening techniques in which grinding wheels, files, abrasive papers, stones, strops, and steels are used to repair and sharpen the edges of autopsy tools including chisels, knives, scissors, and shears. In general, files or grinding wheels are used to repair edges with gross defects such as burrs, nicks, or chips, or to restore the bevel of an edge, and then a stone is used to sharpen the edge; whereas abrasive paper, strops, or steels are used to remove rust or oxidation products and to touch up an already sharp edge immediately prior to use. Although pathologists may prefer to delegate the sharpening of tools to others or to buy new tools when old ones become dull, there may be occasions when knowledge of sharpening techniques is beneficial either to sharpen a tool or to ensure that proper sharpening techniques are used by others.

The role of Cl− ions in the oxidation of iron artifacts from chlorinated archeological environments

Mossbauer analysis of archeological iron artifacts allows to determine mainly the presence of the β ferric oxyhydroxide, akaganeite, in the rust products. This confirms the role of Cl− ions in the environment leading to difficult preservation in a museum.

A conversion electron mössbauer spectroscopic and gravimetric study of the hydrolytic oxidation of iron fluoride hydrate surface layers

The oxidation of FeF 2-4H 2O surface layers in an atmosphere saturated with water vapour was studied by means of Mössbauer spectroscopy as well as gravimetry. The major rust product is identified as β-FeOOH, and the reaction is shown to proceed as a front from the layer-atmosphere interface towards the substrate. The ratio of the initial amount of fluoride on the surface to the final amount of rust produced was found to be constant, with the fluoride present in 1 mole of FcF 2-4H 2O reacting further to yield more than 5 moles of oxyhydroxide. This constant and non-stoichiometric yield is explained in terms of an acid regeneration cycle.