Mass Loss Of Steel Research Articles

Influence of corrosion crack patterns on the rate of crack widening of RC beams

Corrosion crack widths are often used by structural engineers in the field to predict level of steel corrosion as well as residual load-bearing capacities of corroding RC structures. This paper presents further work on this matter but with focus on corrosion crack patterns and how they affect rate of crack widening. It is based on results from a research where 17 quasi-full-scale (153 × 254 × 3000 mm) RC beams were corroded under various levels of sustained loads. The rate of widening of corrosion crack widths was found to be very much dependent on crack patterns. Deformation of cover concrete under each crack pattern was discussed. It was found that at maximum crack widths below 0.6 mm, the majority of beams exhibited nearly similar crack patterns as well as rate of widening of corrosion cracks. A mass loss of steel of 1% corresponded to a maximum crack width between 0.14 and 0.22 mm. At large crack widths (>0.6 mm), various beams exhibited very different rates of crack widening. It was shown that at crack widths above 0.6 mm, to be conservative an increase in mass loss of steel of 1% corresponded to corrosion crack widening of 0.02 mm.

Interaction between corrosion crack width and steel loss in RC beams corroded under load

This paper presents results and discussions on an experimental study conducted to relate the rate of widening of corrosion cracks with the pattern of corrosion cracks as well as the level of steel corrosion for RC beams (153 × 254 × 3000 mm) that were corroded whilst subjected to varying levels of sustained loads. Steel corrosion was limited to the tensile reinforcement and to a length of 700 mm at the centre of the beams. The rate of widening of corrosion cracks as well as strains on uncracked faces of RC beams was constantly monitored during the corrosion process, along the corrosion region and along other potential cracking faces of beams using a demec gauge. The distribution of the gravimetric mass loss of steel along the corrosion region was measured at the end of the corrosion process. The results obtained showed that: the rate of widening of each corrosion crack is dependent on the overall pattern of the cracks whilst the rate of corrosion is independent of the pattern of corrosion cracks. A mass loss of steel of 1% was found to induce a corrosion crack width of about 0.04 mm.

Variation of steel loss and its effect on the ultimate flexural capacity of RC beams corroded and repaired under load

Abstract This paper presents results of an investigation on the variation of mass loss of deformed tensile steel bars in RC beams (153 × 254 × 3000 mm) that were corroded whilst under a sustained load using an impressed current, constant wetting cycles with 5% NaCl solution and two different drying cycles. Following the corrosion test, selected beams were patch repaired whilst under a sustained load, but eventually all beams were tested to failure. The results indicated that the highest level of corrosion occurred where there were longer drying cycles, and that the level of sustained load had little effect on the rate of corrosion. Maximum mass loss of steel was found to occur at the centre of the corrosion region. The ultimate flexural capacity of beams was found to be best related to the maximum gravimetric mass loss compared to the average mass loss of steel. A maximum mass loss of steel of 1% was found to reduce the flexural capacity of beams by 0.7%.

Post-repair performance of eccentrically loaded RC columns wrapped with CFRP composites

This paper presents the results of a research program for examining the post-repair performance of eccentrically loaded corrosion-damaged reinforced concrete (RC) columns wrapped with carbon fiber reinforced polymer (CFRP) composites. The specimens, except a control undamaged group, were initially exposed to accelerated corrosion for 30 days using an impressed current technique. Following the initial corrosion, the damaged specimens were either repaired with full or partial CFRP wrapping systems or kept unrepaired. A group from the damaged specimens were further exposed to 60 days of corrosion exposure. All specimens were tested to failure under various eccentric loading with a nominal eccentricity-to-section height ratio (e/h) in the range of 0.3–0.86. Test results showed that full CFRP wrapping system effectively reduced the post-repair corrosion rate relative to that of the unwrapped specimens whereas partial CFRP wrapping had almost no effect on the steel mass loss. The strengths of the damaged specimens fully wrapped with CFRP were higher than those of the control specimens at the end of the post-repair corrosion phase. The strengths of the damaged partially wrapped specimens were higher than those of the control at nominal e/h values ⩽0.43. At higher e/h values, the strengths of the partially wrapped specimens were lower than those of the control but still higher than those of the damaged unrepaired specimens. An analytical model that accounts for the confinement effect of the CFRP and the change in geometry under eccentric loading was employed to predict the columns’ strength. The model’s predictions were validated against test results.

Influence of transverse crack width on reinforcement corrosion initiation and propagation in mortar beams

This paper discusses the relationship between crack widths, chloride diffusivity, and corrosion rate of cracked mortar beams. Flexural loads are introduced to generate crack widths ranging from 29 to 390 µm. The specimens were subjected to accelerated corrosion by immersion in a 5% NaCl solution and a constant voltage of 12 V. In addition, salt ponding tests were conducted to determine the chloride ion transport properties. The results showed that as the crack width increased, the effective diffusion coefficient (corrosion initiation) and mass loss of steel reinforcing bars due to the accelerated corrosion (corrosion propagation) also increased. For crack widths less than about 135 µm, the effect of crack width on the effective diffusion coefficient and mass loss of steel reinforcing bars embedded in mortar specimens was found to be marginal when compared with the virgin specimens. Therefore, it was concluded that the effect of crack width on the corrosion initiation and propagation period was more pronounced when the crack width is greater than about 135 µm. Moreover, a significant amount of self-healing was observed for the cracks that have widths below 50 µm when subjected to the NaCl solution exposure.

Behavior of corrosion-damaged RC columns wrapped with FRP under combined flexural and axial loading

Abstract This paper presents the results of a research program aimed at investigating the effectiveness of carbon fiber-reinforced polymers (CFRP) to upgrade corrosion-damaged eccentrically loaded reinforced concrete (RC) columns. A total of 16 square RC columns with end corbels were constructed. Test specimen had an overall length of 1200 mm whereas each end corbel had a cross section of 250 × 250 mm and a length of 350 mm. The specimen in the test region was 125 × 125 mm having longitudinal steel ratio of 1.9%. The damaged specimens were exposed to 30 days of accelerated corrosion that corresponded to a steel mass loss of about 4.25%. The main test parameters were the CFRP repair scheme (no wrapping, full-wrapping, and partial-wrapping) and the eccentricity-to-section height ( e / h ) ratio (0.3, 0.43, 0.57, and 0.86). The strength of the damaged columns fully wrapped with CFRP was up to 40% higher than that of the control undamaged columns. The strength gain was inversely proportional to the eccentricity ratio. Partial CFRP-wrapping was 8% less effective than full CFRP-wrapping at nominal e / h of 0.3. At higher e / h values, the confinement level had a negligible effect on the columns’ strength. An analytical model was then proposed to predict the columns’ strength under eccentric loading. A comparative analysis between predicted and experimental results demonstrated the model’s accuracy and reliability.

Consequences of steel corrosion on the ductility properties of reinforcement bar

In all concrete constructions besides the common strength problems, in presence or not of seismic activity, serious problems from environmental attack may be presented which significantly decrease their durability and service lifetime. The most common case of construction deterioration is the corrosion of steel reinforcement. The initiation mechanisms leading to steel depassivation, such as concrete carbonation and chloride penetration, have been thoroughly studied and modeled in the past. However, for the corrosion propagation period still there are no acceptable models to simulate the corrosion rate and further to estimate precisely the time when the corrosion progress signals the end of the structure service life. In the present work, the main corrosion initiation mechanisms are shortly presented. Further, the propagation period and the main consequences on mechanical properties of steel and concrete are analyzed. The experimental results show that with increasing duration of exposure to a corrosive environment, the steel mass loss increases appreciably. This leads to a significant increase of the applied stress. In addition, a significant reduction of the tensile ductility of the material was observed. For laboratory salt spray exposure periods, some of the tensile properties of steel bars drop to values lying below the limits, which are set in the existing standards for using steels in reinforced concrete members. The experimental results from the accelerated corrosion tests on bare steel bars are in a good qualitative agreement with results from steel bars embedded in aged concrete.

Impact of Corrosion on Mass Loss, Fatigue and Hardness of BSt500s Steel

The impact of corrosion on the properties of steel reinforcement in concrete structures was examined. An experimental investigation was carried out in order to gain better insight of the effect of corrosion on the mass loss, fatigue and hardness, of BSt500s 12 and 8 mm diameter steel bars that were artificially corroded in a Sodium Chloride environment for different corrosion levels. The fatigue limit of the 12 mm steel was reduced by 20–40% and the mass loss was 1.5–2.9% for 15 and 30 days corrosion level, while the mass loss of the 8 mm steel was 1.2–32% for 10–90 days corrosion. The hardness of the 8 mm steel was reduced by 25–35% and 2–10% in the outer and inner layers of the specimens for 30 and 60 days corrosion respectively. Corrosion created considerable reduction in the fatigue strength and life of the steel bars due to drastic drop in the energy density, formation of pitting and notches along with destruction of the hardest outer layer of martensite.

A model for prediction of time from corrosion initiation to corrosion cracking

Abstract Prediction of time to corrosion cracking is a key element in evaluating the service life of corroded reinforced concrete (RC) structures. This paper presents a mathematical model that predicts the time from corrosion initiation to corrosion cracking. In the present model a relationship between the steel mass loss and the internal radial pressure caused by the expansion of corrosion products is developed. The concrete around a corroding steel reinforcing bar is modeled as a thick-walled cylinder with a wall thickness equal to the thinnest concrete cover. The concrete ring is assumed to crack when the tensile stresses in the circumferential direction at every part of the ring have reached the tensile strength of concrete. The internal radial pressure at cracking is then determined and related to the steel mass loss. Faraday’s law is then utilized to predict the time from corrosion initiation to corrosion cracking. The model accounts for the time required for corrosion products to fill a porous zone before they start inducing expansive pressure on the concrete surrounding the steel reinforcing bar. The accuracy of the model is demonstrated by comparing the model’s predictions with experimental data published in the literature.

Performance Evaluation of Carbon Fiber-Reinforced Polymer-Repaired Beams Under Corrosive Environmental Conditions

This paper presents results of an experimental study designed to evaluate the performance of reinforced concrete beams repaired with carbon fiber reinforced polymer (CFRP) sheets under corrosive environmental conditions. A total of 16 beams, 152 x 254 x 3200 mm each, were tested. One beam was used as a control while 15 beams were initially corroded electrochemically for 50 days that corresponded to approximately 9% steel mass loss. Following the initial corrosion, one beam was tested to failure while 14 beams were repaired with a flexural CFRP sheet along with a continuous wrapping or an intermittent wrapping. Following repair, two repaired beams were tested to failure while 12 beams were subjected to additional corrosion exposure for up to 310 days that corresponded to a maximum steel mass loss of approximately 34%. Six beams were exposed to additional corrosion under a sustained load to simulate a service condition. Test results showed that the beams of intermittent wrapping had a higher steel mass loss rate and thus a lower strength than the beams of continuous wrapping. The presence of the sustained load and associated flexural cracks during the post-repair corrosion exposure slightly increased the steel mass loss rate, which further reduced the beam yield load but it had no noticeable effect on the beam ultimate strength.

Effect of Fiber-Reinforced Polymer Wraps on Corrosion Activity and Concrete Cracking in Chloride-Contaminated Concrete Cylinders

This paper presents the results of an experimental study designed to investigate the effect of fiber-reinforced polymer (FRP) wraps on corrosion activity and concrete cracking in chloride-contaminated concrete cylinders. Thirty-five concrete cylinders, each having 102 mm diameter and 204 mm height, concentrically reinforced with one steel reinforcing bar, were subjected to accelerated corrosion exposure for 80 days. Test parameters included level of applied potential, presence of FRP wraps, and bar diameter. The corresponding current and concrete expansion were continuously monitored throughout the corrosion exposure. At the end of the test, the steel bars were extracted, cleaned of rust, and weighed to determine the actual steel mass loss. The results showed that, for the same applied fixed potential, FRP wraps effectively reduced the corresponding current, the concrete expansion, and the steel mass loss. For the same applied potential, the current density increased as the bar diameter decreased. For the same corrosion depth, the circumferential expansion of the cylinder caused by corrosion decreased as the concrete cover-to-bar diameter ratio (c/d) increased.

Electrode Erosion of a High Energy Impulse Spark Gap Switch

Based on the principle of thermal conduction, three metal alloys (stainless steel, copper-tungsten and graphite) were chosen as the material of the high impulse current discharging switch. Experimental results indicate that the mass loss and surface erosion morphology of the electrode are related with the electrode material (conductivity σ, melting point Tm, density ρ and thermal capacity c) and the impulse transferred charge (or energy) per impulse for the same total impulse transferred charge. The experimental results indicate that the mass loss of stainless steel, copper-tungsten and graphite are 380.10 μg/C, 118.10 μg/C and 81.90 μg/C respectively under the condition of a total impulse transferred charge of 525 C and a transferred charge per impulse of 10.5 C. Under the same impulse transferred charge, the mass loss of copper-tungsten (118.10 μg/C) with the transferred charge per impulse at 10.5 C is far larger than the mass loss (38.61 μg/C) at a 1.48 C transferred charge per impulse. The electrode erosion mechanism under high energy impulse arcs is analyzed briefly and it is suggested that by selecting high conductive metal or metal alloy as the electrode material of a high energy impulse spark gap switch and setting high erosion resistance material at the top of the electrode, the mass loss of the electrode can be reduced and the life of the switch prolonged.

Carbon-Fiber-Reinforced Polymer Repair to Extend Service Life of Corroded Reinforced Concrete Beams

This paper presents the results of an experimental study designed to investigate the viability of using externally bonded carbon-fiber-reinforced polymer (CFRP) laminates to extend the service life of corroded reinforced concrete (RC) beams. A total of 14 beams, 152×254×3,200 mm each, were tested. Three beams were not corroded; two of them were strengthened by CFRP laminates, while one specimen was kept as a virgin. The remaining 11 beams were subjected to different levels of corrosion damage up to a 31% steel mass loss using an impressed current technique. Six of the corroded beams were repaired with CFRP laminates, whereas the remaining five beams were not repaired. Eventually, all specimens were tested to failure under four-point bending. Corrosion of the steel reinforcement significantly reduced the load-carrying capacity of RC beams. At all levels of corrosion damage, CFRP repair increased the ultimate strengths of the corroded beams to levels higher than the strength of the virgin beam but significa...

Corrosion-enhancing potential of Shewanella putrefaciens isolated from industrial cooling waters

Microbially influenced corrosion (MIC) is catalysed by a series of metabolic activities of selected micro-organisms, notably by oxidation of cathodic hydrogen by hydrogenase, by hydrogen sulphide and by reduction of ferric iron. The sulphate-reducing bacteria are considered to be the most common catalyst of MIC, whereas the role of other bacteria has been neglected. This study examined the corrosive potential of the facultative sulphide producer, Shewanella putrefaciens, isolated from an industrial cooling water system. Shewanella putrefaciens was shown to reduce ferric iron and sulphite under anaerobic conditions and with ferric iron being the preferred electron acceptor. The isolate could utilize cathodic hydrogen as an energy source, especially when using sulphite as a terminal electron acceptor. In pure culture corrosion experiments, the highest mass loss of mild steel was observed in the presence of sulphite as sole electron acceptor, although mass loss was also detected where ferric iron was the sole electron acceptor. Our data indicate that S. putefaciens plays a role in MIC as it was able to catalyse a variety of corrosion-promoting reactions and to corrode mild steel under pure culture conditions.