Surface Of Steel Bar Research Articles

Investigation of effect of fineness dependent volume of fine aggregate on passive layer formation and corresponding corrosion of steel reinforced concrete using electrochemical approach

This paper aims to determine the effect of the fineness modulus of fine aggregate on the quality and development of passive film and its subsequent effect on the corrosion of reinforced concrete structures. The study uses both electrochemical laboratory controlled experimentation and finite element modelling approach. Corrosion is an electrochemical process that requires an electrolyte for the occurrence of a corrosion reaction. Therefore, it is necessary to calculate the effective corrosion rate with reference to the saturated area of the concrete only when there is corrosion of reinforced concrete structures. Theoretically and numerically, the saturated area depends on the capillary zone porosity, gel zone porosity and degree of saturation in the aggregate free volume of concrete, which is a heterogeneous material. It is thus important to understand the effect of aggregate fineness on the corrosion of steel rebars. Therefore, detailed investigations were conducted using a variety of fine aggregates and combinations thereof. The initiative for this research came from the observation that the interfacial transition zone (ITZ) around the steel bar in concrete does not contain coarse aggregate, but could be surrounded by mortar and not only paste. Hence, the fine aggregate volume may also influence the corrosion rate. Some fine aggregate, which is finer than coarse aggregate, could be present in the vicinity of the steel bar surface, depending on the fineness modulus, which may affect both the development of the passive layer and the corrosion rate. The previous research data in this area were found to be limited. Hence, these factors have been investigated in the present study. Both mortar and concrete prismatic specimens were cast, and the quality of passive layer development and the corrosion severity were compared between specimens to determine the effect of fine aggregate volume with respect to the respective fineness modulus values. The corrosion potential, current and rate values obtained through experimentation showed significant differences in their magnitudes with respect to the variation in the fineness modulus. A directly proportional relation was observed between the fineness modulus of fine aggregate and the corrosion of rebars. Therefore, in the light of the experimental results obtained in this study, a finite element based numerical model incorporating the effect of the fineness modulus of fine aggregate on corrosion of steel rebars in concrete has been developed and successfully verified in this study.

Electrochemical impedance study on steel corrosion in the simulated concrete system with a novel self-healing microcapsule

Based on microcapsule technology, a new type of self-healing system for concrete materials was created, which mainly focuses on the corrosion protection of steel bars. In this paper, the performance of the system is characterized by means of the electrochemical impedance spectroscopy (EIS) of steel bar immersed in a simulated concrete environment. The experimental results demonstrate strong inhibition of chloride-induced corrosion when microcapsules are added to the water solution with sodium chloride by different mass fractions. A novel equivalent circuit model, which takes into account the inductive effect arising from the generation of corrosion products on the steel bar surface, is proposed to explain the protection performance of the microcapsules against the corrosion of a steel rebar in a concrete.

Convenient routes to synthesize uncommon vaterite nanoparticles and the nanocomposites of alkyd resin/polyaniline/vaterite: The latter possessing superior anticorrosive performance on mild steel surfaces

Polyaniline (PANI)/Precipitated Calcium Carbonate (PCC) composite materials are prepared, for the first time, starting from naturally occurring calcite, and are well characterized. X-ray diffraction (XRD) studies provide information for the presence of unstable vaterite form of PCC in the composites, with an average crystallite size of 26nm, thus demonstrating the ability of PANI to stabilize, otherwise unstable, vaterite phase of CaCO3. Thermal analytical results (TGA and DSC) also provide information for the presence of only PANI and PCC, thus providing information for the purity of the composites. This method, therefore, provides a convenient route to prepare vaterite nanoparticles. Electron Microscopic (FE-SEM) images of the composites confirm that the voids of PANI chains are filled by the spherical nannoparticles of vaterite of diameter ∼ 24nm, to result in spheres of the composites with an average diameter of 3–4μm. FTIR spectra show that the PANI exists in its emaraldine form, weakly protonated when prepared at pH 5. Analysis of the FT-IR data for the four composites of PANI/vaterite gives the molar ratios of PANI:vaterite to be 1:4, 1:2, 1:1, 2:1, respectively. The PANI/PCC composites show electrical conductivity of ∼ 1.00×10−5 S cm−1, which is an impressive value to use these materials as anticorrosive coatings. AC impedance studies also give the conductivities of the PANI/PCC composites to be corresponding to a weakly electronically-conductive emeraldine form of PANI, with equal contributions from the ionic and electronic components, irrespective of the different amounts of vaterite or calcite present in the composites. The DC polarization test confirms equal transport numbers for ions and electrons in PANI samples. The above composites of PANI/vaterite, and a composite of 1:1 molar ratio of PANI/calcite, were mixed with alkyd resin and xylene, separately, to prepare anticorrosive coatings on mild steel (Mole percentages: 98.90% Fe, 0.26% C, 0.04% P, 0.05% S and 0.75% Mn) surfaces. All five composite coatings, with thickness ∼ 40μm, show dramatic decrease in corrosion current density, and a considerable increase in corrosion resistance, to result in several orders of magnitude lowering of the corrosion rate from that of bare mild steel surfaces and those coated with only alkyd resin. There are considerable positive shifts in the corrosion potential also, when each of the five coatings are applied, separately, on mild steel samples, which provide information for a significant overpotentials induced by these coatings on iron oxidation. All four Alkyd resin/PANI/vaterite coatings show higher anticorrosive performances (by factors of 2×104, 5×104, 1×105 and 1.67×104, respectively from that of bare mild steel) than that of the Alkyd resin/PANI/calcite coating (by a factor of 1.25×103 from the same). The improved pore-sealing by relatively smaller (26nm diameter) and spherical vaterite nanoparticles, when compared with a little larger (38nm) and somewhat elongated nanoparticles of calcite, is suggested to be responsible for better anticorrosive performance of the Alkyd resin/PANI/vaterite nanocomposites.

Understanding the Corrosion and Remedial Measures to Control the Deterioration of Reinforcement Steel Bars by Modification in Their Chemistry and Application of Surface Coatings

Corrosion of reinforcement bars embedded in structures near coastal areas is a serious problem and has been attributed to many premature distresses of structures. The passivity imparted by the alkalinity of the cement to reinforcement steel surface becomes ineffective when chloride concentration at the steel surface exceeds a critical threshold value. Under such a situation, the total loss of the steel thickness per unit area is negligibly small in comparison to penetration rate at certain susceptible part of the reinforcement bars. As a result of increase in stress intensity factor at the tip of localized pits formed on the surface of rebars, the tensile strength of the concrete structures which is mainly imparted by the steel reinforcement bars, is adversely affected and results in collapse of structures. Many techniques have been developed to control the corrosion problems associated with rebars. These include use of corrosion resistant alloys, corrosion inhibitors, cathodic protection and use of organic/metallic coatings on surface of steel bars. Amongst these techniques, the applications of surface coatings appear an effective and economical method to control corrosion of steel rebars. However, the efficacy and mechanism of their protective action are still matter of controversy and subject matter of studies all over the world. The present work is in continuation of our earlier studies published in different scientific journals where the above aspects had been addressed. This paper incorporates experimental results and literature review in understanding the corrosion and remedial measures to control the deterioration of reinforcement steel bars by modification in their chemistry and application of surface coatings. A brief historical background is given on development of reinforcement concrete structures. Various types of reinforcement bars used in construction industries and their merits and demerits are described. It has been established by the experimental proofs that the current scenario of protecting steel rebars used in chloride contaminated concrete, is not at all satisfactory. Amongst the protective coatings, metallic coated rebars appear to be more effective than organic based coatings. Causes and mechanism of deterioration of coated and bare steel rebars are discussed by providing experimental evidences.

Electroplating of Nickel on Nickel Titanate Modified Mild Steel Surface

Nickel is a good electrocatalytic metal and nickel electrodes find many applications in different electrochemical fields. The nickel plated electrodes were prepared by electro-deposition technique on mild steel surface modified with in-situ deposition of nickel titanate. The SEM images shows that the nickel plating on nickel titanate modified mild steel shows better adherence than the nickel plating on bare mild steel surfaces. The extent of polarization of the nickel plating on mild steel with nickel titanate was lower than that of nickel plating on mild steel. The incorporation of nickel titanate on mild steel surface before nickel plating enhances physical, chemical and electrochemical properties of the plating film.

Analysis of Steel Bar Surface Defects Based on Machine Vision

In order to guarantee the steel bar quality, we describe the category of steel bar surface defects in details. Generally, there are about two main categories of steel bar surface defects which include linear and area-like defects. Secondly, the characteristics of the steel bar surface image are analyzed at large. Both of them support a foundation for the future inspection of steel bar surface quality.

A lower envelope Weber contrast detection algorithm for steel bar surface pit defects

A lower envelope Weber contrast (LEWC) recognition algorithm is proposed to detect steel bar surface pit defects. Some present algorithms could detect these defects but they are limited by the size of pits. This kind of defect has uniform background intensity in column pixels of steel bar surface images while it is not the case in row pixels. The lower envelope of column pixels is used to eliminate the effect of high gray level peak value points, and Weber contrast is employed to make that all areas in one image have the same threshold to detect pit defects. Experimental results show that the proposed LEWC algorithm has a high detection accuracy rate which exceeds 98% for the pit defects with different sizes.

Design of Automatic Detection Device for Steel Bar Surface Defects

To inspect the surface quality of steel bar, we designed an automatic system including linear camera and laser. Through the comparison among kinds of cameras, we select linear CCD to our system. The laser is also chosen by us with its high luminance and performance. Through a series of computation, we select the appropriate camera lens to our device. At last, we draw the whole detection system. This device has been used well and provides a good foundation for prospective image processing.

State‐of‐the‐Knowledge on Coating Systems for Hot Stamped Parts

AbstractIn the present contribution, recent developments of coatings for hot stamped steels are reviewed. The use of bare steel in the initial hot stamping technology is discussed, including the application of lubricant oils which are used as oxidation inhibitors on bare steel surfaces. The aluminized coatings are introduced, focusing on the microstructure evolution of aluminized coatings during the hot stamping process. An analysis of the cracking of the coating, caused by the formation of brittle Fe–Al intermetallic phases and their high temperature deformation, is presented. The development of a ductile aluminide coating formed during the diffusion treatment of an aluminized coating is discussed. This aluminide coating can endure both high temperature oxidation and severe plastic deformation. The recently developed galvanized and galvannealed coatings are also reviewed and the influence of the gas atmosphere during the heating cycle on the coating stability is emphasized. The solutions which have been proposed to avoid liquid Zn‐induced embrittlement are analyzed. The use of Zn–Ni alloy coating, which is characterized by a higher melting temperature, is reviewed. The behavior of sol–gel hybrid coatings on hot stamped steels is discussed. The possible use of the recently developed Al–Zn alloy coatings, dual layer Zn–Al and Zn–Al–Mg coatings is also introduced. The application of Zn–Al–Mg post‐process galvanizing is also discussed. In each case, all available information related to the weldability, paintability, and corrosion resistance of the coating systems is also reported. Finally, the advantages and technical challenges associated with each type of coating are reviewed.

A local annular contrast based real-time inspection algorithm for steel bar surface defects

A new inspection algorithm based on local annular contrast (LAC) for steel bar surface defects is presented. Because of little fluctuation of gray value inside the defects, traditional gradient detection methods could not find the defects accurately and often mistake the boundary of the bright region in center for defects. The LAC-based algorithm doesn’t have this disadvantage. Defects in images can be found due to their large contrast with local annular background (LAB). After average filter to steel bar surface image, the noise could be smoothed to a great extent but the contrast between defects and LAB changes very little. Then the LAC-based algorithm is applied to inspect defects. Experimental results show that the proposed algorithm needs only 13ms to inspect one steel bar surface image and its detection accuracy exceeds 95%.

Effect of bicarbonate on corrosion of carbon steel in CO 2 saturated brines

The effect of bicarbonate concentration (HCO 3 −) on bare steel surface corrosion was investigated experimentally in ambient CO 2-saturated solutions. In the presence of CO 2, pH was adjusted by adding NaHCO 3 solution or powder. Corrosion rate decreased with pH increasing at the range of pH 4–5, was little changed at pH 5–6 and interestingly increased at pH 6–8. Thermodynamic calculations of CO 2 aqueous speciation showed that only bicarbonate concentration increased as pH increased from 4 to 8 while the other corrosion-active species including proton and carbonic acid either decreased or changed little, respectively. Thus we have demonstrated that bicarbonate is an active corrosion species and is important to corrosion at pH 6–8. Our earlier mechanistic corrosion model ( Han et al., 2011a) was modified to incorporate bicarbonate-induced corrosion and demonstrated good agreement with experimental observations.

Investigation of volumetric effect of coarse aggregate on corroding steel reinforcement at the interfacial transition zone of concrete

Corrosion is an electrochemical process which requires electrolyte for the occurrence of corrosion reaction. Therefore it is necessary to calculate the effective corrosion rate with reference to the saturated area of concrete only when it comes to corrosion of steel reinforcement embedded in concrete. Theoretically and numerically the saturated area depends on the capillary zone porosity, gel zone porosity and their respective degree of saturation in the aggregate free volume of concrete which is a heterogeneous material in nature. This makes it important to deeply understand the effect of aggregate on corrosion in concrete. Investigation was carried out to find the effect of coarse aggregate volume on the corrosion rate and potential of reinforcement steel in concrete. The initiative for this research came from the observation that the interfacial transition zone around the steel bar in concrete is surrounded primarily by paste only and hence the coarse aggregate volume should not influence the corrosion rate principally. Also there are chances that some fine aggregate could be present in the vicinity of steel bar surface being finer than coarse aggregate which may affect the corrosion rate. The previous research data in this field was found to be limited and has a difference of opinion. Therefore, these factors have been investigated in this research. Prismatic concrete and mortar specimens were cast and their corrosion potential values were compared with each other to find the effect of the volume of coarse aggregate on corrosion. The experiment results showed that the effect of the volume of coarse aggregate on corrosion potential is not significant since the area around the steel bar especially in the case of deformed steel is mostly surrounded by paste only. The corrosion potential values obtained in the case of mortar and concrete specimens showed same averaged magnitude. This fact was further strengthened by measuring the corrosion mass loss and resulting corrosion rate in the two cases. Furthermore, in the light of experiment results obtained in this research, the numerical FEM model DuCOM developed by our research group at the University of Tokyo, Japan incorporating the effect of aggregate on corrosion rate and potential of corroding steel in concrete undertaken in the past has been successfully enhanced and verified in this research.

Investigation of the Galvanic Mechanism for Localized Carbon Dioxide Corrosion Propagation Using the Artificial Pit Technique

Abstract Localized carbon dioxide (CO2) corrosion is the most dangerous type of internal corrosion to mild steel pipelines in the oil and gas industry since the penetration rate of localized corrosion can be one or more magnitudes higher than that of uniform corrosion. In this study, the focus is on propagation of localized CO2 corrosion on mild steel that occurs by a galvanic mechanism. A galvanic cell is established by the coupling of two distinct areas in a conductive CO2 solution: a bare steel surface and an iron carbonate (FeCO3) layer-covered steel surface. It was found that localized CO2 corrosion propagates when a stable difference in corrosion potential is established between the anode (bare steel surface) and the cathode (FeCO3-covered surface). Stable propagation will occur only when the conditions are in the “gray zone,” i.e., close to saturation with respect to FeCO3, when no significant FeCO3 dissolution nor precipitation is expected. Practically, this corresponds to when FeCO3 supersaturati...

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.

Influence of connectivity of concrete pores and associated diffusion of oxygen on corrosion of steel under high humidity

This paper investigates the limitation of oxygen diffusion under high relative humidity condition in comparison to submerged, alternate wetting–drying and air dry conditions and its influence on the corrosion rate of steel by blocking the pores of concrete with moisture and reducing the connectivity required for transfer of gaseous oxygen from the environment to the steel bar surface. This was achieved through multi-variable experimentation for which the previous research is limited and has difference of opinion. It is concluded from the observed trend in the case of high relative humidity and submerged condition that once concrete specimens are subjected to these conditions; there is a reactivation of curing and hydration process which leads to low porosity and connectivity of concrete pores making it harder for oxygen to diffuse. The findings are quantified in terms of practical field variables such as cover depth and water/cement ratio. This deep experimental investigation involving a variety of material and environmental variables under a wide spectrum of boundary conditions will help in better understanding and will open several significant future prospects of research in the modeling of corrosion under limited oxygen availability.

Effect of W/C ratio and cover thickness on polarization characteristics of embedded steel in mortar

The effects of cover thickness and W/C (water-to-cement) ratio on polarization properties of embedded steel bar were investigated with electrochemical methods. Corrosion potentials shift to the noble direction with increasing the cover thickness. In addition, when the cover thickness increasingly becomes thinner and thinner, effect of the W/C ratio on variation of corrosion potential increases as well. Impedance value at 100 kHz indicating the resistance of cover thickness increases with the decrement of W/C ratio as well as the increment of cover thickness. However, in the case of W/C ratio at 0.6, impedance at 10 mHz shows the relatively larger value than that at W/C ratio of 0.4 or 0.5 in the range of cover thickness from 4 to 8 cm, which is probably expected that oxide film built up on the surface of steel bar due to strong alkali environment by hydration reaction with increasing W/C ratio is performed as the resistance polarization. It is also observed that liquid junction potential tends to increase with decreasing W/C ratio.

The effect of plasma‐polymerised silicon hydride‐rich polyhydrogenmethylsiloxane on the adhesion of silicone elastomers

AbstractBACKGROUND: Silicone elastomers have outstanding material properties including good thermal stability, low electrical conductivity, biocompatibility and resilient physical and chemical properties. These elastomers, however, exhibit relatively poor adhesion to stainless steel, and the use of a nanometre thick plasma‐polymerised primer layer as a means of enhancing this adhesion was investigated in this study. The primer coatings studied consisted of polyhydrogenmethylsiloxane (PHMS), tetraethyl orthosilicate (TEOS) and mixtures of these two liquid precursors.RESULTS: The plasma‐polymerised primer coatings were deposited onto stainless steel substrates using a PlasmaStream™ atmospheric pressure plasma jet system. Deposited coatings were examined using ellipsometry, contact angle measurements, optical profilometry, Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy and scanning electron microscopy. The adhesion of silicone elastomers bonded to the primed and bare stainless steel surfaces was assessed using 45° adhesion strength measurements. Elastomer adhesion was correlated with surface energy, thickness and roughness.CONCLUSION: An up to 15‐fold increase in adhesive fracture energy was observed for silicone elastomers bonded to the primed versus untreated stainless steel. The highest adhesion was observed for a coating deposited from a PHMS‐to‐TEOS precursor molar ratio of 3 to 1. Copyright © 2009 Society of Chemical Industry

Analysis of steel/concrete interfacial shear stress by means of pull out test

The excellent mechanical performance of epoxy resins has encouraged their wide-spread application in civil engineering. This paper deals with the prediction of the interfacial shear strength between the steel bar surface and concrete surface of steel rods bonded into concrete. The pull out test is used in order to determine the ultimate force and the shear stress of steel–concrete specimens. The relationship between the ultimate force, the diameter and the length embedded into the concrete are investigated by experimental test. After discussing some theoretical models, a theoretical model is also proposed in this work in order to estimate the shear distribution and the critical shear stress at the instance that the first cracks appear and of the ultimate failure of steel/concrete structure. A comparison between the test and the theoretical results is provided.

Comparison of Two Accelerated Corrosion Techniques for Concrete Structures

The galvanostatic method of inducing corrosion is commonly employed in laboratory tests to study the influence of reinforcing bar corrosion on the response of the reinforced concrete beams. However, the surface characteristics of the corroded steel bar are found to be different when the corrosion is induced by galvanostatic method or by natural environment. This study proposes an alternative method of inducing corrosion using an artificial climate environment and seeks to verify if it can be adopted as an accelerated technique for the durability test in place of the galvanostatic method. Two groups of reinforced concrete beams were degraded as a result of the corrosion of steel bars. One group of beams was subjected to the galvanostatic method, while the other group was corroded using the artificial climate environment. Comparative studies on the corroded characteristics of steel bar surface, the mechanical behavior of the corroded bar, and the load-bearing capacity were conducted. The comparisons between the two groups of beams were based on the identical width of corrosion cracking. The comparison revealed significant differences in the two methods. The steel bar in concrete can be corroded using the galvanostatic method, but its electrochemical corrosion process is different from the corrosion process under the artificial climate and natural environment. The differences lead to different corrosion distribution on the surface of the steel bar. The corrosion process and corrosion characteristics of the steel bar under artificial climate environment were similar to that of corrosion under natural environment, suggesting that the artificial climate environment is more representative than the galvanostatic method as an accelerated laboratory test method.

A study on tribological behaviour of transfer films of PTFE/bronze composites

Transfer films of PTFE/bronze composites with 5–30% volume content of bronze were prepared using a RFT friction and wear tester on surface of AISI-1045 steel bar by different sliding time (5–60 min). Tribological properties of these transfer films were studied using a DFPM reciprocating tribometer in a point contacting configuration under normal loads of 0.5, 1.0, 2.0 and 3.0 N. Thickness and surface morphology of the transfer films were investigated. It was found thickness of the transfer films slightly increased along with the increase of bronze content of corresponding composites. Increased sliding time of transfer film preparation is helpful to form transfer film with better ductibility and continuity, but sliding time almost has no effect on tribological properties of the transfer film. Higher bronze content in the composite improved tribological properties of the corresponding transfer film, i.e., reduced friction coefficient and prolonged wear life. All these transfer films are sensitive to load change. Their wear life becomes shorter along with the increase of load. SEM image of the worn surface show fatigue wear and adhesion wear have happened on the transfer film during the friction process. The author believe bronze in the transfer film effectively partaked in shear force applied on the transfer film and its good ductibility helped to improve tribological properties of the transfer films.