Impressed Current Method Research Articles

Corrosion effects on flexural behaviour of EPS sandwich concrete panels: a study using acoustic emission technique

The experimental research utilized expanded polystyrene (EPS) panels sized at 1300 × 600 × 130 mm (length × width × thickness) and induced with corrosion via an impressed current method. Varied extents of corrosion were applied for 120, 240, 360, and 480 h, resulting in mass loss percentages of 6.67%, 8.41%, 10.76%, and 18.13% of reinforcement in different panels. The flexural testing along with acoustic emission (AE) monitoring were performed for evaluation of EPS panels. Results obtained defend the correlation of AE energy with the load energy in the EPS panels. The AE parameters of rise angle and average frequency assist in distinguishing between tensile and shear crack types. The energy released during tensile crack formation in EPS panels is minimal compared to that during shear crack formation. These findings are a basis for further AE investigations into EPS panels and developing AE sensor-based methods for identifying corrosion-induced degradation in EPS panels within structures.

Experimental and numerical investigation on seismic performance of corroded RC columns of low-strength concrete

A huge number of reinforced concrete structures designed without aseismic consideration exist at the risk of both reinforcement corrosion and earthquake. They were generally made of low-strength concrete and loaded with a relatively large compression ratio. A total of 11 RC columns of low-strength concrete with different corrosion degrees were obtained by the impressed current method, and low-cycle repeated loading tests were carried out on the columns with axial compression ratios ranging from 0.25 to 0.75. The seismic performance of corroded RC columns of low-strength concrete was analyzed through a discussion of the impact of reinforcement corrosion on failure modes, hysteretic behavior, skeleton curve, and energy dissipation capacity. For a more comprehensive understanding of the seismic performance of corroded RC columns, a numerical model based on the multi-spring model was developed by introducing a restoring model of corroded rebars. The numerical simulation results showed a good agreement with experimental results. With the verified numerical model, the influence of concrete strength, reinforcement ratio, and axial compression ratio on the impact of reinforcement corrosion on the seismic performance of RC columns was further investigated. It is found that the seismic performance of RC columns decreases rapidly with the increase of axial compression ratio and corrosion degree. As the axial compression ratio increases, the impact of reinforcement corrosion on the seismic performance is gradually weakened owing to the decreased contribution of longitudinal rebars to the load-carrying capacity. For similar reasons, the impact of reinforcement corrosion is more obvious in RC columns of low-strength concrete with a larger reinforcement ratio.

Evaluation of corrosion resistance of precast reinforced concrete subjected to early-age ambient pressure carbonation curing by accelerated impressed current method

In this paper, early-age ambient pressure carbonation curing was successfully developed to lower the corrosion risk by avoiding deep CO2 penetration and preserving high pH around the steel surface. The effect of ambient pressure carbonation on the resistance of chloride-induced rebar corrosion was evaluated by applying an accelerated impressed current (IC) as a trigger. Due to improved physical properties, carbonation-cured concrete had a lowered current reading, a reduced rebar mass loss, a lessened total or free chloride content, and a decreased chloride diffusivity. Its time-to-corrosion-initiation and corrosion-propagation stages were also extended, which could strengthen the structural integrity and extend the residual service life of reinforced concrete components after corrosion initiation. Ambient pressure carbonation-cured concrete is corrosion resistant while still having the capacity to sequestrate carbon dioxide, which could contribute to the sustainability and circular carbon economy.

Bond behavior between corroded steel bar and concrete under sustained load

The degradation of bond behavior between corroded steel bars and concrete under sustained load is among the main issue for the durability of structures. In this study, the impressed current method was used to achieve target corrosion levels of tensile steel bar (0%, 1%, 3%, and 5%), while specimens bearing the sustained load (0%, 25%, 45%, and 65% ultimate load). The sustained load lasted for 60 days, during which the instantaneous slip and time-dependent slip were recorded. Finally, the bond strength of all kinds of specimens was measured by the flexural-bond test. The test results show that corrosion and load significantly affect the slip and bond strength between steel bar and concrete. Slight corrosion (less than 1%) leads to higher bond strength, up to 1.22 times that of the control group, while severe corrosion (more than 2.42%) leads to lower. Additionally, the strength reduction caused by the coupling of load and corrosion is more obvious than the single, by up to 45.66%. In addition, based on the test results, the time-dependent slip and bond strength prediction model were proposed, which can be used for predicting the service life of structures in the erosive environment.

Corrosion control of reinforced concrete structures in construction industry: A review

Corrosion of steel reinforcement is one of the main deterioration phenomena which affect the durability of reinforced concrete structures. Together with the structural damages, corrosion will also increase the cost associated with it. Therefore, protection of reinforcing steel in concrete structures from corrosion is an inevitable need. Various protection techniques are in practice to mitigate corrosion of reinforcing steel in the concrete structure such as use of patch repairing, protective coating, impressed current method, and sacrificial anodes. Among these, electrochemical protection technique using sacrificial anodes can be suggested as a very effective tool for corrosion mitigation. Sacrificial anode cathodic protection system is a less popular corrosion control technique because of lack of awareness about the benefits of this method and the wide usage of other corrosion control practices. This paper provides a critical review on the common techniques in construction sites used for corrosion control of reinforced concrete structures. An overview of the benefits of sacrificial anode cathodic protection system, its working and installation is also provided in this paper.

Parameters determining the quality of corrosion damage, induced by impressed current density technique, on steel reinforcement

PurposeIn the present study, an effort has been made to estimate the effect of significant parameters on the vulnerability of steel reinforcement to corrosion, using both impressed current density technique and Tafel extrapolation method.Design/methodology/approachFive sets of tests were performed. Corrosion vulnerability of various diameters, temperature and pH effect on the corrosion process, potential corrosion tendency after a precorrosion period and declination from the theoretical damage prediction model are some of the parameters examinedFindingsThe results of the tests provide useful information on the main parameters, determining the quality of the corrosion damage.Originality/valueThe originality of the present study is the fact that an effort has been made to estimate the effect of significant parameters on the vulnerability of steel reinforcement to corrosion, using both impressed current density technique and Tafel extrapolation method. Interesting conclusions emerged.

Effect of fly ash and corrosion on bond behavior in reinforced concrete

AbstractReinforcing steel bar can exert its strength and ductility by bonding to concrete. However, corrosion of steel bars reduces the bonding effect. This study mainly investigated the coupling effects of fly ash (FA) and corrosion on bond behavior. The impressed current method was utilized to achieve the target corrosion degrees. Three crucial factors that have impact on bond behavior was considered, which were FA content, corrosion degree and stirrups. The bond behavior was discussed using the bond‐slip curves. The results showed that the slight corrosion (less than 2.1%) can improve the bond behavior, the supplement of 15% FA can result in a higher ultimate bond strength and to a substantial extent offset the reduction in bond strength owing to the severe corrosion of rebar. The effects of stirrups on bond strength mainly focused on fly ash concrete (FAC) and had an almost negligible impact on ordinary concrete. The results and discussions can be of great significance to establish the bond‐slip constitutive model under multi‐factor coupling conditions and also can give some important advices to the design of engineering structures.

Deterioration of Mechanical Properties Steel Plate Due to Corrosion Phenomena-the Statistical Surveys of Full-Scale Ship and Electrochemical Model-Based Establishment

The mechanical properties of the corroded steel plates are important in analyzing the remaining capacity of ship structures. However, the data is scarce and most of that came from the simulated test with physical processing. In this study, the mechanical properties of the corroded steel plate from the real ship were investigated. Moreover, the mechanical properties declines model was constructed by conducting the tensile testing on the localized corroded and general corroded steel plate which were created by using the impressed-current method and corrected by the data from the real ships. The preliminary results showed that the young’s modulus, yielding strength, tensile strength and extension rate remains constant on the general corroded steel plates which have a reduced thickness from 5% to 35%. In localized corrosion, however, the extension rate decreases rapidly in prophase, and then the tensile strength decreases and the yielding plateau disappears. Also, the Scanning Electron Microscope (SEM) and X-ray diffraction (XRD) results revealed that the microstructures of the corroded steel plate from the real ship and simulated experiment are all same as the new plate, proving that the alternations of mechanical properties are the result from the corrosion-induced stress concentration.

Corrosion-induced shear performance degradation of reinforced concrete beams

Chloride-induced corrosion of reinforcement has been recognized as one of the most predominant causes of structural degradation. In this paper, experimental and numerical investigation was conducted to study the degraded shear performance of reinforced concrete beam. The corrosion of reinforcements, crack patterns, and structural behaviors of corroded specimens with various corrosion levels accelerated by the impressed current method were analyzed. The test results indicated that the corrosion-induced crack patterns have a close relationship with the level of reinforcement corrosion. Moreover, an obvious degradation of shear performance of corroded RC beams in terms of initial stiffness, cracking loads, ultimate bearing capacity, post-peak behavior, and energy dissipation capacity was observed, which became more pronounced as the corrosion level increased. When a severe corrosion level (ηa ≥ 12%) was encountered, the failure mode could even be changed from the shear-compression failure into a much more brittle diagonal splitting failure. In parallel, to numerically simulate the propagation of the main diagonal crack faithfully, the extended finite element method (XFEM) specified with an exponential softening traction-separation relationship was adopted. Moreover, to investigate the effect of corrosion-induced bond degradation, a user-defined element (UEL) was also developed to represent the interfacial bond response. The reasonable agreement between the numerical simulation and experimental results proved the feasibility of the proposed approach.

Assessment of corroded reinforced concrete beams: Cyclic load test and acoustic emission techniques

An acoustic emission (AE) technique has been used to monitor different initial conditions of corroded reinforced concrete beams under a cyclic load test (CLT) in accordance with ACI 437. Limited studies have assessed the validity of this test method for corroded reinforced concrete structural members, especially in a full-scale specimen. This study aimed to explore damage evaluation techniques based on CLT acceptance criteria and AE damage quantification techniques under different initial conditions of corroded reinforced concrete beam specimens. The beam specimens were subjected to three different corrosion durations (15, 30 and 45 days), to reflect the different extents of corrosion, which was accelerated using the impressed current method with 3.5% NaCl solution. This study also discussed the results obtained by both methods. Deviation from linearity (DFL) failed after loadset 3 based on the CLT acceptance criteria corresponding to the first visible crack in all of the specimens. The AE data analysis revealed that the cumulative signal strength (CSS) ratio was useful for identifying minor damage, whereas the felicity and calm ratios were suitable for determining moderate to heavy damage. Relaxation ratio analysis could be effectively performed to identify damage that corresponded to the first visible crack. Analysis on both methods showed that the DFL and relaxation ratio could be effectively used for damage identification because both methods corresponded to the first visible crack. Nonetheless, the AE method offered more advantages including damage detection and progression. Therefore, this method is promising for non-destructive evaluation in structural health monitoring.

Development of Sacrificial Anode Usable in High Specific Resistivity Solution by Parameter of Addition of NaCl

A sacrificial anode cathodic protection method has been widely used in the steel pile by galvanic current by potential difference between sacrificial anode and corrosive structural steel. And, the sacrificial anode cathodic protection method have generally merits compared to impressed current method because it can be applied to everywhere which is not connected with electricity. However, when the steel piles of the pier are submerged in low conductivity solution mixed with fresh water and sea water, the structural steel piles mentioned above have not been protected occasionally perfectively due to decreasing of galvanic current caused by deposited with oxide film on the surface of anode. In this study, five types of samples which are added with NaCl(g) to Zn anode were prepared with ratio of NaCl(g)/Zn(g)x100(%). And galvanic currents, surface morphologies characteristics of these samples was investigated using electrochemical methods such as polarization curves, galvanic current and analysis of surface morphologies before and after reduction weight ratio test in order to evaluate the effect of addition of NaCl(g) affecting to quality of zinc anode. The 2.6 % sample added with NaCl(5g) showed the highest value of galvanic current density in 0.8% NaCl solution, however, the highest reduction weight ratio was also observed at the 2.6% sample. Therefore, it is considered that the higher galvanic current density, the higher reduction weight ratio, that is, the life of sacrificial anode is shorted with increasing of galvanic current. Moreover, all samples added with NaCl(g) to Zn sacrificial anode indicated higher galvanic current density compared to the sample with no addition of NaCl(g) in low conductivity solution. Eventually, it is supposed that the galvanic current can be increased with addition of NaCl(g) to Zn sacrificial anode in low conductivity solution.

Investigating the spatial development of corrosion of corner-located steel bar in concrete by X-ray computed tomography

In this paper, the chloride-induced corrosion progression of a corner located steel bar in concrete is investigated by X-ray computed tomography (i.e., X-CT). Corrosion of steel bar is accelerated by placing the reinforced specimen in a wetting and drying cyclic corrosive environment, rather than by the impressed current method. 3D X-CT images are obtained and processed to characterize the different material phases, consisting of, steel bar, mortar, corrosion products and voids/cracks. The corrosion products expansion and concrete cracking are analysed and discussed. It has been found that pitting corrosion is prone to appear around the voids close to the steel bar, mainly due to the pre-existing supply of oxygen and moisture. In addition, a distinct transverse crack has been identified which is caused by non-uniform corrosion along the reinforcing steel bar. Within the cross-section, corrosion has also been found non-uniformly distributed, with the maximum rust layer pointing to the corner edge of the sample. Moreover, the corrosion rust distributions are used to parameterize a recently developed non-uniform corrosion model. This experimentally validated non-uniform corrosion model can be applied to corrosion-induced concrete cracking problems with confirmed accuracy. The combination of the use of wetting and drying cyclic corrosive environment and the X-CT scanning can provide a new method to the non-destructive investigation of corrosion process, rust distribution and corrosion-induced concrete cracking in the reinforced concrete structures.

Identification of incipient pitting corrosion in reinforced concrete structures using guided waves and piezoelectric wafer transducers

Corrosion poses a great threat to ageing civil infrastructure in the world, and researchers are seeking methods to monitor the corrosion in reinforced concrete structures. Detection of corrosion at its incipient stage has been an impending task in the non-destructive testing of materials. Several non-destructive testing methods to assess the presence of corrosion exist. The limitation of the current methods is that either they require measurement at several points or they require a large network of sensors. Guided wave-based monitoring overcomes these limitations because a large area can be scanned using fewer sensors. The process of corrosion is complex, and it leads to a simultaneous reduction in the diameter and the debonding between concrete and reinforcing steel bars in reinforced concrete structures. However, some of the recent studies that explore the use of guided waves focus only on the detection of the individual effect of diameter reduction and debonding of the rebars in reinforced concrete by artificially inducing the damage. In this study, an accelerated corrosion setup is deployed to induce pitting corrosion in reinforced concrete beams using the impressed current method. These beams are continuously monitored using ultrasonic guided waves that are generated and received by piezoelectric wafer transducers that are attached to the rebars. It is shown that the incipient stage of pitting corrosion can be detected successfully, and the mechanism of corrosion process, which involves the corrosion initiation, progression, and diameter reduction-and-cracking phases, can be established from the signal characteristics of the longitudinal and flexural-guided wave modes. The impressed current flow in the corrosion cell also confirms the various phases of corrosion.

Effect of grout conditions and tendon location on corrosion pattern in PS tendon in grout

Pre-stressed Concrete (PSC) has various engineering advantages like reduction of dead load, enhancement of shear strength, and reducing crack, however tendon corrosion in grout caused by deficient grout and intrusion of chlorides causes a tendon break and the related structural problems. It is important to understand the corrosion pattern varying with grout properties and placement conditions. In the work, TG (Tendon-Grout) systems are prepared considering grout quality, bleeding, tendon location, and crack width. In order to evaluate corrosion pattern in TG systems in a short period, ICM (Impressed Current Method) is adopted for corrosion acceleration for 2 and 4 days of duration. For two types of grout (conventional one and improved grout with reduced water to cement ratio and silica fume), corrosion current and its amounts are evaluated for various conditions. In the TG system with crack, corrosion greatly increases with extension of test duration for both types of grout since crack width on grout is a main channel for ion intrusion. In spite of crack effect, improved grout has better resistance to corrosion considering crack and bleeding condition. When TG system has eccentricity of tendon with small cover depth, no significant differences between conventional and improved grout are measured since cover depth is too small to protect chlorides from outside. Various effects like bleeding, crack, tendon location, and grout quality are discussed in the work. The improved properties in IG like porosity, strength, absorption ratio, and expansion rate are also investigated.

Non-uniform corrosion of steel in mortar induced by impressed current method: An experimental and numerical investigation

In this work, a new experimental method was proposed to rapidly induce non-uniform distribution of rust layers around steel bars in mortar and concrete. The proposed method is based on the impressed current method with short testing duration, but capable of inducing morphologies of rust distribution closer to those observed in natural corrosion environments than other existing methods. X-ray microtomography with image analysis techniques was implemented to quantify the rust formation and propagation in the proposed setups. A finite element model to systematically and semi-quantitatively investigate several experimental parameters (e.g., the distance between anode and cathode, the anode-to-cathode area ratio) was established and verified by a series of independent experimental programs.

A Study on Galvanic Current Variation of Zn Sacrificial Anode Made by Including of Additive in Solutions with Various Conductivities

There have been two cathodic protection methods to inhibit corrosion of the structural steel piles which are being immerged under seawater, or to control corrosion of a hull part of the ship exposed to sea water. One of them is a sacrificial anode cathodic protection method that the steel pile can be protected with galvanic current by potential difference between sacrificial anode and corrosive structural steel. And, the sacrificial anode cathodic protection method have generally merits compared to impressed current method because it can be easily applied to everywhere which is not connected with electricity. However, when the steel piles are being submerged in low conductivity solution mixed with fresh water and sea water, the structural steel piles mentioned above have not been protected occasionally perfectively due to decreasing of galvanic current of zinc anode caused by deposited with oxide film on the surface of anode. In this study, four types of zinc anodes samples which are included with three types of additives such as NaCl, KCl, and ZnCl2were prepared, and galvanic currents, the polarization characteristics of these anodes was investigated using electrochemical methods such as polarization curves, impedance, cyclic voltammogtam and galvanic current in order to evaluate the effect of additive affecting to quality of zinc anode. The sample added with NaCl indicated the highest value of galvanic current density compared to other samples in the case of lower and higher conductivity solutions such as 0.32 and 2.97mS respectively, and the sample added with KCl revealed the smallest galvanic current density in middle value of conductivities such as 1.53 and 2.27 mS. Moreover, Zn sample no added with additive exhibited the smallest value of galvanic current density in the lowest conductivities such as 0.32 and 0.98 mS. Therefore, it is considered that the galvanic current of the sacrificial anode can be increased by adding of additive when the anode is submerged in low conductivity solution mixed with fresh water and sea water.

Deterioration of shear behavior of corroded reinforced concrete beams

Steel bars in reinforced concrete (RC) structures may corrode in an aggressive environment, resulting in performance deterioration and premature failure. Stirrups begin to corrode earlier and faster than longitudinal steel bars due to their thinner concrete cover, and the shear strength decreases faster than the flexural strength. This paper presents an experimental investigation into the deterioration mechanism of shear behavior for corroded RC beams, and the prominent influencing parameters on shear behavior. The impressed current method was used to obtain corroded RC beams with different corrosion degrees in stirrups and longitudinal steel bars. Test results indicated that the beam may fail in shear instead of bending as the degrees of stirrup corrosion increases. The more severe the corrosion of stirrups was, the lower the shear strength. However, as the degree of corrosion increased in the longitudinal steel bars, the failure mode could change back to bending failure. The loss of bond strength affected the shear behavior of corroded RC beams, and the shear strength for bonded specimens was larger than unbonded ones. The shear strength decreased in beams with stirrups lacking end anchorages. Stirrups without end anchorages could still contribute to the shear strength if there was a good bond between stirrups and concrete. Otherwise, the stirrups could be ignored. With neither bond strength nor end anchorage, the beam could be treated as a beam without stirrups.

Structural behavior of corroded reinforced concrete beams under sustained loading

This paper presents the results of an experimental study designed to investigate the combined effects of corrosion and sustained loads on the structural performance of reinforced concrete beams. A total of eight RC beams, including both uncorroded beams and corroded ones accelerated by the impressed current method, were tested. All the beams were subjected to a four-point sustained bending load which was equivalent to 17%, 33% or 50% of the designed ultimate load, respectively. Corrosion degree, crack patterns, crack width and mid-span deflection of the beams were monitored during the test. The results showed that reinforcement corrosion had no obvious effect on the transverse crack spacing and a slight effect on the development of transverse crack width for the beams under simultaneous loading and corrosion. A higher load level and a lower current density allow for more sufficient oxidation of corrosion products with a larger volume expansion rate, leading to premature initiation and rapid propagation of corrosion cracking, and more obvious deflection development of RC beams. For a beam under simultaneous loading and reinforcement corrosion, the effect of reinforcement corrosion on its deflection cannot be ignored, because it may exceed creep effect at a relatively low corrosion degree.

Assessment of Fatigue Life for Corroded Reinforced Concrete Beams under Uniaxial Bending

An understanding of how corrosion affects fatigue behavior of reinforced concrete (RC) structures is essential for lifetime-oriented maintenance and design of existing bridges. This paper covers an experimental investigation on fatigue behavior of corroded RC beams. Corrosion in six RC beams was artificially accelerated by the impressed current method before fatigue loading was administered. All beams failed with fatigue fracturing of their tension steel bars. The fatigue test results indicated that the more severe the corrosion on steel bars was, the sooner the beams failed. The behavior of corroded steel bars determines the fatigue behavior of RC beams. This paper introduces a segmented linear model to simulate nonlinear behavior of corroded RC beams under fatigue loading, which was verified by experimental results. Of particular interest was the deterioration of corroded RC beams under fatigue loading, including the fatigue damage to concrete and corroded steel bars as well as the bond behavior between steel bars and concrete. The proposed model can simulate the development of strains in concrete and steel bars under fatigue loading, thereby permitting a fatigue life assessment. Further analysis investigated the effects of corrosion level, longitudinal variation of the cross-sectional areas, reinforcement ratio, load amplitude, and bond behavior as well. With the increasing degree of corrosion, load amplitude and longitudinal variation of the cross-sectional areas, or the decrease of the reinforcement ratio, the fatigue life of corroded RC beams decreased. The deterioration of bond behavior had little effect on fatigue life, but it led to a reduction in the flexural stiffness of beams.

Corrosion and Strength Behaviors in Prestressed Tendon under Various Tensile Stress and Impressed Current Conditions

Corrosion occurs more rapidly under high tensile stress and this leads to several problems like degradation of serviceability and structural performance in PSC (prestressed concrete) structures. In this paper, impressed current method, so-called ICM, was applied to tendons under tensile loadings of 0.0, 20.0, 40.0, and 60.0% of ultimate load. With induction of 20 volts for 24 hours to tendon under tensile stress, loading was induced to failure and the ultimate load was evaluated with varying corrosion behaviors. The changing mechanical behaviors in the same corrosive conditions were evaluated under different initial prestressing levels. With increasing initial prestressing load, corrosion occurred more rapidly and corrosion amount also increased linearly. The ultimate load accordingly decreased with increasing initial prestressing and corrosion amount. The relationships between prestressing levels and corrosion behaviors were quantitatively obtained through regression analysis. The measured current during applied voltage and the related corrosion amounts were also dealt with in this work.