Mass Loss Of Steel Research Articles

Probability of detection for corrosion-induced steel mass loss using Fe–C coated LPFG sensors

The traditional probability of detection (POD) method, as described in the Department of Defense Handbook MIL-HDBK-1823A for nondestructive evaluation systems, does not take the time dependency of data collection into account. When applied to in situ sensors for the measurement of flaw sizes, such as fatigue-induced crack length and corrosion-induced mass loss, the validity and reliability of the traditional method is unknown. In this paper, the POD for in situ sensors and their associated reliability assessment for detectable flaw sizes are evaluated using a size-of-damage-at-detection (SODAD) method and a random parameter model (RPM). Although applicable to other sensors, this study is focused on long-period fiber gratings (LPFG) corrosion sensors with thin Fe–C coating. The SODAD method uses corrosion-induced mass losses when successfully detected from different sensors for the first time, while the RPM model considers the randomness and difference between mass loss datasets from different sensors. The Fe–C coated LPFG sensors were tested in 3.5 wt.% NaCl solution until the wavelength of transmission spectra did not change. The wavelength shift of 70% of the tested sensors ranged from 6 to 10 nm. Given a detection threshold of 2 nm in wavelength, the mass losses at 90% POD are 31.87%, 37.57%, and 34.00%, which are relatively consistent, and the upper-bound mass losses at 95% confidence level are 33.20%, 47.30%, and 40.83% from the traditional, SODAD, and RPM methods, respectively. In comparison with the SODAD method, the RPM method is more robust to any departure from model assumptions since significantly more data are used. For the 90% POD at 95% confidence level, the traditional method underestimated the mass loss by approximately 19%, which is unconservative in engineering applications.

EFFECT OF REINFORCEMENT CORROSION ON THE PUNCHING SHEAR OF RC SLABS INCORPORATING MACRO SYNTHETIC FIBERS

This paper is part of an ongoing research on the effect of discrete fiber reinforcement on punching shear strength of reinforced concrete (RC) slabs subjected to accelerated corrosion regime of steel reinforcement. Results obtained from RC slabs incorporating macro synthetic fibers will be presented. Six RC slabs (1500 mm ×1500 mm ×100 mm) were prepared with a constant reinforcing steel ratio and incorporating synthetic fibers at different dosages (0.0 %, 0.5% and 0.75% by volume). The corroded set of slabs were subjected to an impressed current (IC) accelerated corrosion regime for 36 days with an applied constant current density of 500 µA/cm2. The slabs were subjected to wetting-drying cycles of 1 day wet and 2 days dry. During the wet cycle, the slabs were fully submerged in a 3.5% NaCl solution. The applied current results in a theoretical mass loss of steel by around 7%. The slabs were tested in a simply supported configuration until failure. The measured test parameters included the applied load, the slab deflection, and monitored the observed cracking. The results showed that reinforcement corrosion affected the slabs' performance in terms of strength and deflection capacities, as well as the cracking behavior. The load-deflection response showed that the addition of synthetic fibers could reduce the impact of steel corrosion on the punching shear behavior of the RC slab. Furthermore, the presence of synthetic fibers significantly limited the development of corrosion activity in the slabs by delaying corrosion-induced cracks when compared to the control slabs.

EFFECT OF REINFORCEMENT CORROSION ON THE PUNCHING SHEAR OF RC SLABS INCORPORATING MACRO SYNTHETIC FIBERS

This paper is part of an ongoing research on the effect of discrete fiber reinforcement on punching shear strength of reinforced concrete (RC) slabs subjected to accelerated corrosion regime of steel reinforcement. Results obtained from RC slabs incorporating macro synthetic fibers will be presented. Six RC slabs (1500 mm ×1500 mm ×100 mm) were prepared with a constant reinforcing steel ratio and incorporating synthetic fibers at different dosages (0.0 %, 0.5% and 0.75% by volume). The corroded set of slabs were subjected to an impressed current (IC) accelerated corrosion regime for 36 days with an applied constant current density of 500 µA/cm2. The slabs were subjected to wetting-drying cycles of 1 day wet and 2 days dry. During the wet cycle, the slabs were fully submerged in a 3.5% NaCl solution. The applied current results in a theoretical mass loss of steel by around 7%. The slabs were tested in a simply supported configuration until failure. The measured test parameters included the applied load, the slab deflection, and monitored the observed cracking. The results showed that reinforcement corrosion affected the slabs' performance in terms of strength and deflection capacities, as well as the cracking behavior. The load-deflection response showed that the addition of synthetic fibers could reduce the impact of steel corrosion on the punching shear behavior of the RC slab. Furthermore, the presence of synthetic fibers significantly limited the development of corrosion activity in the slabs by delaying corrosion-induced cracks when compared to the control slabs.

Inhibition resistance and mechanism of migrating corrosion inhibitor on reinforced concrete under coupled carbonation and chloride attack

Corrosion of steel bars in the marine environment is an important reason to reduce the service life of reinforced concrete structures. In this study, an amino alcohol migrating corrosion inhibitor (MCI) was coated on the concrete surface, which was then subjected to a simulated marine atmospheric environment by carbonation and salt spraying. The carbonation depth, chloride concentration of concrete, electrochemical performance of steel bars and mass loss rate of steel bar were determined to evaluate the corrosion inhibition performance of MCI. NELD-BS610 hardened concrete bubble spacing coefficient analyzer and scanning electron microscopy (SEM) were applied to analyze the pore structure parameters in concrete and the corrosion behavior of steel bar, respectively. The test results showed that MCI could alleviate the deterioration of concrete induced by accelerated carbonation and chloride attack, and delay the carbonation effect. After 7 days of accelerated carbonation and 35 days of chloride attack, the carbonation depth and chloride concentration of concrete coated with MCI were 16.07% and 16.93% lower than those of concrete uncoated with MCI, respectively. MCI could migrate to the steel bar surface of steel bar to form a protective film, significantly improving the electrochemical performance of the steel bar, and the inhibition efficiency of MCI was about 66.07 ∼ 97.91%. Besides, MCI could also reduce the mass loss rate of steel bars and porosity of concrete induced by carbonation and chloride attack. For the specimens coated with MCI, the mass loss rates of steel bar decreased by 20.31 ∼ 39.78%, and pores with sizes of 1.0 ∼ 0.2 μm in concrete reduced by 59.10 ∼ 76.38%. The results of this research are purposeful for alleviating the corrosion damage problems of reinforced concrete in marine areas.

Corrosion-induced cracking behavior of lightweight aggregate concrete: Experimental and numerical study

The corrosion-induced cracking potentially undermines the durability of concrete structures, while the fracture mechanism of lightweight aggregate concrete (LWAC) differs from that of the normal concrete subjected to expansive corrosion products due to the low-strength coarse aggregate. Eleven beams considering different diameters of LWA, the volume fraction of LWA, and surface crack widths were subjected to the accelerated corrosion setup, and the corrosion-induced cracks and steel mass loss were observed. The mesoscopic finite element model was established for the analysis of LWAC, and the model was verified according to the test results. The results of numerical study showed that decrease in the strength of LWA led to the inner damage of LWAC, while the increase in cover thickness made the cracking process of LWAC more rapid. On the basis of mesoscopic simulations, the critical cracking mass loss of steel bar and the empirical cracking parameter were derived, and then the linear equations were adopted for the establishment of relations between mass loss of corroded rebar and the corrosion-induced surface crack width by considering the effect of concrete cover and the rebar spacing.

Investigation of KNO2-KNO3-K2CO3 mixed molten salts with higher working temperature for supercritical CO2 concentrated solar power application

In the present work, the new eutectic composition of KNO2-KNO3-K2CO3 ternary salt for sCO2 solar thermal power generation is predicted by thermodynamic calculation, then the thermophysical properties of the eutectic salt are investigated by experiments combined with theoretical calculation, further studies are focused on its corrosivity. The results show that the predicted ternary molten salt is confirmed as 0.259KNO2–0.687KNO3–0.054K2CO3. Due to mixing a small amount of K2CO3, the upper limit of the operating temperature of the eutectic salt can reach 750.1 °C, and the melting point and the freezing point have a good thermal stability in the heating-cooling cycles. The calculated specific heat is lower than the measured one which can maintain at 1.407 J/(g·K) in the range of 400–450 °C. With the increase of temperature, the density decreases linearly and the thermal diffusivity tends to increase, thus there is a slight growing in thermal conductivity with an average value of 0.3 W/(m·K). The novel eutectic salt has an energy storage density of 865 MJ/m3. Although containing a low concentration of K2CO3, the eutectic salt shows low corrosion to 310S stainless steel. After the corrosion test of 240 h at 600 °C, the mass loss of stainless steel maintains a constant at 0.067 mg/cm2. The above results indicate that 0.259KNO2–0.687KNO3–0.054K2CO3 eutectic salt is a promising high-temperature thermal storage material for solar thermal power generation.

Experimental Design Considerations for Assessing Atmospheric Corrosion in a Marine Environment: Surrogate C1010 Steel

A rigorous assessment of marine atmospheric corrosion at a controlled NRL test site in Key West Florida was conducted. Certain factors which have been previously implicated in the literature as influencing the corrosion of engineering materials in atmospheric exposure were isolated and explored. In particular, the effect of sample size and orientation was explored. Low carbon steel (C1010) witness coupons were exposed in vertical non-sheltered, vertical sheltered, and tilted non-sheltered conditions. The effect of surface area on measured steel mass loss was also explored to identify the veracity of the so-called “edge effect”. Efforts were made to correlate meteorological atmospheric conditions (temperature, relative humidity, wind speed, wind direction, etc.) to the monthly assessment of corrosion damage. Results were assessed in terms of steel mass loss. Additive composite monthly corrosion damage tended to significantly overshoot the observed cumulative corrosion damage for samples exposed over the same period. This observation, among others presented herein, suggests that exposure of samples for less than 6 months is not an adequate predictor of long-term, natural exposure. Additionally, a smaller sample had a larger area-normalized mass loss than a larger sample. The influence of the sample edge (especially the bottom edge) was implicated in causing this difference.

Structural performance of deteriorating reinforced concrete structure

The structural behaviour of reinforced concrete structure with corrosion initiation in finite element modelling is studied in this paper. Structures in marine environments are vulnerable to corrosion, which leads to degradation of the concrete and steel. Reinforcement corrosion leads to multiple damages to the structures such as spalling which is parallel to the direction of steel reinforcement resulting in change in the sectional properties of the steel bars. The degradation in the material properties due to corrosion intend to reduction in bond strength and increases crack width. Several tests were performed and various empirical formulas were proposed by the researchers on corroded members. Researchers experimented under different exposure conditions with respect to time was used to find the performance of structure for 0,10,20,30,40,50 years of corrosion and the structure with addition of 50 years steel mass loss. They validated and concluded that the structural losses its strength as the corrosion increases and also loss of base shear and tension in the members which tends to collapse of the structure for the minimum seismic loads. Structures with a thirty-year rise in steel mass loss and concrete strength have improved the structure's strength up to 25 % in base shear and 22 % in displacement for seismic analysis. The present study is applicable for the structure in the marine environment with a less seismic load.

Understanding the role of alloyed Ni and Cu on improving corrosion resistance of low alloy steel in the simulated Beishan groundwater

• The addition of Ni and Cu elements significantly inhibited the cathodic and anodic processes of steel corrosion. • Ni and Cu alloy elements were obviously enriched in the inner rust layer, which could improve the compactness of rust layer. • Fe 6 (OH) 12 SO 4 stably existed in the corrosion products of NiCu steel because Ni(Ⅱ) or Cu(Ⅱ) could substitute Fe(Ⅱ) of Fe 6 (OH) 12 SO 4 and increase its oxidation resistance. • Ni and Cu made Fe3O4 ionic selective by doping, which could repel the aggressive anions and improve the corrosion resistance. The corrosion behavior of NiCu low alloy steel and Q235 low carbon steel as the candidate materials for geological disposal containers of high-level radioactive waste in the simulated Beishan groundwater was comparatively studied by weight loss test, electrochemical measurements, scanning electron microscope (SEM), electron probe microanalysis (EPMA), X-ray diffraction (XRD), Raman spectrum and X-ray photoelectron spectroscopy (XPS). The electrochemical results showed that the corrosion potential of NiCu steel and Q235 steel gradually increased with the immersion time. Simultaneously, the cathodic process transited from hydrogen evolution reaction (HER) control to the rust reduction control, while the anodic process was always dominated by the active dissolution of iron. By comparison, both the cathodic resistance and the anodic dissolution resistance of NiCu steel corrosion were apparently higher than that of Q235 steel. The results of rust layer characterization indicated that Ni and Cu elements could be enriched in the inner rust layer of NiCu steel and the rust layer was more compact. As the main corrosion products, the content of α-FeOOH in the rust layer of NiCu steel was obviously increased more than that of Q235 steel. Fe 6 (OH) 12 SO 4 stably existed in the corrosion products of NiCu steel because Ni(II) or Cu(II) could substitute Fe(II) of Fe 6 (OH) 12 SO 4 and increased its oxidation resistance. Moreover, Ni and Cu could also make Fe 3 O 4 ionic selective by doping. After the long-term immersion, the corrosion mass loss of NiCu steel was significantly lower than Q235 steel, which further confirmed the benefits of Ni and Cu alloying on improving the steel corrosion resistance.

Long-term corrosion and stress corrosion cracking of X65 steel in H2O-saturated supercritical CO2 with SO2 and O2 impurities

In this study, four testing cycles (total 480 h) were conducted to investigate corrosion and stress corrosion cracking (SCC) of X65 steel in H2O-saturated supercritical CO2 (s-CO2) containing SO2 and O2 impurities. The results showed that X65 steels experienced severe corrosion and formed a porous corrosion layer composed of iron sulfates, carbonates and oxy-hydroxides. Increasing time from 120 to 480 h resulted in the shift of dominant corrosion products from iron carbonates to iron oxy-hydroxides due to acid regeneration cycle. The mass loss of X65 steel almost linearly increased with exposure time, indicating a nearly constant corrosion rate in the s-CO2 environment. In comparison with previous studies, timely replenishing s-CO2 fluid in a static autoclave is crucial to accurately determine the long-term corrosion kinetic of pipeline steel. Based on literature survey and current study, several factors (SO2 content, H2O content, addition of NO2) affect the long-term corrosion rate in s-CO2 environments, and a power-function-based empirical model is purposed to depict the long-term corrosion rate of X65 steel in H2O-saturated s-CO2 + O2 + 100/2000 ppm SO2. The long-term SCC assessments showed that the SCC susceptibility of X65 would be still quite low, which might be related to the O2-depressed hydrogen cracking and/or the lack of localized stress concentration.

Bayesian Network Machine Learning Approach to Atmospheric Corrosion Modelling

The performance degradation of materials exposed to corrosive atmospheric environments is a serious problem. Corrosion maintenance strategies and cycles are informed largely by historical trends in corrosivity dependent on the location of interest. Assessments are often made with sparse experimental data and are generalized to certain materials and baseline conditions observed in the past. The development of a predictive model which can better inform maintenance strategies and cycles offers opportunities for time savings and cost avoidance. Such a model would need to predict corrosion damage accumulation as a function of material of interest, location of interest, and atmospheric conditions during the period of exposure of interest.Machine learning has recently gained attention as a way to model complex systems and processes. Atmospheric corrosion is certainly a complex process as there are many parameters that influence it which are uncontrolled and vary in difficult to predict ways. A machine learning algorithm would require data to learn from which might include environmental conditions such as temperature, relative humidity, UV light exposure, time of wetness, salt concentration, applied loads, and electrochemical data for substrates, inhibitors, and coatings. The ability of machine learning to determine models and relationships from large data sets is well demonstrated; however, a Bayesian model approach can be more suitable when data is limited, expensive or time consuming to obtain, and expert knowledge can be leveraged to construct the relationships. While certain meteorological variables are well categorized and easy to retrieve other variables like corrosion damage or salt deposition are sparsely reported if measured at all. For this reason, a Bayesian Network Model has been developed to better predict the corrosion damage accumulation of C1010 steel and three different aerospace coating systems applied over AA2024-T351.The network map was constructed from parameters (nodes) which are known to influence corrosion. Mathematical relationships were used to develop relationships between nodes or to calculate new nodes as available. Finite element analysis was used to refine the network map and provide supplemental inputs for features that are difficult to measure experimentally. The model was initially trained from historic corrosion data gathered from collaborators across the DoD. Contemporary experimental data was also gathered in a 19-site survey of field exposure sites across the world. This dataset provided further inputs for training and also data for validation and testing. The methodology behind model construction will be highlighted and model predictions will be compared against experimental results. To date, there has been good correlation between model predictions and experimental results for C1010 steel mass loss, which provides a basis to further extend the model to aerospace coating systems. Figure 1

Bond behavior of NSM strips in corroded/cracked reinforced concrete

There is limited research on the bond behavior of NSM strips embedded in corroded/cracked reinforced concrete (RC). Therefore, this study was initiated to evaluate the bond behavior between corroded/cracked RC and NSM strips. The test specimens consist of two concrete prisms (reinforced and plain) mounted from two opposite sides with NSM strips. After 28 days of moisture curing, twenty-four specimens were immersed in saline solution and were exposed to three accelerated corrosion levels with steel mass loss of 2.2, 4.1 and 8.1%. The bond behavior was evaluated using double shear pullout test. The study showed that the corrosion cracks increased with the increase of corrosion level. The maximum crack width reached 0.91 mm at corrosion level 3. The mass loss of the corroded reinforcing steel increased from 2.1% for corrosion level 1–8.3% for corrosion level 3. The bond strength between NSM strips and corrosion cracked concrete was significantly decreased with maximum reduction of 48% at corrosion level 3. The other bond characteristics including maximum slip, bond toughness and bond stiffness were also decreased with corrosion with percent reduction of (31, 67 and 35%), respectively. The failure mode of the bond between NSM strips and corrosion cracked concrete was splitting of concrete. Theoretical models were proposed for predicting the bond strength between NSM strips and corrosion cracked concrete based on corrosion level and crack width. The proposed models showed excellent agreement with the experimental results from the current study and the literature.

Durability and Property Study of Decade Old Crumb Rubber Concrete Cored Specimens.

Crumb rubber concrete (CRC) is a concrete that contains rubber crumbs. This article presents a study of three experiments on long aged CRC specimens that were cored from a decade old CRC bridge deck in Tianjin, China. The three experimental tests conducted were: (1) the flexural stress–strain test on semi-circular disk specimens; (2) the accelerated steel-rebar corrosion test and (3) the carbonation test. In addition, the in situ carbonation test was also carried out on the CRC bridge deck. The flexural stress–strain test results showed that the CRC semi-circular disk specimens exhibited a ductile pattern and high-energy absorbing capacity with its flexural tensile strength being at 5 MPa and the flexural modulus of 10 GPa. The steel corrosion rust rate via the calculation of steel mass loss before and after the test in the accelerated steel-rebar corrosion test remained extremely low. The carbonation test results showed that in comparison with the prediction of two popular carbonation models, the carbonation in the CRC bridge deck took place at a much slower rate during the last 13 years. All of the results obtained in this study are reported for the first-time and indicate that these CRC cored specimens exhibit good mechanical properties and excellent durability characteristics after a decade in service, which may provide the technical knowledge for the possible future application of CRC in concrete constructions.

Influences of pre-bending load and corrosion degree of reinforcement on the loading capacity of concrete beams

AbstractIn this article, experimental studies on the flexural behavior of concrete beams with corroded reinforcement were conducted. The beams were subjected to simultaneous different load levels and immersed in NaCl solution for 30 days with accelerated corrosion. A four-point bending test was subsequently carried out to determine the loading capacity of these beams. Experimental data show that the loading capacity of the beam decreases as the level of preload increases. The mass loss of steel bars in the beams increases as the level of preload increases. The loading capacity and steel mass loss of the beams subjected to 0.8 of failure load of the non-corroded beam decrease by 32.7 and 30.3%, respectively. The numerical investigation was also done to evaluate the loading capacity with various corrosion degrees of steel bars.

Effect of macrocell currents on rebar corrosion in reinforced concrete structures exposed to a marine environment

Autonomous corrosion monitoring systems in reinforced concrete structures tend to use sensors that are electrically isolated from rebars. This monitoring strategy ignores the macrocell currents that take place between active and passive areas of reinforcement. The effect of these currents has been studied on rebar corrosion in structures exposed to a marine environment. The results showed the existence of macrocell currents generates greater anodic polarisation in rebars’ active areas, which favours chloride migration towards steel surface. As a result, corrosion onset takes place sooner, the concentration of the chlorides is higher, and the corrosion rate increases. When a rebar is in passive state, steel mass loss is negligible due to macrocell currents. However, after corrosion onset, the influence of these currents is greater the worse concrete quality is, and the smaller cover is. The corrosion rate showed differences of almost two orders of magnitude in concrete C30 and of one order of magnitude in concrete C50. When the total corrosion rate is determined only by measuring microcell currents, the obtained values tend to underestimate the mass loss due to corrosion by 90%. Conversely, when the analysis includes macrocell currents, a good fit between the theoretical and real values is obtained.

Study on the microstructure and properties of iron-based composites locally reinforced by in-situ submicron TiC particles

This study discussed the strengthening mechanism of in-situ submicron TiC particles on high chromium cast iron matrix composites. By changing the Ti content, the microstructure evolution and performance change law of the composites are analyzed. The results show that the average particle size of the TiC particles will grow with the increase of the Ti content in the preforms. After the in-situ reaction, there will be a transition layer of 20–30 μm in the interfacial zone of the composite, and a high density of dislocations will appear at the same time. Furthermore, the presence of submicron TiC particles in the microstructure can significantly improve the strength and wear resistance of the composites. By contrast, only the Ti content in preforms is 50%, the microstructure and performance of the test steel (S2 steel) are the most ideal. The TiC particles in the composite area account for more than 70%, and the hardness is as high as 1236 HV, which is more than twice the hardness of the matrix. Under the same wear conditions, the mass loss and wear rate of S2 steel are the smallest, which are only 0.2 ± 0.1 mg and 3.08 × 10−6 ± 0.05 mm3/Nm, respectively.

Reinforcement corrosion of circular concrete columns under sustained load

This paper presents the results of an experimental study of the axial capacity of circular spirally-reinforced concrete columns that were subjected to accelerated corrosion while sustaining a constant compressive service load. Two sets of columns of five columns each were designed with different spiral pitch to investigate the effect of concrete confinement on the corrosion propagation. Columns with non-confining spiral reinforcement had only their longitudinal reinforcing steel corroded, whereas in the other set of specimens, the spiral reinforcement was corroded and isolated from the vertical reinforcing steel. The cracking initiation, pattern, and widening of the concrete cover were monitored for a period of 4-10 months, and relations obtained between the crack widening and propagation and the elastic shortening of the column and steel mass loss were established. After the accelerated corrosion period, eight columns were tested to failure under either concentric or eccentric load; the vertical deformation, cracking pattern and failure type were monitored and recorded. The failure of specimens with non-confining spiral reinforcement was characterized by sudden crushing of the concrete and longitudinal reinforcement buckling, with a reduction in load capacity of 30-40%. Columns with confinement reinforcement failed in a ductile manner by progressive spalling of the concrete cover, maintaining their load capacity in spite of the corroded spiral reinforcement.

Investigating the effects of anti-corrosive coatings on the bond between corrosion-damaged rebar and concrete repair materials

Reinforcement corrosion causes destruction to the steel by a loss in cross section and rib height, which can affect the bond between steel and concrete. During repair of corrosion-damaged reinforced concrete members, a protective coating is usually applied to the cleaned corroded steel. There is, however, little information available on the bond performance of repair coatings. Furthermore, the effect of their coating thickness and other parameters like rebar diameter, corrosion degree and repair material properties are not well understood when considered in parallel with repair coatings. This paper seeks to contribute towards understanding the use of anti-corrosive coatings and the influence of their thickness on the bond between cleaned steel reinforcement and repair materials, when used in combination with different bar geometries at varying degrees of corrosion damage. In this investigation, two high tensile steel bars, Y12 and Y16, were considered. Rebar corrosion damage levels of 0%, 10% and 20% (of steel mass loss) were simulated by mechanical grinding of sound rebar samples to represent the condition of cleaned corroded rebar. A commercially available epoxy-modified, cementitious coating material was applied to the steel in one or two coats, with each coat being 0.6 mm thick. Three repair materials with CEM I 52.5N were considered in this study, which included one concrete with a w/b ratio of 0.45 and two mortars with w/b ratios of 0.47 and 0.65. Pull-out testing was conducted on 108 specimens, and the results analysed by means of the one-way ANOVA test to assess the effect of mainly coatings and other parameters on the bond. The results indicate applying coatings to 10% and 20% corroded steel does not significantly reduce the bond for the M65 and C45 mixes. Furthermore, the difference between one and two coats had little influence on the bond of corroded steel for all rebar geometries and repair mixes.

Probabilistic assessment of time to cracking of concrete cover due to corrosion using semantic segmentation of imaging probe sensor data

This paper presents a framework for segmentation of imaging probe corrosion sensor data using a deep learning algorithm and estimation of the remaining service life of the structure using the segmented data. The sensor consists of a sacrificial metal foil that is imaged using the optical probe and the changes in the images as corrosion develops can be used as a proxy to monitor the condition of the concrete. In this paper, DeepLabV3+ which is a deep learning network architecture is implemented for the segmentation of sensor images. The neural network model trained on labeled corroded and uncorroded images of foil captured under various chloride levels yields a test accuracy of 95%. The mass loss of steel is estimated using a Bayesian curve fitted over the estimated mass loss from the segmented images and the mass loss from the accelerated corrosion test. This is then used for the estimation of the corrosion rate, which is given as the input for the probabilistic estimation of the time at which the concrete cover is expected to crack. A case study is presented to demonstrate how the segmented images from the neural network model can be used for estimating the time to cracking of concretes.

Corrosion resistance of fiber-reinforced geopolymer structural concrete in a simulated marine environment

The corrosion resistance of fly ash-based geopolymer structural concrete (GPC), with or without fibers, was investigated in a simulated marine environment, and compared with that of ordinary Portland cement structural concrete. The corrosion behavior is studied through an electrochemical method for inducing accelerated corrosion. The fiber reinforced beam specimens contained polyolefin fibers in the amounts of 0.1%, 0.3%, and 0.5% by volume. Several artificial corrosion conduits were introduced into the specimens reaching up to the rebars. This process enhanced the rate of laboratory corrosion in GPC, thus allowing faster and measurable evaluation of corrosion resistance. The corrosion-damaged beams were then analyzed through a method of crack scoring, and determination of steel mass loss and residual flexural load capacity. The fiber reinforced corroded GPC beams (with 0.1–0.5% fibers) showed a 24% reduction in crack scores, and a 109% increase in residual flexural load capacity, compared to unreinforced corroded GPC beams. This shows promise of fiber-reinforced GPC as a sustainable structural material in the marine environment.