Reinforced Concrete Structure Performance in Marine Structures: Analyzing Durability Indexes to Obtain More Accurate Corrosion Initiation Time Predictions

This paper presents a comparison of six index properties collected during durability inspections of five Mexican seaports. Typical durability indicators such as compressive strength, saturated electrical resistivity, ultrasonic pulse velocity, percent total void content, capillary porosity, and chloride concentration profiles were analyzed to obtain empirical correlations with the non-steady-state chloride diffusion coefficient. These indices were compared to determine correlation coefficients that are the most important for obtaining better corrosion initiation forecasting. Two models of corrosion initiation time (ti) were used: Fick’s second law of diffusion and the reported UNE-83994-2 (Spanish Association for Standardization, UNE) in which electrical resistivity was used to calculate concrete service life. The data from both models were cleaned using correlated variables, and the initial variables were compared with ti. The main result achieved was the verification of the feasibility of using correlations of variables to clean unnecessary data in order to calculate ti. Additionally, electrical resistivity was identified as one of the main durability indexes for in-service concrete structures exposed to marine environments. This is important because electrical resistivity is a non-destructive and reliable test that can be measured both in the laboratory and in the field very easily.

Effect of Current and Coating Time on the Layer Thickness and Corrosion Rate of Electroplated AISI 1045

Corrosion mostly occurs on carbon steel which is applied for automotive components and household needs. This natural phenomenon is impossible to be avoided. However, it can be set by escalating its corrosion initiation time. Electroplating is a method that can be used to give protection to slower the corrosion initiation time by forming a layer on the specimen surface, additionally, this method is simple and low cost. One of the most commonly used metals for electroplating is nickel, nickel electroplating is suitable for automotive component coating. For these reasons, this study is focused on analyzing the effect of current and coating time on the layer thickness and corrosion rate of AISI 1045 carbon steel with nickel electroplating. The current variations used were 0.5; 1.0; and 1.5 A and the coating time variations were 5, 10, and 15 minutes. AISI 1045 was used as the cathode, nickel was as the anode, and nickel chloride was the electrolyte solution. The specimen with a current of 1.5 A and a coating time of 15 minutes shows the thickest coating and the lowest corrosion rate, with values of 0.0205 mm and 0.94 mpy, respectively. This study indicates that the increase of the current and coating time enhances the layer thickness and declines the corrosion rate.

INVESTIGATING THE CORROSION INITIATION PROCESS IN REINFORCED CONCRETE STRUCTURES UNDER THE IMPACT OF CLIMATE CHANGE

Introduction: Climate change (temperature rise and sea level rise) has a considerable influence on the behavior of concrete structures over time. All concrete degradation processes are connected to climate variables and the effects of climate change. The RCP8.5 (Representative Concentration Pathway) scenario, which is part of the report on climate change and level rise scenarios for Vietnam, predicts that the beginning of the 21st century will see an average annual increase in temperature between 0.8 and 1.1°C. In the mid-21st century, the temperature will likely increase by 1.8–2.3°C, with the temperature in the north likely increasing by 2.0–2.3°C and in the south by 1.8–1.9°C. In marine environments, the degradation of concrete structures can occur rapidly due to chloride-induced reinforcement corrosion. Furthermore, sea level rise is going to reduce the distance from the coastline to the structures and lead to increased surface chloride concentration. Methods: The evaluation of chloride penetration was based on the ASTM C1202 test (ASTM, 2012). The cylinder specimens (d = 100 mm, h = 200 mm) used for a rapid chloride penetration test (RCPT) were immersed in water for 28 days in a water-curing tank. Results: This study proposes a predictive model for analyzing the impact of climate change on the service life of concrete structures on Vietnam’s North Central Coast. The corrosion initiation time decreases by 16.5% when the effects of both temperature rise and sea level rise are taken into consideration. When only temperature rise is taken into consideration, the rate of reduction is approximately 9.0%. These results reaffirm that climate change has a significant effect on the corrosion initiation time of concrete structures located in a marine environment.

The Effect of Shape on Chloride Penetration of Circular Reinforcement Concrete Columns and Its Durability Design

The reinforced concrete (RC) circular element is usually simplified as slab one on the issue of chloride diffusion simulation, without considering the effect of the geometrical shape. In the paper, a modified slab diffusion model is proposed for circular section. A formulation for estimating the error caused by neglecting the effect of shape on chloride diffusion is derived. The formulation demonstrates that radius significantly affect the error. When shape is neglected, the effects of model parameters, including the diffusion coefficient, radius, cover concrete thickness and age factor, on the corrosion initiation time are investigated. The result shows the radius has a slight effect on calculating the corrosion initiation time compared with other model parameters. Furthermore, the influence of shape on estimating on reliability index for different service time is also discussed. A guideline is proposed for properly using the modified slab diffusion model instead of the original one to predict service life. Finally, the impact of the shape of the RC circular column on the durability design against chloride corrosion is studied. The design result when the column is simplified as a slab element indicates a lower required minimum concrete cover thickness. The minimum thickness should be improved by 5 mm as a conservative choice based on the result of the slab element.

Corrosion performance of steel reinforcement in concrete admixed with magnesium chloride and sulphate

Purpose Besides with a large amount of Na+ and Cl− ions in seawater, the presence of Mg+2 and SO4−2 ions builds more complex corrosion mechanism. This paper aims to investigate the corrosion of embedded reinforcement in concrete with the environment of both Cl− and SO4−2 anions associated Mg+2 cation. Design/methodology/approach The concrete specimens were prepared by using ordinary Portland cement (OPC), and OPC blended with metakaolin (MK) for water to cementitious material ratio (w/cm) 0.48 and 0.51. The concrete mixes were contaminated with the addition of MgCl2 alone and combined MgCl2 and MgSO4 in mix water. Reinforcement corrosion was evaluated by half-cell potential and corrosion current densities (Icorr) at regular intervals. Moreover, the influence of cementitious material type, salt type and w/cm ratio on electrical resistivity of concrete was also investigated. The statistical models were developed for electrical resistivity as a function of calcium to aluminium content ratio, compressive strength, w/cm ratio and age of concrete. Findings Although the corrosion initiation time increases in the concomitant presence of MgSO4 and MgCl2 as internal source compared to MgCl2, Icorr values are higher in both OPC and MK blended concrete. However, electrical resistivity decreased with addition of MgSO4. MK blended concrete performed better with increased resistivity, corrosion initiation time and decreased Icorr values. Originality/value This study reports statistical distributions for scattered Icorr of rebar in different concrete mixtures. Stepwise regression models were developed for resistivity by considering the interactions among different variables, which would help to estimate the resistivity through basic information.

Modeling the interaction between non-uniform corrosion of rebar and corrosion-induced cover cracking

<p>Circumferential non-uniform corrosion of rebars in concrete normally occurs in marine environment, and has an adverse impact on corrosion-induced cover cracking which may conversely change the circumferential corrosion profile. This paper investigates the interaction between chloride-induced non-uniform corrosion and corrosion-induced cover cracking. A chloride penetration model is introduced to predict the distribution of chloride content in concrete, which can determine the corrosion initiation time around the circumferential surface of a rebar. Subsequently, the time-dependent corrosion rate around the rebar surface can be calculated based on electrochemical theory, and then the corrosion profile at different time can be deduced. With the cross-sectional corrosion profile as an input, a mechanical model for corrosion-induced cover cracking can be utilized to simulate the development of surface crack, which has a significant influence on the diffusion of chloride ions and oxygen and may change the corrosion process. The derived model is verified with experimental results, and then a case study is conducted to demonstrate the time-varying non-uniform corrosion profile. Numerical simulation results indicate that, compared with uniform corrosion, non-uniform corrosion can lead to earlier cover cracking and faster development of surface crack width.</p>

Time-Variant Seismic Performance of Offshore RC Bridge Columns with Uncertainty

To establish a framework for evaluating the time-variant seismic performance of deteriorated reinforced concrete (RC) structures with uncertainty, offshore RC bridge columns exposed to marine environments are studied in this paper. The uncertainties from the material parameters, corrosion initiation time and earthquake ground motions are taken into account. Due to the different corrosion characteristics in various zones (i.e. the submerged zone, splash and tidal zone, and atmospheric zone) along the column height, corrosion-induced damages in each zone are considered separately, and the geometric mean of the yield displacements of the three zones is used to define the structural capacity (limit state). Meanwhile, the time-variant limit states are determined based on nonlinear static analyses, which reflect the current state of deteriorating RC columns. A total of four cases are studied using the Latin hypercube sampling (LHS) technique based on the probability distributions of the material parameters and corrosion initiation time, including the effects of statistical correlations among the material parameters. The results reveal that the seismic fragility is underestimated by a deterministic numerical model. The uncertainty in the corrosion initiation time influences the seismic fragility less significantly than that in the structural material parameters whether or not anti-corrosion measures are implemented. It is suggested that probabilistic methods should be used for seismic evaluation of deteriorating RC structures to consider the uncertainty involved.