Model-based prognosis for intergranular corrosion

Among the advantages of Aluminium-based alloys for structural use is their corrosion resistance. However, while Aluminium alloys are highly resistant to uniform (general) corrosion, they are much more susceptible to types of localised corrosion, especially intergranular corrosion, which is a localised attack along the grain boundaries which leaves the grains themselves largely unaffected. In order to estimate the progress of such corrosion in a given sample, it is considered possible to generate a numerical model of some sort. While there has been much effort spent in the development of electrochemistry-based models, the use of grey and black-box models remains largely unexplored. One exception to this is the use of Cellular Automata (CA) models which have recently been exploited to model the progression of uniform corrosion. The object of the current paper is to apply the CA methodology to the case of intergranular corrosion. The first phase of the work has been concerned with generating appropriate CA rules which can qualitatively reproduce observed physics, and this work is reported here. A model is proposed which shows qualitative agreement with experimental data on the advance of the corrosion front

Monitoring of carbon steel corrosion by use of electrochemical noise and recurrence quantification analysis

The corrosion of carbon steel in aqueous media resulting in uniform corrosion, pitting corrosion and passivation was investigated on a laboratory scale. Recurrence quantification analysis was applied to short segments of electrochemical current noise measurements. These segments were converted to recurrence variables, which could be used as reliable predictors in a multilayer perceptron neural network model to identify the type of corrosion. In addition, an automated corrosion monitoring scheme is proposed, based on the principal component scores of the recurrence variables. This approach used the uniform corrosion measurements as reference data and could differentiate between uniform and non-uniform corrosion

A New Model for Corrosion-induced Concrete Cracking

Corrosion of reinforced concrete is one of the major deterioration mechanisms which result in premature failure of the reinforced concrete structures. Due to the actual diffusion of chloride ingress, the corrosion products distribution is seldom uniform along the reinforcing bar. Recently, some non-uniform corrosion models have been proposed to investigate the corrosion-induced cracking mechanism of concrete. In this paper, a new corrosion model based on von Mises distribution is formulated and validated against experimental data. The developed model is then compared with the existing non-uniform models and the advantages are discussed. To demonstrate the application of the developed corrosion model, a concrete cover structure, containing aggregates, cement paste/mortar and ITZ, is simulated to predict the cracking phenomena of the concrete cover under different non-uniform coefficients in the developed corrosion model. It has been found that the non-uniform corrosion model can be used to simulate the realistic corrosion rust progression around the reinforcing bar, with the best accuracy. Moreover, parametric studies are conducted to investigate the effects of the basic factors formulated in the corrosion model on the surface cracking of the reinforced concrete structures

Similarity Analysis of Rebar Corrosion under Different Electrochemical Accelerated Method

The concrete cover cracking caused by non-uniform corrosion of reinforcing bar is one of the most important reason for structure service performance degradation. The most widely used electrochemical accelerated corrosion methods include external and internal electrode methods. The reinforcement are used as anode in both methods. The different between two methods is the position of auxiliary. In external electrode method, the auxiliary is set outside the specimen, including three methods, i.e. samples whole/part submerged in saline, samples wrapped by sponge and steel mesh. The electrochemical mechanism of these four accelerated method were analyzed by using the FE software COMSOL. According to the corrosion products distribution characteristic along the rebar circumference, the similarity of electrochemical accelerated and natural corrosion was presented. The results indicated that, rebar corrosion with external electrode method can be regarded as uniform corrosion; the internal electrode method could result in a non-uniform corrosion after optimizing, and the orientation and distance of rebar/electrode are two major influence parameters for accelerated non-uniform corrosion. In addition, based on the corrosion electrochemical principles, a modified internal electrode method was given. The stainless wire was put into the cylinder samples parallel to the rebar as a cathode. In present study, the rapid non-uniform corrosion method can play a positive role in studying the cover cracking process of reinforced concrete

Corrosion behaviour of steel rebar: effect of simulated concrete pore solution and chloride ions

In this work, we investigate the corrosion behavior of steel rebar (SR) in four simulated concrete pore solutions (CPS): NaOH+KOH (CPS1), Na2CO3 (CPS2), NaOH (CPS3) and Ca(OH)2 (CPS4) medium.  Effect of addition of Cl- anions as pollutant on pitting and uniform corrosion of SR is investigated by using potentiodynamic polarization (PDP) technic. The result obtained show that uniform and pitting corrosion of SR are strongly influenced by the nature of simulated CPS. In unpolluted CPS’s, only uniform corrosion of SR is observed in all cases. SR has excellent corrosion resistance in CPS4 compared to the other simulated CPS. In the polluted CPS’s by Cl- anions, we observe an accelerated uniform corrosion especially in CPS1, CPS3 and CPS4 mediums. The sensitivity to localized corrosion of SR varies from one simulated environment to another. It has the best resistance to pitting corrosion in polluted CPS3 medium. In CPS1 (pH = 13) and CPS2 (pH = 11.6) polluted by 3% NaCl, the tendency to pitting corrosion is the same. The localized attack is more pronounced in polluted CPS4 (pH=12.7). These results demonstrate that there are no limit values of the pH and the content of Cl- ions for the initiation of pitting and / or uniform corrosion. Therefore, it is the chemical composition of the simulated medium which imposes the pH value and the Cl- content for systematic corrosion study of the SR in the simulated CPS

Ultimate compressive strength of deteriorated steel web plate with pitting and uniform corrosion wastage

Steel structural members are likely exposed to corrosive environments, and thus corrosion is one of the dominant life-limiting factors of steel structures. Extensive studies on the effectsof pitting and uniform corrosion on the strength performance of steel structural members under a wide variety of loading conditions have been undertaken to assess the relationship between pitting corrosion intensity and residual strength. The aim of this study is to investigate the ultimate compressive strength characteristics of steel web plate elements with pit and uniform corrosion wastage. A series of ABAQUSnonlinear elastic-plastic large deformation finite element analyses are carried out on I-shapedsection steel girder models with varying pittingcorrosion intensities. Artificial pitting of different intensities is considered on the web plates and a uniform loading applied vertically on the upper flange section. The ultimate load-carrying capacity of deteriorated models with different levels of uniform thickness loss is also studied. The results are applied to assessing the ultimate compressive strength of web plates with different pitting corrosion intensities and a uniform loss thicknessby developing design formulae that represent the average loss thickness versus the ultimate load-carrying capacity

Effects of activated ceria and zirconia nanoparticles on the protective behaviour of silane coatings in chloride solutions

This work investigates the effect of CeO2 and ZrO2 nanoparticles on the corrosion protection performance of non-inhibited and cerium inhibited silane coatings in 3.5% and 5% NaCl solutions on electro-galvanized steel substrates. Atomic force microscopy (AFM) results show relatively uniform coating thickness and varying nanoparticle distribution depending on coating composition. The corrosion behaviour of the sol–gel coatings revealed that CeO2-ZrO2 nanoparticles reinforce the barrier properties of the silane films and seem to act as nano-reservoirs providing a prolonged release of cerium ions. This prolonged release of inhibitor from oxide nanoreservoirs confers longer protection to the metallic substrate