Concrete Pore Water Research Articles

Estimation of Some Parameters in the Point Defect Model (PDM) for the Passivity of Metals

In this paper, we justify that the potential drop at the barrier layer/solution (bl/s) interface of the barrier layer of the passive film on a metal, φf/s, is a linear function of the applied voltage V and pH in the case of sufficiently thin barrier layer. Furthermore, we show that a relationship exists between parameters α (the dependence of φf/s on V) and β (the dependence of φf/s on pH), that is, those parameters are not independent, in the general case. It is also shown that some dependence of parameters α and β on temperature can exist. However, this dependence in the practical region (0 °C–100 °C) is weak and, in many cases, it is possible to neglect the dependence of parameters α and β on temperature. Finally, we show that it is possible to estimate, theoretically, the parameter β (and accordingly parameter α) by using models for specific systems. For the system considered in the current report (carbon steel in concrete pore water), the estimated value of parameter β is confirmed experimentally. These findings are discussed in terms of the electronic and point defect structures of the barrier layer.

Dissolution behaviors of PuO2(cr) in natural waters

PuO2(cr) dissolution in natural water was investigated at 25°C and 60°C under atmospheric conditions. The concentration of Pu in solutions [Pu], was monitored for 1 year of reaction time. PuO2(cr) dissolution in natural water reached a steady state within 2 months at 25°C. The [Pu] in groundwater and seawater at pH 8 were in the range of [Pu] = 0.9–34 and 3.4–27 nM, respectively. The [Pu] in concrete porewater (rainwater equilibrated with concrete) at pH 8.1–10.9 was in the range of 0.1–3.2 nM. The [Pu] and pH values of groundwater were similar to those of seawater samples having a high ionic strength. The measured [Pu] at equilibrium in all samples was higher than the calculated solubility curves for PuO2(am, hyd). Experimental evidence is insufficient to confirm the oxidation state of Pu in solution and solid phases. However, the results of geochemical modeling indicate that PuO2(am, hyd) and aqueous Pu(IV) species are dominant in natural water samples of this work. The dissolution behavior of PuO2(cr) in natural waters is comparable to the oxidative dissolution of PuO2(am, hyd) in the presence of PuO2(coll, hyd). The dissolution of PuO2 in groundwater decreased at higher temperatures, whereas the influence of temperature in seawater and porewater was not significant under these experimental conditions.

Prediction of frost resistance of concrete at different freezing temperatures

The article proposes a method for evaluating the frost resistance of concrete at actual operating temperatures, using measurement results at temperatures that are regulated by current standards. Frost resistance was evaluated by determining the amount of water freezing at different temperatures, based on the measured adsorption isobars and the obtained relationship between the freezing temperature of water in concrete pores and relative humidity. A comparison of the calculated values of the frost resistance of concrete with those got based on direct measurements showed the adequacy of the calculation model. The proposed experimental-analytical method for evaluating the frost resistance of concrete at different freezing temperatures allows in a small amount of time to get more complete information about the behavior of the material in frosty weather under real operating conditions than is provided for by existing methods. An analysis of the dependence of frost resistance on temperature also makes it possible to identify the temperature regions where it changes most strongly, and to shift, if necessary, these regions to lower or higher temperatures due to the change of the composition and technology of concrete production.

The effects of organic corrosion inhibitor on concrete properties and frost resistance

Organic compounds are widely used as organic corrosion inhibitors (OCIs) for inhibiting chloride-induced corrosion in reinforced concrete. However, the effects of these organic compounds on concrete properties are unclear. In this paper, the effect of three types of commonly-used organic corrosion inhibitors (easter-, alcoholamine-, and carboxylic acid-based) on pore size distribution, hydration products, and microstructure is analyzed using the nuclear magnetic resonance (NMR), X-ray diffraction (XRD) and scanning electron microscope (SEM). Moreover, the mechanical properties, surface scaling resistance, and capillary absorption of OCIs-modified concrete after exposure to salt-frost cycles are also investigated. The obtained results show that the used OCIs do not affect the hydration product species. Easter-based OCIs can significantly decrease the proportion of larger pores, thus enhancing the compressive and reducing the capillary absorption rate. Concrete frost resistance has shown improvement after adding alcoholamine-, and carboxylic acid-based OCIs. However, easter-based OCIs may induce severe surface scaling by increasing the saturation of concrete pore water. The obtained results provide an experimental basis guiding the application of OCIs in cold regions.

Reactive Transport Simulation of Low-pH Cement Interacting with Opalinus Clay Using a Dual Porosity Electrostatic Model

Strong chemical gradients between clay and concrete porewater lead to diffusive transport across the interface and subsequent mineral reactions in both materials. These reactions may influence clay properties such as swelling behaviour, permeability or radionuclide retention, which are relevant for the safety of a radioactive waste repository. Different cement types lead to different interactions with Opalinus Clay (OPA), which must be understood to choose the most suitable material. The consideration of anion-depleted porosity due to electrostatic repulsion in clay modelling substantially influences overall diffusive transport and pore clogging at interfaces. The identical dual porosity model approach previously used to predict interaction between Portland cement and OPA is now applied to low-alkali cement—OPA interaction. The predictions are compared with corresponding samples from the cement-clay interaction (CI) experiment in the Mont Terri underground rock laboratory (Switzerland). Predicted decalcification of the cement at the interface (depletion of C–S–H and absence of ettringite within 1 mm from the interface), the Mg enrichment in clay and cement close to the interface (neoformation of up to 17 vol% Mg hydroxides in concrete, and up to 6 vol% in OPA within 0.6 mm at the interface), and the slightly increased S content in the cement 3–4 mm away from the interface qualitatively match the sample characterisation. Simulations of Portland cement—OPA interaction indicate a weaker chemical disturbance over a larger distance compared with low-pH cement—OPA. In the latter case, local changes in porosity are stronger and lead to predicted pore clogging.

Influence of the formwork removal by polarization on the facing aesthetics in reinforced concrete

Formwork removal by means of polarization offers an alternative solution to compensate for some of the disadvantages and risks of using mineral-based oil due to its petrochemical origin. This technique consists of applying an electrical current between the steel reinforcing bars and the metal formwork wall in order to obtain a thin water film at the concrete/formwork interface and allow for formwork removal. This paper focuses on the facing quality of the reinforced concrete and formwork surface at various temperatures for both conventional and self-compacting concretes. A series of experimental tests have been conducted in the laboratory to determine the optimal polarization parameters (voltage value, time and duration of its application). On-site tests were then performed to observe the scaling effect. Results indicate that the proposed polarization technique can indeed provide an effective means to separate the concrete from its formwork without requiring demoulding oil. Concrete mixtures implemented both in the laboratory and on-site display high-quality facing without the presence of any attachment points. A chromatographic analysis of the concrete pore solution and water transported by electro-osmosis shows that ion concentrations remain unaffected. This polarization approach can thus be used as an alternative to avoid the use of oils of a chemical or petrochemical origin.

(Invited) Admittance Analysis of Passive Film on Rebar in Solution Simulating Concrete Pore Water

Steel corrosion is suppressed in concrete because the passive film is formed on the steel surface of rebar owing to the strong alkaline environment inside the concrete. Dawson et al. [1] reported that the corrosion state of steel rebar in concrete can be evaluated by the charge transfer resistance, R ct, estimated from impedance spectrum. In order to estimate R ct from impedance spectrum, they [1] proposed an equivalent circuit which includes the solution resistance R sol, R ct, electric double layer capacitance C dl, and Warburg impedance Z w. An interfacial resistance at rebar/concrete interface was defined as R ct in the report [1], whereas the authors consider that this interface resistance should be a passive film resistance R f when passive film is formed on rebar and the interface resistance is very large. It is often difficult to estimate R f under conditions where the passive film is formed on the rebar surface of the rebar because the impedance locus in the low frequency range does not converge to the real axis of Nyquist plane due to the large value of R f. In this study, the precise determination method of R f by the admittance is proposed.The electrochemical impedance measurement was carried out by a three-electrode system. A rod of carbon steel was adopted as a working electrode. The carbon steel used in the present study has the same composition as rebar which is normally used in actual reinforced concrete structures in Japan. A platinum wire and a saturated KCl silver/silver chloride electrode were used as counter and reference electrodes, respectively. A potentio/galvanostat (Solartron, 1287) and a frequency response analyzer (Solartron, 1255B) were used as measuring devices. In the impedance measurement, the measurement frequency range was from 10 mHz to 10 kHz, the DC potential was corrosion potential, and the AC potential amplitude was 10 mV. A saturated calcium hydroxide solution was used for the test solution to simulate the concrete environment. The pH of test solution was about 12.5.The impedance spectrum of rebar described a part of semicircle on Nyquist plane. Because the impedance locus in the low frequency range did not converge to the real axis, it is necessary to extrapolate a semicircle from the partial semicircle for the estimation of R f. The plots of admittance showed a clear semicircle and converged to the real axis in the low frequency range. As high and low frequency limits of admittance correspond to 1 / R sol and 1 / (R sol + R f), respectively, on the real axis of the complex plane, the R f can be estimated directly from the plots of admittance on the complex plane. The present results suggested that the proposed method can be applied to estimate R f of rebar in concrete more accurately. Reference [1] J. L. Dawson, L. M. Callow, K. Hladky, and J. A. Richardson, Proceedings of NACE Corrosion/78, Paper No. 125 (1978).

Overview of anaerobic corrosion of carbon steel radioactive waste packages in alkaline media in support of the Belgian supercontainer concept

AbstractThe so‐called supercontainer concept is currently being considered as the reference design for the final disposal of vitrified high‐level radioactive waste and spent fuel in Belgium. It comprises a prefabricated Portland cement‐based buffer that completely surrounds a carbon steel overpack. In this highly alkaline environment (pH ~13.6), and under normal conditions (i.e., without the ingress of aggressive species), the carbon steel overpack will be protected by a passive oxide film, which is expected to result in very low uniform corrosion rates. Considering the long timescales applicable to waste disposal, determining accurate and reliable estimates of the uniform corrosion rate under anoxic conditions forms a very important part of the safety and feasibility strategy. It is also crucial to demonstrate that no other form of corrosion apart from uniform corrosion takes place. This paper presents the progress of the research that has been made since the LTC2016 Workshop (Toronto, Canada) on uniform corrosion, pitting corrosion and stress corrosion cracking behaviour of P355 QL2 grade carbon steel exposed to an artificial concrete pore water solution.

Determinant factor for dynamic equilibrium of transformation between vapor in atmosphere and water in concrete

Under certain conditions, liquid water in concrete pores can evaporate, forming vapor to the surrounding atmosphere; vapor in the surrounding atmosphere can condense, forming liquid water in concrete pores. Therefore, there exists a water-to-vapor transformation causing change of liquid water content in concrete. This study is aimed at analyzing the determinant factor for the water-to-vapor transformation based on the responses of relative humidity in concrete to different relative humidity and temperature of the surrounding atmosphere. Relative humidity in concrete was measured with two temperature and humidity (T&RH) probes (One was embedded into concrete and the other was placed in the cavity formed by embedding a PVC pipe) under two conditions: (1) constant temperature and variable relative humidity of the surrounding atmosphere (2) constant relative humidity and variable temperature of the surrounding atmosphere. Moreover, a specially designed device was adopted to verify the determinant factor for the water-to-vapor transformation. The results showed that relative humidity recorded by the embedded T&RH probe was always 100%, while that recorded by the placed T&RH probe had responses to the surrounding atmosphere under conditions (1) and (2). According to the results, the determinant factor for the water-to-vapor transformation is vapor partial pressure, namely absolute humidity, of the surrounding atmosphere. Furthermore, as long as there is liquid water in concrete, vapor in concrete pores is in saturation state, indicating the internal relative humidity of concrete should be a constant of 100%. Consequently, relative humidity in the cavity is inaccurate to represent moist condition of concrete.

Evaluation of the frost resistance of concrete in real operating conditions

The article proposes a method for evaluating the frost resistance of concrete at actual operating temperatures, using measurement results at temperatures that are regulated by current standards. Frost resistance was evaluated by determining the amount of water freezing at different temperatures, based on the measured adsorption isobars and the obtained relationship between the freezing temperature of water in concrete pores and relative humidity. A comparison of the calculated values of the frost resistance of concrete with those got based on direct measurements showed the adequacy of the calculation model. To get information about the frost resistance of concrete during unilateral freezing, a conductometric method was used to determine the kinetics of moisture diffusion and ice formation. It is shown that the use of this method allows one to establish the propagation speed of the ice formation and water diffusion front and the corresponding freezing depth of concrete samples depending on their capillary-porous structure and initial storage conditions. In general, the studies conducted allowed us to get a more reliable picture of the behaviour of concrete under alternating temperature load than is provided for by current regulatory documents.

Hydro-chemo-mechanical modelling of long-term evolution of bentonite swelling

The swelling properties of compacted bentonite have typically been studied by means of hydro-mechanical models. The question of how these properties are affected by changes in its chemical composition has been given much less attention. However, cation exchange reactions in montmorillonite interlayer or changes in salinity are known to affect the swelling properties of bentonite. In this paper, a hydro-chemo-mechanical (HCM) model is proposed to study the effects of reactive transport processes on the long-term evolution of swelling pressure of compacted bentonite under confined and partially saturated conditions. The HCM model is implemented in iCP, an interface between Comsol Multiphysics and PHREEQC and is calibrated using available experimental data. At the constitutive level, the hydro-mechanical Barcelona Basic model is extended to include the effects of cation exchange reactions between interlayer and bulk water, changes in salinity, and montmorillonite dissolution in highly alkaline environments. The geochemistry of bentonite is based on an advanced reactive transport model that couples solute transport by diffusion and advection with chemical reactions. An application case is presented to demonstrate the main HCM model features and its ability to predict long-term changes in bentonite swelling pressure. The performance of the sealing system for closure of the repository for radioactive waste in France is simulated under unsaturated and isothermal conditions over a period of 50,000 years. The HCM interactions of MX-80 bentonite with other near-field materials such as concrete and claystone are simulated to predict the evolution of the swelling pressure of the seal. The results show the potential of the proposed model for the performance assessment of repository components. Overall, the model predicts limited impact of geochemical alteration on the swelling pressure of the bentonite seals, which is mainly driven by cation exchange reactions between the Na-rich bentonite, the Ca-rich claystone, and the calcium and alkalis from concrete porewater.

Comparison of Diffusion and Migration Coefficients Determined from Tests on Concrete in Prestressed Floor Slabs HC-500

Protective properties of concrete for steel can be assessed with a diffusion coefficient. This method refers to steel exposed to chloride ions present in sea water or deicing agents. However, the aggressive environment with chlorides hinders the determination of diffusion coefficient as they enter into electrostatic interaction with other ions present in concrete pore water, adsorb hardened cement grout on the surface of hydrated minerals, and react with concrete components. But Fick’s laws can be used to express chloride ion flow in concrete regardless of complex physical, chemical and electrostatic processes. Fick’s laws are predominantly used to calculate values of that coefficient values with reference to methods defined by standards AASHTO T 259 and NT BUILD 443. The main disadvantage of such methods is their duration. Therefore, an electric field is used to speed up a flow of chloride ions. On the basis of obtained results, we can either calculate a passed charge or a migration coefficient. The determined coefficient of migration according to NT BUILD 492 characterized chlorides ingress into concrete when exposed to the electric field. But this method did not specify the time, after which the critical value of chloride ions was achieved at the reinforcement. Also, the method described in the standard ASTM C 1202-97 is only useful for comparing protective properties of concrete. However, the migration of chlorides could be analysed with the theoretical model, which was the base to derive the equation of migration. This paper presents experimentally determined averaged results and values of diffusion coefficients determined from migration tests. It also compares results from diffusion tests performed in accordance with standards AASHTO T 259 and NT BUILD443, and results from migration tests conducted in accordance with standards ASTM C 1202-97 and NT BUILD 492.

Experimental Study on the Effect of Temperature on Modal Frequencies of Bridges

This study investigates the relationship between the temperature and the modal frequencies of bridges through a series of model experiments using a concrete continuous beam bridge model and a steel cable-stayed bridge model in a controlled-temperature chamber. The experimental results show that, for a given boundary condition and in the absence of freezing, a change in temperature affects the structural frequencies of the bridge as it alters the elastic modulus of the bridge materials. The structural frequency tends to linearly decrease with increasing temperature and with the decrease in the frequency of steel bridges smaller than that of concrete bridges. For the particular case of wet concrete bridges, the temperature dependencies of modal frequencies vary dramatically near the freezing point, which is attributable to the freeze–thaw process of concrete pore water. The effect of air humidity on structural frequency is less significant than that of temperature when the boundary conditions remain unchanged. Furthermore, temperature changes may alter the boundary conditions of bridges, thereby affecting the structural frequencies.

Coupled THCM model of a heating and hydration concrete-bentonite column test

Radioactive waste disposal in deep geological repositories in clay formations envisage a compacted bentonite engineered barrier and a concrete liner. The alkaline conditions caused by the degradation of concrete could affect the performance of the engineered barrier. The geochemical interactions occurring at the concrete-bentonite interface (B-CI) for the non-isothermal unsaturated conditions prevailing at repository post-closure have been studied by CIEMAT with a heating and hydration concrete-bentonite column test. The column consists of a 3 cm thick concrete sample emplaced on top of a 7.15 cm block of compacted bentonite. The column was hydrated through the concrete at a constant pressure with a synthetic clay porewater while the bottom of the column was heated at 100 °C. Here we report a coupled thermo-hydro-chemical-mechanical (THCM) model of the column test, which lasted 1610 days. The model was solved with a THCM code, INVERSE-FADES-CORE. Experimental observations show calcite and brucite precipitation in the concrete near the hydration boundary, portlandite dissolution and calcite and ettringite precipitation in the concrete, calcite and sepiolite precipitation in the bentonite near the B-CI, calcite dissolution in the bentonite far from the B-CI and gypsum precipitation in the bentonite near the heater. Model results attest that advection is relevant during the first months of the test. Later, solute diffusion becomes the dominant transport mechanism. Calcite and brucite precipitate in the concrete near the hydration boundary because the concentrations of dissolved bicarbonate and magnesium in the hydration water are larger than the initial concentrations in the concrete porewater. Calcite and brucite precipitate in both sides of the B-CI. Sepiolite precipitates in the bentonite near the B-CI. The model predicts portlandite and C1.8SH dissolution in the concrete. Ettringite and C0.8SH precipitate near the hydration boundary while ettringite dissolves in the rest of the concrete at very small rates. The porosity changes occur at the hydration boundary and at both sides of the B-CI due to mineral dissolution/precipitation. The porosity reduces to zero in a 0.03 cm thick zone in the concrete near the B-CI due to brucite and calcite precipitation. The high pH front (pH > 8.5) diffuses from the concrete into the bentonite and penetrates 1 cm at the end of the test after 1610 days. Model results are sensitive to grid size. Mineral precipitation and the thickness of the zone affected by mineral precipitation in the bentonite near the B-CI increase when the grid size increases while pore clogging in the concrete near the B-CI is computed only for grid sizes smaller than 0.018 cm. The non-isothermal conditions play an important role in mineral precipitation. The reduction in porosity in the B-CI for constant temperature is smaller than that of the non-isothermal run. The model reproduces the on-line measured temperature and relative humidity data as well as the water content and porosity data collected at the end of the test. Model results capture the main trends of the mineralogical observations, except for ettringite and CSH phases for which the predicted precipitation is smaller than the observed values. Model results improve when the specific surface of ettringite is increased by a factor of 10.

Effect of Thiosulfate on the SCC Behavior of Carbon Steel Welds Exposed to Concrete Pore Water Under Anoxic Conditions

The Supercontainer (SC) is the reference concept for the post-conditioning of vitrified high-level nuclear waste and spent fuel in Belgium. It comprises a prefabricated concrete buffer that completely surrounds a carbon steel overpack. Welding is being considered as a final closure technique of the carbon steel overpack in order to ensure its water tightness. Welding is known to induce residual stresses near the weld zone, which may lead to an increased susceptibility to stress corrosion cracking (SCC). In this study, slow strain rate tests were conducted to study the SCC behavior of plain and welded P355 QL2 grade carbon steel exposed to an artificial concrete pore water solution that is representative of the SC concrete buffer environment. The tests were performed at 140°C, a constant strain rate of 5 × 10-7 s-1 and at open circuit potential under anoxic conditions. The effect of thiosulfate on the SCC behavior was investigated up to levels of 600 mg/L S2O32-.

Investigation of chabazitic materials as Cs-137 sorbents from cementitious aqueous solutions

The ability of a chabazite-bearing tuff (AT), a synthetic chabazite (SYN) and pure natural chabazite crystals (CHA) to sorb cesium (CCs: 10−9 - 10−2 M) from young concrete pore water (YCW), an aqueous medium that can potentially leach from cement-based barriers of radioactive waste disposal facilities, was investigated using a batch technique and 137CsCl-spiked solutions. The sorbents were mineralogically characterized prior and after the sorption tests, whereas their uptake ability was determined by the ammonium acetate saturation (AMAS) method. Two series of experiments were performed using sorbate solutions in pH∼13 and pH∼7 YCW (contact time: 14 days and 100 days). The Cs-uptake by the zeolites was determined by counting the 661.6 keV 137Cs γ-rays in the liquid phase. SYN presented the highest Cs-uptake ability followed by CHA and AT. The Cs-uptake, which remained constant between 14 and 100 days, depended on the zeolite content of the sorbents and the Cs-concentration of the solutions. The zeolites remained stable in the YCW environment for the total duration of the experiment. Kinetic experiments, performed for AT at 23, 35 and 50 °C using a 10−3 M Cs-solution in pH∼13 YCW spiked with 137Cs, showed that the equilibrium was established, for all temperatures, in less than 30 min. Cs-leaching tests (duration: 14 days and 100 days) performed using pH ∼13 YCW as eluent, indicated that AT was the most sensitive to leaching losing ca. 60% of the sorbed Cs in less than 10 min, whereas SYN and CHA ca. 30%. No further leaching was observed at prolonged contact of the Cs-loaded zeolites with YCW.

Potentiometric Response of Ag/AgCl Chloride Sensors in Model Alkaline Medium

The stability and reproducibility of an Ag/AgCl sensors’ response in an alkaline medium are important for the application of these sensors in cementitious materials. The sensors’ response, or their open circuit potential (OCP), reflects a dynamic equilibrium at the sensor/environment interface. The OCP response in an alkaline medium is affected by the presence of hydroxide ions. The interference of hydroxide ions leads to inaccuracies or a delay in the sensors’ response to a certain chloride content. In this article, the potentiometric response (or OCP evolution) of the chloride sensors is measured in model solutions, resembling the concrete pore water. The scatter of the sensors’ OCP is discussed with respect to the interference of hydroxide ions at varying chloride concentration in the medium. The deviation of the sensor’s response from its ideal performance (determined by the Nernst law) is attributed to dechlorination of the AgCl layer and the formation of Ag2O on the sensor’s surface. Results from the surface XPS analysis of the AgCl layer before and after treatment in alkaline medium confirm these observations in view of chemical transformation of AgCl to Ag2O.

Enhanced bamboo composite with protective coating for structural concrete application

Potential application of newly developed bamboo composite material as structural reinforcement called forth for durability test and bond strength examination. Firstly, durability of bamboo composite material and effectiveness of protective epoxy coating were evaluated by subjecting samples to various corrosive environments normally encountered during the life span of construction materials. At accelerated conditions, samples were immersed in water, simulated acidic rain solution and simulated concrete pore water solution for 28 days. Tensile tests and microstructural analysis were conducted to investigate the impact of different corrosive environments on the bamboo composite material’s behavior. The results revealed that the application of epoxy coating successfully protected bamboo composite material’s integrity without substantially affecting its mechanical capacity, particularly in acidic environment. Secondly, bond strength between bamboo composite material and concrete was investigated through pull-out tests. The epoxy coating improved the bond strength, especially with addition of sand particles. The findings of this study suggest that epoxy coating can be an effective approach to simultaneously enhance the bamboo composite material’s resistance towards acid attack and improve its bond strength with concrete for concrete reinforcement application.

Carbon Steel Corrosion in Simulated Anoxic Concrete Pore Water for Nuclear Waste Disposal Application

Carbon steel is a potential canister material for high-level waste disposal in underground geologic repository systems where reducing conditions dominate after the thermal period. For example, the super container concept in the proposed Boom Clay repository concept in Belgium comprises a carbon steel overpack containing the waste and an outer stainless steel liner forming the boundary of an annular region containing a cementitious material. The outer surface of the carbon steel overpack would be in contact with concrete pore water with pH near 12.5, expected to persist for thousands of years. This study investigated carbon steel passivity, corrosion rate, repassivation, hydrogen generation, and hydrogen induced cracking tendency in simulated concrete pore water under anoxic conditions, and the effects of possible anions in the pore water such as Cl−, , and S2−. Carbon steel maintained its passivity at 50°C and 80°C up to a test period of 6 months and passive corrosion rates were mostly in the range of 0.1...

Corrosion issues of carbon steel radioactive waste packages exposed to cementitious materials with respect to the Belgian supercontainer concept

ABSTRACTThe supercontainer is the reference concept for the post-conditioning of vitrified high-level radioactive waste and spent fuel in Belgium. It comprises a prefabricated concrete buffer that completely surrounds a carbon steel overpack. In this highly alkaline environment (pH ∼13.6) and under normal conditions (i.e. without the ingress of aggressive species), the carbon steel overpack will be protected by a passive oxide film, which is expected to result in very low uniform corrosion rates. Considering the long timescales applicable to waste disposal, determining accurate and reliable estimates of the uniform corrosion rate under anoxic conditions forms a very important part of the safety and feasibility strategy. On the other hand, the occurrence of localised forms of corrosion cannot be neglected and, therefore, it is also crucial to demonstrate that no other form of corrosion apart from uniform corrosion can take place. This paper gives an overview of the status of the research into the uniform corrosion, pitting corrosion and stress corrosion cracking behaviour of P355 QL2 grade carbon steel exposed to an artificial concrete pore water solution.This paper is part of a supplement on the 6th International Workshop on Long-Term Prediction of Corrosion Damage in Nuclear Waste Systems.