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The diffusion potentials can cause significant errors in corrosion-related investigations of reinforced concrete structures (half-cell potential mapping, potentiometric sensors). Therefore, an improved understanding of the diffusion potentials in cement-based materials is needed. This study investigates the permselective behavior and its implication for the arising diffusion potentials. A diffusion cell is used to study the diffusion potentials in hardened cement pastes with imposed NaCl gradients. The cement pastes consist of ordinary Portland cement (OPC) and blast furnace cement (BFC) with water-cement ratios of 0.30–0.70. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is used to determine the concentration profiles of Cl, Na, K and Ca in the cement pastes with a high spatial resolution (100 µm). For the BFC pastes, considerable differences in the Cl− and Na+ mobilities are found, indicating their permselective behavior. Despite the permselective behavior, the measured diffusion potentials are small (− 6 to + 3 mV) for all investigated cement pastes due to the high pH levels (13–14) in the pore solutions. However, when using the diffusion cell, the pH differences interfere with the measured diffusion potentials. The interfering pH differences need to be considered for an accurate measurement of the diffusion potentials in cement pastes., Materials and Structures, 56 (5), ISSN:1359-5997, ISSN:0025-5432, ISSN:1871-6873

The critical chloride content C-crit is an indicator of the corrosion resistance of reinforcing steels in concrete. In this article, several experimental methods for determining the critical chloride content C-crit of mild and alloyed (12% Cr) steel in cementitious materials are compared. The methods used include accelerated polarization tests and tests employing more natural (unpolarized) conditions in which chloride ingress occurs by diffusion and capillary uptake. The advantages and disadvantages of the methods are discussed, in particular, against the objective of reaching a compromise between applicability to practice and feasibility in laboratory testing., Materials and Corrosion, 73 (3), ISSN:0947-5117, ISSN:0043-2822, ISSN:1521-4176

Corrosion assessment of reinforced concrete (RC) structures with fusion-bonded-epoxy (FBE)-coated steel rebars is a challenge because the common inspection methods and data cannot be applied or interpreted in the same way as that for the systems with uncoated rebars. If corrosion detection tools based on techniques such as half-cell potential (HCP), linear polarization resistance (LPR), or electrochemical impedance spectroscopy (EIS) are used for the assessment of systems with FBE-coated steel rebars without considering the difference in the electrochemical conditions between coated and uncoated systems, then the interpretation can result in the inability to detect ongoing corrosion. Therefore, the objective of this paper is to examine the suitability of these inspection methods and data to be applied to the RC systems with FBE-coated steel rebars. For this, the suitability of test methods on HCP, LPR, and EIS for assessing corrosion conditions of RC structures was assessed using laboratory specimens and field structures. Field investigation using HCP shows that the HCP could not detect corrosion of FBE-coated steel rebars unless the coating was severely disbonded due to corrosion of steel rebars. Also, the suitability of test methods on HCP, LPR, and EIS was assessed by additional laboratory specimens. Although complex, only the EIS technique could reliably detect the corrosion conditions of the FBE-coated steel rebars embedded in concrete. Therefore, a way forward to assess RC structures using the EIS technique is proposed.

Cracks in concrete structures can serve as pathways for aggressive chemical substances that can lead to a progressive deterioration of the cement stone as well as of the reinforcement, affecting the load capacity, service life and useability of concrete structures. However, concrete and reinforced concrete exhibit an intrinsic ability to heal cracks, defined as autogenous self-healing. This effect includes the precipitation of calcium carbonate in the presence of water and CO2 and is accompanied by continued hydration, swelling and mechanical blocking of the crack pathway. Experiments led to the inclusion of crack healing by autogenous self-healing in Eurocode 1992-3 for water retaining concrete structures. However, despite code restrictions, autogenous self-healing of concrete shows limited effectiveness in practice. This indicates the need for further research to provide engineers with reliable design rules. Therefore, this study aims for giving a broad literature review on the state-of-the-art knowledge on autogenous self-healing, the boundary conditions, consensus and controversy of processes and factors influencing the efficiency of autogenous self-healing. Regarding the transferability of laboratory results to real concrete constructions, materials, crack initiation techniques, experimental concepts and methods for assessing the effectiveness of autogenous self-healing are discussed and recommendations for future experiments are set.

Fusion-bonded-epoxy (FBE)-coated steel rebars have been used in many concrete structures in anticipation of better corrosion resistance. However, due to premature corrosion observed, FBE-coated reb...

Autogenous self-healing of water retaining concrete structures is included in Eurocode 1992-3 as a possibility to heal cracks up to a width of 200 μm without additional repair. In this self-healing scenario water flow through a crack should result in a progressive closure of the fracture, mainly due to CaCO3 precipitation, when certain hydraulic gradients are met, the pH of the water is > 5.5 and the concentration of CO2 in the water remains < 40 mg*L-1. The material composition is not further restricted by the regulation. However, despite standardization, the healing effect seems to be random in practice, which requires further research, while experiments aimed at quantifying autogenous self-healing are expensive and time-consuming. Thermodynamic models could support in estimating the effect of different environments such as groundwater or seawater exposure on autogenous self-healing. Moreover, adjusting the water chemistry according to the conditions of different construction sites and changing the material design could easily be considered. In this study thermodynamic models of a hydrated CEM I 52.5 R paste that is exposed to either simulated groundwater or seawater are discussed concerning the influence on autogenous self-healing and compared to experimental and literature data.

Stainless steel is a possible measure for increasing the service life of reinforced concrete structures exposed to chlorides. For the prediction of service life it is crucial to quantify the corrosion resistance of the material used by determining the chloride threshold at the steel concrete interface inducing corrosion at the rebar. However, currently the corrosion resistance of stainless steel is expressed by its pitting resistance equivalent number (PREN) which considers only the content of chromium, molybdenum and nickel along with certain factors. The higher the PREN-value, the more corrosion resistant the steel. But this PREN-value cannot be transferred into a chloride threshold concentration. Therefore, this paper presents a test method, the so called “ECISS”-test (ECISS = European Commission for International Steel Standardization), which enables the evaluation of the chloride threshold of stainless steel. The focus is on the performance of this test with respect to its limits and opportunities. Test results of different types of stainless steels are included and discussed. The benefit of stainless steel with respect to the service life of reinforced concrete structures is highlighted.

Often the mere mention of the word “Sustainability” leads to the reflection of the effect of our actions on environment and future generations. Especially the application of reinforced concrete as the most used construction material has a huge impact on a society being sustainable. Thus, the construction industry focuses on the design of environmentally- and resource-friendly buildings. However, due to our aging infrastructure and expected high demand of maintenance and repair in future, a further look on the sustainability of different repair measures for reinforced concrete structures has been neglected in the past. This paper presents a comparative case study of the life-cycle analysis of two different repair measures for reinforced concrete affected by chloride-induced corrosion. The selected repair measures – removal of the chloride-contaminated concrete and cathodic protection – are the most common repair measures in Germany. In future way concrete repair measure could be selected not only by the costs but as well by their environmental impact. This paper provides first information to achieve this target.

Reinforced concrete (RC) is the most used construction material for infrastructure due to its strength and durability. However, under chloride exposure, often the RC structures do not achieve their designed service life. Therefore, premature repairs or even replacement of components is required, hence increasing the environmental impacts and economic costs over the entire service life. This study evaluates the sustainability of low-clinker cements as a corrosion prevention measure in reinforced concrete under several chloride exposures conditions. Through a life cycle assessment (LCA), the environmental impacts of a RC generic element are evaluated, considering three alternatives for low-clinker cement and ordinary Portland cement as reference. The materials production and use service are considered in the LCA. The service phase includes the repair activities necessary to keep a defined level of serviceability given the steel corrosion due to chloride ingress. The number of repairs is determined on a probabilistic durability assessment. The results showed that the durability of the reinforced element plays a major role in the overall environmental impacts. Furthermore, low-clinker binders have a positive environmental impact in the sustainability of reinforced concrete structures.

Impact of a concrete coating on the reinforcement corrosion in cracked concrete Cracks in reinforced concrete structures exposed to chlorides can significantly impair the durability. Cracks are a fast pathway for chlorides and corrosion initiation of the reinforcement is more likely. Relevant standards [1, 2] require additional measures to prevent chloride ingress into structures exposed to chlorides such as parking decks. Additional design principles to ensure the durability of parking decks are given by the German Society for Concrete and Construction Technology (DBV) [3]. One principle consists of the application of a crack bridging concrete coating to prevent further chloride and moisture supply once early cracking is completed even though chlorides are already present in the crack. This recommendation is in line with the repair principle W-Cl according to RL SIB [4] and the procedure 8.3 DIN EN 1504-9 [5] respectively with the objective to increase the concrete resistivity. In an extensive experimental study it can be shown that concrete coating prevents corrosion and can even stop macro cell corrosion successfully in bending cracks with short-term chloride exposure. The repassivation is based on the increase of the anodic polarization resistance due to oxide layer formation and/or limited supply of chlorides. The concrete resistivity increases as well because of ongoing drying of the concrete but its effect on the macro-cell activity is negligible. It remains to be determined which amount of chlorides can be left in the concrete to exclude on-going reinforcement corrosion reliably.

Chloride ingress in cracked concrete leads to rapid corrosion of embedded steel reinforcement and a decrease of the expected service life. Corrosion monitoring experiments showed that a 300 μm wide crack caused initiation of corrosion of a rebar (O 10 mm) with a concrete cover of 26 mm within three weeks of cyclic exposure to a 33 g/l NaCl solution. After a period of unstable corrosion activity during the first 20 weeks of exposure, corrosion propagated further at a relatively high rate (0.345 to 0.718 mm³/week). Application of a theoretical pitting model revealed that a reduction of about 50% of the rebar cross-section would occur after a period of 9 to 20 years of continuous cyclic exposure to chlorides. To avoid such rapid degradation, the use of self-healing concrete can be proposed. Introduction of macro-encapsulated polyurethane into the concrete matrix, will lead to the formation of a (partial) barrier against ingress of chlorides at the moment cracks appear. Corrosion monitoring experiments showed that the autonomous crack healing could not always prevent corrosion initiation, but caused an important reduction of the corrosion rate during the 44 weeks exposure period. The mean rate of volumetric loss of steel amounted to 0.042 mm³/week, about 15 times lower than for the untreated cracked samples. The rebars also showed no or very limited signs of corrosion after visual inspection. The simplified pitting model indicated that a 50% reduction in steel cross-section would take more than 5 times longer for samples with self-healing properties versus ordinary cracked samples.

Infrastructural buildings are subject to a high risk of reinforcement corrosion resulting from de- icing salts. A lot of effort is put in the design of these buildings in order to minimize this risk and ensure the durability during their service life. However, the evaluation of the effectiveness of these measures as well as the resulting corrosion state is an essential but critical part in the assessment of the structural condition. Therefore a versatile corrosion monitoring system was developed, which can be retrofitted in structures which are subject to a certain corrosion risk. In a first case study this monitoring system was installed in two parking structures in southern Germany which were subject to cracks in the concrete cover, combined with a chloride exposure during winter periods. All basic electrochemical parameters of reinforcement corrosion could be measured allowing for an evaluation of the corrosion development before and after the coating measure. The principle of the monitoring system proved to be an effective tool and can be used in a wide range of structures (bridges, parking garages etc.).

Epoxy-coated reinforcement (ECR) as a means of protection against chloride-induced corrosion of steel in concrete is used in only a few countries due to doubts concerning its effectiveness. A common misconception is that possible defects in the coating are particularly weak points as these might favour high local corrosion rates and thus loss of steel cross-section. This work discusses why a certain number of small defects can be tolerated. It is argued that prolongation of the initiation phase is caused by a higher critical chloride content compared with uncoated steel due to the “size effect”. Additionally, the propagation phase for ECR is likely to be extended due to the severely restricted cathodic area that limits the corrosion rate. This paper presents experimental and numerical tests to verify these assumptions.

Die Detektion von korrodierenden Bereichen in Stahlbetonbauwerken ist ein wesentlicher Schritt fur die Zustandserfassung und die Planung von Instandsetzungsmasnamen. Als etabliertes Messverfahren steht dafur die Potentialfeldmessung zur Verfugung. Obwohl dieses Verfahren schon seit Jahren eingesetzt wird und in verschiedenen Richtlinien und Merkblattern Eingang gefunden hat, gibt es immer noch offene Fragen zur Oberflachenvorbehandlung, zum geeigneten Messzeitpunkt bei frei bewitterten Bauteilen und zum optimalen Messraster. Diese Fragen werden anhand von Labormessungen und praxisnahen Feldmessungen qualitativ untersucht. Fur die praxisnahen Feldmessungen wurden Potentialfelder an 40 Jahre alten, naturlich korrodierten Stahlbetonrandbalken vom Olympiastadion in Munchen bei unterschiedlichen Oberflachenvorbehandlungen, nach verschiedenen Wetterszenarien und Messrastervariationen ausgewertet. Study of potential mapping at 40 year old reinforced elements from the Olympic stadium in Munich – Influence of concrete resistivity and grid size An essential part of the inspection and repair planning of reinforced concrete structures is the detection of corroding areas. Potential mapping is a widely used and established procedure to do this. But there are still some open questions concerning this measurement procedure. Which is the proper pre-wetting condition or which is the best time to measure when the structural element is exposed to weather conditions? Which is the optimal grid size? Investigations are made with a laboratory and practical test set up. For the practical test set up 40 year old, naturally corroded reinforced segments from the Olympic stadium in Munich are available and potential measurements under different condition were analyzed qualitatively.

Die Potentialfeldmessung ist ein Standardverfahren zur Zustandserfassung von Stahlbetonbauwerken. Sie dient der zerstorungsfreien Detektion von aktiv korrodierenden Bereichen. Die Aussagegenauigkeit der Potentialfeldmessung ist von groser wirtschaftlicher Bedeutung, da deren Messergebnisse eine wichtige Entscheidungsgrundlage fur die Erarbeitung von Instandsetzungsmasnahmen bilden. Zur Ermittlung der Aussagegenauigkeit der Potentialfeldmessung wird ein numerisches Verfahren vorgestellt. Die wichtigsten Einflussgrosen auf die Potentialfeldmessung wie Anodengrose, Elektrolytwiderstand und Messraster wurden im Hinblick auf die Aussagegenauigkeit ausgewertet. Potential mapping and its probability of detection Potential mapping is a feasible non-destructive method to detect actively corroding areas in reinforced concrete structures. The probability of detection of potential mapping has a high economical impact, because the test results of this method are the basis for maintenance and repair schedules. A numerical approach is presented to evaluate the probability of detection. The probability of detection of potential mapping has been evaluated regarding the most influencing parameters like anode area, concrete resistivity and grid size.