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An important input parameter for numerical models that simulate cracking of the concrete cover due to reinforcement corrosion is the Elastic modulus of corrosion product (Ecp). Despite its relevance, Ecp is subject of significant variations according to the values reported in the literature, which vary from less than 100 MPa up to 360 GPa. Furthermore, Ecp values proposed in most of the present literature are representative of the corrosion product generated by anodic accelerated corrosion or extracted from the steel/concrete interface (SCI), which might differ from that formed in real corroding structures. Therefore, this study aims to investigate the Elastic modulus of naturally-generated corrosion product present at the SCI through nano-indentation conducted on six reinforced concrete polished sections. The polished sections were obtained from six 20-year-old reinforced concrete prisms cast with different cement type (CEM I, CEM II/B-V, CEM III/B, CEM V/A), same water/binder ratio (0.55) and which were previously exposed to NaCl solution wet/dry cycles. This study revealed that the range of Ecp did not considerably vary between corrosion products formed in different concrete mixes. However, corrosion product was microscopically found to consist of overlapping bands with different Ecp, varying for up to around 70 GPa between each other. Through Environmental Scanning-Electron Microscopy (ESEM) and Energy Dispersive Xray Spectrometry (EDS) analysis of the indented locations, it was found that Ecp is highly dependent on the presence of interfacial cracks and inversely proportional to the concentration of Si and Ca, representative for corrosion product mixed with the surrounding concrete. Furthermore, higher concentration of Fe leads to higher Ecp. Based on this study, an average range of values for Ecp between 80-100 GPa can be suggested for use in numerical models for corrosion induced cracking, regardless of cement type of the structure under investigation.

The steel–concrete interface (SCI) is known to influence corrosion of steel in concrete. However, due to the numerous factors affecting the SCI—including steel properties, concrete properties, execution, and exposure conditions—it remains unclear which factors have the most dominant impact on the susceptibility of reinforced concrete to corrosion. In this literature review, prepared by members of RILEM technical committee 262-SCI, an attempt is made to elucidate the effect of numerous SCI characteristics on chloride-induced corrosion initiation of steel in concrete. We use a method to quantify and normalize the effect of individual SCI characteristics based on different literature results, which allows comparing them in a comprehensive context. It is found that the different SCI characteristics have received highly unbalanced research attention. Parameters such as w/b ratio and cement type have been studied most extensively. Interestingly, however, literature consistently indicates that those parameters have merely a moderate effect on the corrosion susceptibility of steel in concrete. Considerably more pronounced effects were identified for (1) steel properties, including metallurgy, presence of mill scale or rust layers, and surface roughness, and (2) the moisture state. Unfortunately, however, these aspects have received comparatively little research attention. Due to their apparently strong influence, future corrosion studies as well as developments towards predicting corrosion initiation in concrete would benefit from considering those aspects. Particularly the working mechanisms related to the moisture conditions in microscopic and macroscopic voids at the SCI is complex and presents major opportunities for further research in corrosion of steel in concrete.

Owners of concrete structures would benefit from knowing when to expect corrosion initiation in a particular structure. Presently, no accepted procedures for testing existing structures for the remaining time to corrosion initiation are available. This paper proposes such a procedure, based on our experience and additional considerations. From about 20 years age, existing structures contain the concrete’s response to actual environmental loads, e.g. chloride ingress profiles. By measuring the actual cover depth, taking chloride profiles, assuming a few parameters and a simple model, the expected time to corrosion initiation for a particular test area can be predicted. Numbers of cores and samples per core are given. Uncertainties can be taken into account by applying a calculatory reduction of the cover depth. Results of at least six cores per test area are classified and suggested interpretations are given. Because of large variability, the results are classified in three ranges of time to corrosion initiation: five years or less, five to fifteen years, or more than 15 years. The procedure has been approved by the relevant national Standards committees and is issued early 2018. It was applied to a field case and the obtained results are discussed.

In der aktuellen Fassung der Betonnorm EN 206 wird ein deskriptives Konzept fr die Dauerhaftigkeit des Betons ver-wendet, wobei der Nachweis der Dauerhaftigkeit liber die Einhaltung der Grenzwerte des Regelwerks bezgIich Beton-eigenschaften und Betonzusammensetzung gefiihrt wird. Dabei wird aber der Einfluss der jeweiligen Zementart oder des Betonzusatzstoffs nicht ausreichend bercksichtigt. Die Weiterentwicklung der zuknftigen euroOischen Betonnorm EN 206 sieht unter anderem den Einsatz leistungsbezogener Entwurfsverfahren (Performancekonzept) fr Beton vor, bei dem dies und auch die zeitliche Entwicklung von Einwirkungen und Widerstinden besser bercksichtigt werden. Der Widerstand des Betons gegen das Eindringen von Chloridionen ist dabei eine der wichtigsten Eigenschaften des Betons mit hoher Relevanz fiir die Dauerhaftigkeit. Die Auswahl der Betonausgangsstoffe und die Festlegung der Betonzusammen-setzung beeinflussen den Chlorideindringwiderstand von Beton wesentlich. Eine der betontechnologischen MaBnahmen zur Erhijohung des Chlorideindringwiderstands von Beton ist der Einsatz von Flugasche und Hilttensandmehl als Bestand-teil des Zements oder als Betonzusatzstoff. Die Prfung und die Bewertung des Chlorideindringwiderstands sind in Europa noch nicht endgultig geregelt. In den Niederlanden liegen bereits langjahrige Erfahrungen mit dem Einsatz von Betonen mit hohem Chlorideindringwiderstand und Priffergebnisse vor, die eine Bewertung bezglich der Abh.ngigkeit von der Betonzusammensetzung als auch vom Alter des Betons zulassen

In the Netherlands civil engineering structures, such as overpasses, bridges and tunnels are generally built using blast furnace slag cement (BFSC, CEM III/B) concrete, because of its high resistance against chloride penetration. Although the Dutch experience regarding durability performance of BFSC concrete has been remarkably good, its resistance to carbonation is known to be sensitive, especially when the used slag percentage is high. In a field investigation on a highway overpass damage was found in sheltered elements such as abutments and intermediate supports, which was attributed to chloride induced corrosion enhanced by carbonation that occurred prior to the chloride exposure. Many structures built using BFSC could be prone to this mechanism, i.e. carbonation enhanced chloride induced corrosion, negatively affecting their durability. Focus of the research was given on the influence of carbonation on the chloride penetration resistance of BFSC mortars with varying slag content. In light of the characteristics from the overpass case, it was assumed that first there is a period of carbonation during sheltered exposure, and subsequently joint leakage causes exposure to chlorides. In order to identify the influence of slag content on carbonation, chloride penetration resistance and their coupled effect, mortars with twelve cement blends in a range of 0-70% slag were evaluated based on chloride migration coefficient, accelerated carbonation and electrical resistivity. This study shows that carbonation of BFSC mortars increases the porosity, consequently decreasing the chloride penetration resistance. Binders with 50% or more slag were found to have a significantly lower resistance after carbonation. Consequently, the chloride penetration resistance of a given concrete cover strongly depends on the duration of carbonation and the resulting carbonation depth, hence influencing its lifespan. The service life was estimated using a simplified model for the chloride penetration time of a combined carbonated and uncarbonated layer. It was found that mortar with a slag content between 35 and 50% that was carbonated before chloride exposure show the lowest influence of carbonation on the chloride penetration resistance. © Springer International Publishing AG 2018. Bam; Cement and Beton Centrum; et al.; Rijkswaterstaat - Ministry of Infrastructure and the Environment; Van Hattum en Blankevoort; VolkerInfra

Many repairs of chloride induced corrosion in practice fail within 10 years due to chloride remaining after cleaning the steel, causing corrosion re-activation. An improvement of conventional repair was invented, Electro Active Repair, that electrochemically removes chlorides. After concrete removal, a temporary electrolyte and anode are installed and direct current is applied for 24 hours. Subsequently repair is as usual. Patents have been applied. Laboratory testing confirmed the principle. A cementitious material was placed between NaOH and FeCl2 solutions. More than 90% of the chloride was removed from the catholyte (FeCl2) in 20 hours at 8 A/m2 and the pH increased from 3 to 12. This will suppress re-activation of corrosion and improve the durability of the repair. The method fits in the conventional repair process. The additional cost is moderate. Applying the invention increases repair life and reduces life cycle cost of corrosion affected structures.

Testing for the chloride threshold (also called critical chloride content) for corrosion initiation of steel in concrete has been found difficult and, at best, time consuming. Nevertheless, the chloride threshold is an important parameter in service life design of new structures and for evaluation of the remaining service life of existing structures. This paper reports on an accelerated test on mortar specimens that produces results within one week to a few weeks. It is based on accelerating chloride penetration by a mild electrical field while the steel potential is monitored. Upon corrosion initiation, specimens are sampled to obtain the chloride content that initiates corrosion. Results are reported of testing in CEM I (OPC) mortar on multiple specimens. Results for reference mortar are compared to specimens with application of a hydrophobic surface treatment. The results show that in reference CEM I mortar values for the critical threshold were obtained that agree well with previous experiments using the same method. This is taken as a validation of the method. The method is thought to be suitable for comparative chloride threshold studies of different binders, without or with corrosion inhibiting additions. Results for mortar with surface applied hydrophobic treatment, however, are unexpectedly low, which is taken to suggest that the method is not suitable for (e.g. surface treated) material with inhomogeneous electrolytic conduction. © Springer International Publishing AG 2018. Bam; Cement and Beton Centrum; et al.; Rijkswaterstaat - Ministry of Infrastructure and the Environment; Van Hattum en Blankevoort; VolkerInfra

In theorie naderen veel bruggen en viaducten hun einde levensduur, maar de soep wordt niet zo heet gegeten als zij wordt opge-diend. Veel kunstwerken bezitten verborgen krachten. Toch is het nodig alle over-spanningen goed in kaart te brengen en kennis over dit onderwerp met elkaar te delen en/of op te bouwen

Asset managers would benefit from knowing when to expect corrosion initiation in a particular reinforced concrete structure. However, accepted approaches to test existing structures for the remaining time to corrosion initiation are lacking. This paper proposes such an approach, based on experience in the field and additional considerations. From say 20 years age, existing structures embody the concrete's response to actual environmental loads, e.g. in chloride profiles. Based on measuring the actual cover depth, taking (at least six) chloride profiles, some assumed parameters and a simple model, the expected time to corrosion initiation for a particular test area can be predicted. Sampling frequencies are given. Uncertainties can be taken into account by applying a safety margin to the cover depth. Results of at least six tests are classified and suggestions for interpretation are given. Because the accuracy is limited, the results are classified in three broad ranges: 5 years or less, 5 to 15 years, or more than 15 years. The procedure is applied to a field case and results are discussed. © Springer International Publishing AG 2018. Bam; Cement and Beton Centrum; et al.; Rijkswaterstaat - Ministry of Infrastructure and the Environment; Van Hattum en Blankevoort; VolkerInfra

Blast furnace slag cement (BFSC) has been used in reinforced concrete structures in marine and road environment in The Netherlands for nearly a century. Experience is good and long service lives can be obtained. In Norway experience with BFSC is scarce. In The Netherlands, a high resistance against chloride penetration and a high electrical resistivity, was demonstrated both in the field and in the laboratory for CEM III/B with 65-75% of slag by mass of binder. Such a cement is not readily available on the Norwegian market. The introduction of CEM III/A with c. 50% slag is anticipated. An experimental program was carried out to study the properties of five mortar mixes made with: CEM III/B (two brands); a CEM III/A (with c. 50% slag) with silica fume; and a CEM I and a CEM II/A-V (fly ash cement), both with silica fume. Rapid Chloride Migration (RCM) and electrical resistivity were tested at ages between two days and one year. RCM values showed consistent decrease and resistivity showed consistent increase between two days and one year. The program is intended to collect data up to three years age. The ultimate goal is to provide a basis for evaluating the use of slag cement in Norway for durable concrete structures. The paper reports the results and discusses the preliminary conclusions.

Chloride induced reinforcement corrosion is the most common degradation mechanisms for reinforced concrete structures. The service life of concrete structures is normally predicted by estimating the rate of chloride ingress and the necessary time to initiate reinforcement corrosion. Normally, chloride ingress is modeled as a diffusive process in which concrete is considered as a semi-infinite continuous medium. This modelling approach disregards the influence of cracks on the rate of chloride ingress in concrete. However, experimental studies have shown that the influence of cracks on chloride ingress is significant and cannot be neglected. In practice, cracks in concrete may originate due to different mechanisms. Recommendations on crack control in flexural members consider cracks in the range between 0.15 mm (0.006 in.) and 0.3 mm (0.011 in.) to be permissible in deicing and/or seawater exposure; with the same limit for both exposure classes in Europe. The influence of cracks on service life prediction remains to be clarified. This paper presents describes a conceptual approach for incorporating the effect of flexural cracks on the calculation of the time-tocorrosion initiation of steel reinforcement due to chloride-ingress. The proposed approach consists of applying a correction factor to the chloride diffusion coefficient, which is dependent on the surface crack width.

Maintenance costs of reinforced concrete infrastructure (bridges, tunnels, harbours, parking

Maintenance costs of reinforced concrete infrastructure (bridges, tunnels, harbours, parking structures) are increasing due to aging of structures under aggressive exposure. Corrosion of reinforcement due to chloride ingress is the main problem for existing structures in marine and de-icing salt environments. Corrosion cannot be ruled out completely for new infrastructure, even with today's emphasis on design for long service life (e.g. 100 years), a.o. due to local effects such as leakage of joints; consequently, repairs may be necessary. This study reports on total life cost calculations for various options to prevent or remediate corrosion damage in an example bridge which is exposed to de-icing salts, locally aggravated by leakage of expansion joints. Scenarios were developed to predict - the occurrence of corrosion damage in the joint areas, - total life cycle cost (LCC) effects of using stainless steel reinforcement, (repeated) hydrophobic treatment and cathodic prevention in the joint areas, - cost effects of conventional concrete repair and cathodic protection in the joint areas, depending on the working life of these corrective measures. Summarising the preliminary results, using stainless steel reinforcement and (repeated) hydrophobic treatment of concrete in the endangered areas is surprisingly economic. Furthermore, the working life of conventional repairs and cathodic protection are major parameters affecting the total life costs. A simple tool was developed for predicting the total life costs depending on working life and costs of various preventive and corrective measures.

This paper, describes experiments that form the basis of an invention that aims

Die oberste niederländische Straßen- und Wasserbaubehörde (Rijkswaterstaat) hat im Hinblick auf die langfristige Instandhaltung ihrer Infrastruktureinrichtungen über 1500 Endverankerungsbereiche von Spannbetonbrückenträgern instandgesetzt und einer kathodischen Korrosionsschutzbehandlung (KKS) unterzogen. Die Endbereiche wiesen mäßige bis starke Schäden durch Bewehrungskorrosion auf. Verursacht wurde die Korrosion durch Chloride, die über undichte Fugen eingedrungen waren. Durch den kathodischen Korrosionsschutz konnte der fortschreitende Korrosionsprozess unterbunden werden. Damit wurde das Risiko einer weiteren Zustandsverschlechterung der Spannbetonträger und eines möglichen Bruchs der Spannglieder auf ein Mindestmaß reduziert. Letztlich konnte die Nutzungsdauer von 30 betrachteten Brücken um mehr als 20 Jahre verlängert werden. Der vorliegende Beitrag skizziert die gewählte Herangehensweise. Application of cathodic protection on 30 concrete bridges with pre-stressing steel: remaining service life extended with more than 20 years In view of long term maintenance of its infrastructure facilities the Dutch Highway Administration (Rijkswaterstaat) has repaired over 1.500 heads of prestressed beams and provided them with cathodic protection (CP). The heads of these beams showed moderate to severe damage due to reinforcement corrosion caused by the penetration of chlorides from leaking joints, which required adequate intervention on the short term. By means of cathodic protection the corrosion process has been halted, so that the risk of further degradation of the beams and possible failure of the pre-stressing steel tendons has been minimized. In addition, the concrete repairs in the chloride contaminated parts of the beams will be durable. Copyright © 2015 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin.

In Nederland bestaat al ruim 25 jaar ervaring met kathodische bescherming (KR) van wa pening in beton. Over de jaren is gebleken dat dit een betrouwbare methode is die corrosie stopt, mits voldoende aandacht aan ontwerp, uitvoering en onderhoud wordt besteed. Re cent is KR toegepast op ruim 30 snelwegviaducten. Aan de techniek van KR en de toepas sing op voorgespannen liggers wordt elders in dit nummer aandacht besteed. Hier beperk ik me tot de geschiedenis van de methode en wat overwegingen hij het liggerkoppenproject

Alkali-Silica Reaction (ASR) is a durability problem that affects numerous concrete structures woridwide. As the reaction progresses. it might lead to deleterious expansion and cracking. The addition of lithium into fresh concrete is already acknowledged as a preventive method. In existing structures, however, lithium would need to be driven into the concrete and the most effective way is through ionic migration. For migration to occur in reinforced concrete, power is supplied between an external electrode and the rebar. If the reinforcement is the cathode, it attracts positive ions, such as lithium ions. Several studies have been conducted on the use of lithium migration as a treatment for ASR. Nevertheless, so far, there is no agreement on the conclusions. It is necessary to better understand this process order to develop a possible treatment against ASR. In this work, a preliminary investigation on lithium migration into mortar specimens with embedded cathode is presented.

This paper reviews 25 years of experience with cathodic protection of steel in concrete in The Netherlands. Three phases have passed from the late 1980s until present: pioneering, development and maturity. In the first period CP was mainly applied to precast elements corroding due to mixed in chlorides. The parties involved worked together to draw up a Technical Guideline. In the second period, application to bridges was developed, including post-tensioned structures, which was then innovative. Furthermore, galvanic anode systems were introduced. In the third period, CP became a fully accepted method of securing safety and serviceability. The annual number of projects increases considerably and increased competition has reduced prices. Renewed collaboration led to a database that allowed analysis of various aspects of CP system working life; and to new developments in modelling. Major successes and lessons learned will be presented. Technical and non-technical developments are highlighted and some recent findings on long term behaviour are discussed

Alkali-silica reaction (ASR) is one of the major deterioration mechanisms that affect numerous concrete structures worldwide. During the reaction, hydroxyl and alkali (sodium and potassium ) ions react with certain siliceous compounds in the aggregate, forming a hygroscopic gel. The gel absorbs water from the cement paste and swells, possibly leading to deleterious expansion and cracking of the structure. Once ASR is detected in existing structures, there are no treatments to stop it and prolong their service life. Lithium is known to alter the reaction, as it binds to the alkali-silica gel and the latter is no longer expansive. Indeed, the use of lithium-based admixtures has been acknowledged as a preventive measure for over 50 years. In existing structures, nevertheless, the use of admixtures is no longer possible and lithium ions need to be transported into the cementitious matrix. Amongst other transport mechanisms, such as capillary absorption and diffusion, ionic migration is the most effective. In order for ionic migration to occur, power should be supplied between two electrodes, immersed in electrolytes. The reinforcement bar is often used as cathode and, therefore, attracts cations, such as lithium ions. Pore solution works as catholyte. The anolyte, on the other hand, should be a lithium compound solution. Although several studies have been conducted on the use of electric field to drive lithium ions into concrete, so far, there is no agreement on the conclusions. It is necessary to fully understand lithium migration into concrete before developing a possible treatment against ASR. This paper presents preliminary results on the investigation of the influence of different lithium compounds used as anolyte during migration through experimental testing.

The electrical resistivity of concrete can provide information about its transport properties, which is relevant for durability performance. For example, resistivity is inversely proportional to chloride diffusion, at least within similar concrete compositions. A methodology is proposed for on-site assessment of concrete cover resistance against chloride penetration, based on on-site resistivity testing. As such, resistivity testing can extend existing service life approaches to assessing on site performance. For example, the Dutch Guideline for Service life design of structural concrete (in chloride contaminated environment) is based on chloride transport testing in the prequalification stage and production control by resistivity testing of wet-cured control cubes. Adding on-site resistivity testing would extend this approach with testing for as-built quality of the concrete cover. Applying this method requires that corrections are made for the effects of reinforcing bars, inhomogeneities due to drying out and resistivity increase due to cement hydration. A correction for the presence of reinforcement can be obtained by numerical modelling based on combined (simultaneous) cover depth and resistivity measurements. Effects of hydration and drying out can be accounted for using long-term resistivity data for concrete with different cement types and water/cement ratios in different moisture conditions.

Blast furnace slag cement (BFSC) has been used to build reinforced concrete structures in marine and road environment in The Netherlands for nearly a century. The experience is good and structures with long service lives can be obtained, as has been shown by several field studies. This is caused by a high resistance against chloride penetration and a high electrical resistivity, demonstrated both in the field and in the laboratory. Due to the high slag content, related CO2 emission and embedded energy are lower than for Portland cement. In many countries including Norway, BFSC is a novelty and long term experience is lacking. In order to study the potential for use of BFSC in Norway, a desk study was carried out, reporting on many aspects. The resistance against chloride induced corrosion stands out positively, whereas neither carbonation nor frost are problems in practice. However, the Dutch experience is mainly based on CEM III/B with 65-75% of slag by mass of binder. Such a cement is not available on the Norwegian market. The introduction of CEM III/A with c. 48% slag in Norway is anticipated. Consequently, an experimental program was drawn up to study the properties of concrete made with CEM III/B and CEM III/A (with 48% slag), with and without addition of silica fume. The ultimate goal is to provide a basis for evaluation of use of slag cement in Norway for durable coastal and marine structures. This paper describes the history and performance of slag in concrete in The Netherlands, the outline of the experimental program and expected results from the study.

Betonconstructies worden niet alleen ouder; het aantal dat een respectabele leeftijd bereikt, neemt de komende decennia zelfs drastisch toe. Er is dus veel kennis nodig ten behoeve van onderhoud, reparatie en eventuele vervanging van grote aantallen betonconstructies, mede onder invloed van sterk veranderende gebruikseisen. De huidige praktijk laat echter zien dat het bepalen van de restlevensduur van die constructies niet goed mogelijk is. Een SBRCURnet-commissie heeft in juli 2014 preadvies opgesteld voor onderzoek naar de restlevensduur van bestaande betonconstructies.