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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., Materials and Environment

The elastic modulus of corrosion product (Ecp) has been reported with significant variations in the literature. This study aims to investigate the Ecp of naturally-generated chloride-induced corrosion products formed in different concrete mixes. Microstructural characterization was conducted through nano-indentation, electron microscopy and Raman spectroscopy. The corrosion products were mainly composed of a goethite matrix with portions of maghemite, independently of the concrete composition. Microscopic analysis suggest that layers of corrosion products grow at different times and under different physico-chemical conditions. Our measurements showed that Ecp varied between 80−100 GPa, which can be suggested for numerical models of corrosion induced cracking., Materials and Environment, Novel Aerospace Materials

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., Materials and Environment

The elastic modulus of corrosion product (Ecp) has been reported with significant variations in the literature. This study aims to investigate the Ecp of naturally-generated chloride-induced corrosion products formed in different concrete mixes. Microstructural characterization was conducted through nano-indentation, electron microscopy and Raman spectroscopy. The corrosion products were mainly composed of a goethite matrix with portions of maghemite, independently of the concrete composition. Microscopic analysis suggest that layers of corrosion products grow at different times and under different physico-chemical conditions. Our measurements showed that Ecp varied between 80−100 GPa, which can be suggested for numerical models of corrosion induced cracking., Materials and Environment, Novel Aerospace Materials

Although reinforcement corrosion is a well-known issue, which are the locations of the steel/concrete interface most sensitive to pitting corrosion is still an unclear issue. In this study, X-ray computed tomography is used to characterize eight 20-years-old reinforced concrete cores naturally deteriorated due to chloride-induced corrosion. The deepest and most frequent corrosion pits were observed at the portion of the reinforcement oriented to the outdoor environment and in proximity to interfacial air voids. Therefore, the presence of interfacial air voids should be considered as a relevant factor when assessing the risk of corrosion of reinforced concrete structures., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Materials and Environment

Although reinforcement corrosion is a well-known issue, which are the locations of the steel/concrete interface most sensitive to pitting corrosion is still an unclear issue. In this study, X-ray computed tomography is used to characterize eight 20-years-old reinforced concrete cores naturally deteriorated due to chloride-induced corrosion. The deepest and most frequent corrosion pits were observed at the portion of the reinforcement oriented to the outdoor environment and in proximity to interfacial air voids. Therefore, the presence of interfacial air voids should be considered as a relevant factor when assessing the risk of corrosion of reinforced concrete structures., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Materials and Environment

Although corrosion of reinforcement is a well-known issue for the construction industry, there are still open questions about some fundamentals of corrosion in reinforced concrete. These points include, among others, which are the most sensitive locations of the steel/concrete interface for pitting corrosion to initiate and to propagate. In this study, X-ray computed tomography (CT-scan) is used to characterize eight 20-years-old reinforced concrete cores naturally deteriorated due to chloride-induced corrosion. The volume loss due to corrosion of the reinforcement was quantified through image analysis of CT-scans. The volume loss of the steel was found to be higher for steel rebars embedded in Portland cement specimens rather than in blended cement specimens. Furthermore, CT-scans revealed that the deepest and most frequent corrosion pits, as well as the consequent highest volume loss of steel, were present at the portion of the reinforcement closer to the outdoor environment and in proximity to air voids at the steel/concrete interface. As a consequence, the highest decrease of structural performance of the rebars would be likely localized at those locations. Therefore, the presence of interfacial air voids should be considered as relevant factor when assessing the risk of corrosion of reinforced concrete structures., Materials and Environment

This paper presents developments over 30 years in the field of cathodic protection of steel reinforcement in concrete in The Netherlands and elsewhere. From the late 1980s major developments have been: application to large numbers of precast elements corroding due to mixed-in chloride with drilled in titanium anodes and conductive coatings; analysis of working life of systems and components and end-of-life considerations; application to prestressed structures; new anode types including galvanic systems with associated life and design considerations; numerical modelling and preventative applications. Presently, CP has become a fully accepted method of securing safety and serviceability of buildings and infrastructure. Major successes and lessons learned will be presented. Technical and non-technical developments are highlighted and some recent innovative CP systems are discussed., Materials and Environment

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., Accepted Author Manuscript, Materials and Environment

Although corrosion of reinforcement is a well-known issue for the construction industry, there are still open questions about some fundamentals of corrosion in reinforced concrete. These points include, among others, which are the most sensitive locations of the steel/concrete interface for pitting corrosion to initiate and to propagate. In this study, X-ray computed tomography (CT-scan) is used to characterize eight 20-years-old reinforced concrete cores naturally deteriorated due to chloride-induced corrosion. The volume loss due to corrosion of the reinforcement was quantified through image analysis of CT-scans. The volume loss of the steel was found to be higher for steel rebars embedded in Portland cement specimens rather than in blended cement specimens. Furthermore, CT-scans revealed that the deepest and most frequent corrosion pits, as well as the consequent highest volume loss of steel, were present at the portion of the reinforcement closer to the outdoor environment and in proximity to air voids at the steel/concrete interface. As a consequence, the highest decrease of structural performance of the rebars would be likely localized at those locations. Therefore, the presence of interfacial air voids should be considered as relevant factor when assessing the risk of corrosion of reinforced concrete structures., Materials and Environment

This paper presents developments over 30 years in the field of cathodic protection of steel reinforcement in concrete in The Netherlands and elsewhere. From the late 1980s major developments have been: application to large numbers of precast elements corroding due to mixed-in chloride with drilled in titanium anodes and conductive coatings; analysis of working life of systems and components and end-of-life considerations; application to prestressed structures; new anode types including galvanic systems with associated life and design considerations; numerical modelling and preventative applications. Presently, CP has become a fully accepted method of securing safety and serviceability of buildings and infrastructure. Major successes and lessons learned will be presented. Technical and non-technical developments are highlighted and some recent innovative CP systems are discussed., Materials and Environment

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., Accepted Author Manuscript, Materials and Environment

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 fo, Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Materials and Environment

Electrochemical lithium migration has been suggested as repair technique for alkali-silica reaction affected concrete structure. In this method, an electric field is used to transport lithium into the material. Current studies have used anolyte solutions with various lithium salts at different concentrations. However, little has been said on the effect of the anolyte on lithium migration. In this paper, an experimental study on the influence of the type of lithium compound and its concentration in the anolyte is presented. Results point out that the concentration of the solution, rather than the type of lithium salt, affected migration. The anolytes with the highest concentrations provided the highest final levels of lithium in the specimens., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Materials and Environment

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., Materials and Environment

This paper presents an overview of 30 years' experience with cathodic protection of steel in concrete in The Netherlands. Principles and practical aspects of CP and its design and installation are presented. 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 mixedin chlorides. The parties involved worked together to draw up a Technical Guideline. In the second period, application to bridges came up, 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 durability and safety. Renewed collaboration led to a database that allowed analysis of various aspects of CP system working life, including shortcomings in early systems. Major successes and lessons learned will be presented. Technical and non-technical developments are highlighted and some recent innovative CP components and systems are discussed., Materials and Environment

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 fo, Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Materials and Environment

Electrochemical lithium migration has been suggested as repair technique for alkali-silica reaction affected concrete structure. In this method, an electric field is used to transport lithium into the material. Current studies have used anolyte solutions with various lithium salts at different concentrations. However, little has been said on the effect of the anolyte on lithium migration. In this paper, an experimental study on the influence of the type of lithium compound and its concentration in the anolyte is presented. Results point out that the concentration of the solution, rather than the type of lithium salt, affected migration. The anolytes with the highest concentrations provided the highest final levels of lithium in the specimens., Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public., Materials and Environment

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., Materials and Environment

This paper presents an overview of 30 years' experience with cathodic protection of steel in concrete in The Netherlands. Principles and practical aspects of CP and its design and installation are presented. 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 mixedin chlorides. The parties involved worked together to draw up a Technical Guideline. In the second period, application to bridges came up, 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 durability and safety. Renewed collaboration led to a database that allowed analysis of various aspects of CP system working life, including shortcomings in early systems. Major successes and lessons learned will be presented. Technical and non-technical developments are highlighted and some recent innovative CP components and systems are discussed., Materials and Environment

The currently available treatment techniques for concrete structures affected by alkali-silica reaction (ASR) are limited and electrochemical lithium migration has been proposed as an alternative. Lithium compounds have shown to have beneficial effects on ASR expansion when used as admixtures to fresh concrete. During the electrochemical treatment, lithium ions area transported into concrete (or mortar) by the action of an electrical field. The same principle is behind well-established techniques such as electrochemical chloride extraction (ECE). Like during ECE treatments, the reinforcement may be used as cathode during electrochemical lithium migration. In this paper, an investigation of the use of an embedded cathode during electrochemical lithium migration is presented. Mortar specimens were cast with embedded titanium meshes, which worked as cathodes. Results showed that potassium and sodium ions accumulated in the region around the embedded mesh and, under the tested conditions, few lithium ions reached that area. The accumulation of sodium and potassium is an undesirable side effect that increases the pH, which may possibly induce further ASR development, if not enough lithium ions reach the area., Materials and Environment

Owing to the unique molecular structure and high ion exchange capacity, hydrotalcites are believed to have a potential to be modified and tailor-made as an active corrosion protective component of reinforced concrete. In this paper, two types of modified hydrotalcites (MHT-pAB and MHT-NO2) were tested both in alkaline solution and mortar for their possibilities as chloride scavengers and inhibitor release agents for application in concrete. The test in alkaline solution showed that ion exchange occurred between free chloride ions in solution and the intercalated inhibitive anions in the MHTs. The results in mortar validated that MHTs could be promising alternatives for preventing chloride-induced corrosion when an appropriate dosage is adopted and applied in a proper way, in particular, either incorporation of a certain amount (MHT-pAB to replace 5% weight of cement) in the bulk mortar or as a coating of the reinforcing steel (MHT-pAB or MHT-NO2 at 20% weight of cement)., Materials and Environment, (OLD) MSE-6

Although the steel–concrete interface (SCI) is widely recognized to influence the durability of reinforced concrete, a systematic overview and detailed documentation of the various aspects of the SCI are lacking. In this paper, we compiled a comprehensive list of possible local characteristics at the SCI and reviewed available information regarding their properties as well as their occurrence in engineering structures and in the laboratory. Given the complexity of the SCI, we suggested a systematic approach to describe it in terms of local characteristics and their physical and chemical properties. It was found that the SCI exhibits significant spatial inhomogeneity along and around as well as perpendicular to the reinforcing steel. The SCI can differ strongly between different engineering structures and also between different members within a structure; particular differences are expected between structures built before and after the 1970/1980s. A single SCI representing all on-site conditions does not exist. Additionally, SCIs in common laboratory-made specimens exhibit significant differences compared to engineering structures. Thus, results from laboratory studies and from practical experience should be applied to engineering structures with caution. Finally, recommendations for further research are made., Materials and Environment

Owing to the unique molecular structure and high ion exchange capacity, hydrotalcites are believed to have a potential to be modified and tailor-made as an active corrosion protective component of reinforced concrete. In this paper, two types of modified hydrotalcites (MHT-pAB and MHT-NO2) were tested both in alkaline solution and mortar for their possibilities as chloride scavengers and inhibitor release agents for application in concrete. The test in alkaline solution showed that ion exchange occurred between free chloride ions in solution and the intercalated inhibitive anions in the MHTs. The results in mortar validated that MHTs could be promising alternatives for preventing chloride-induced corrosion when an appropriate dosage is adopted and applied in a proper way, in particular, either incorporation of a certain amount (MHT-pAB to replace 5% weight of cement) in the bulk mortar or as a coating of the reinforcing steel (MHT-pAB or MHT-NO2 at 20% weight of cement)., Materials and Environment, (OLD) MSE-6

The currently available treatment techniques for concrete structures affected by alkali-silica reaction (ASR) are limited and electrochemical lithium migration has been proposed as an alternative. Lithium compounds have shown to have beneficial effects on ASR expansion when used as admixtures to fresh concrete. During the electrochemical treatment, lithium ions area transported into concrete (or mortar) by the action of an electrical field. The same principle is behind well-established techniques such as electrochemical chloride extraction (ECE). Like during ECE treatments, the reinforcement may be used as cathode during electrochemical lithium migration. In this paper, an investigation of the use of an embedded cathode during electrochemical lithium migration is presented. Mortar specimens were cast with embedded titanium meshes, which worked as cathodes. Results showed that potassium and sodium ions accumulated in the region around the embedded mesh and, under the tested conditions, few lithium ions reached that area. The accumulation of sodium and potassium is an undesirable side effect that increases the pH, which may possibly induce further ASR development, if not enough lithium ions reach the area., Materials and Environment

Although the steel–concrete interface (SCI) is widely recognized to influence the durability of reinforced concrete, a systematic overview and detailed documentation of the various aspects of the SCI are lacking. In this paper, we compiled a comprehensive list of possible local characteristics at the SCI and reviewed available information regarding their properties as well as their occurrence in engineering structures and in the laboratory. Given the complexity of the SCI, we suggested a systematic approach to describe it in terms of local characteristics and their physical and chemical properties. It was found that the SCI exhibits significant spatial inhomogeneity along and around as well as perpendicular to the reinforcing steel. The SCI can differ strongly between different engineering structures and also between different members within a structure; particular differences are expected between structures built before and after the 1970/1980s. A single SCI representing all on-site conditions does not exist. Additionally, SCIs in common laboratory-made specimens exhibit significant differences compared to engineering structures. Thus, results from laboratory studies and from practical experience should be applied to engineering structures with caution. Finally, recommendations for further research are made., Materials and Environment

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., Materials and Environment

For many concrete infrastructural works a service life of 80, 100 or 200 years is required. To convince owners and authorities that these requirements can be met probability-based models for service life predictions have been developed. These models are based on theoretical and experimental laboratory studies. Many of these models focus on the probability of chloride-induced rebar corrosion. For a check of the reliability of one of these models, i.e. the DURACRETE model, predicted chloride profiles have been compared with chloride profiles measured in five marine concrete structures. Lessons learned from these existing structures in view of the reliability of numerical service life predictions are presented in this paper., Materials and Environment, Cursussen

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., Materials and Environment

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, Materials and Environment

Chloride induced reinforcement corrosion is the predominant degradation mechanism affecting reinforced concrete structures. Chlorides (Cl-) contained in sea water or de-icing salts penetrate through concrete pores by diffusion and/or convection. Reinforcement corrosion initiates when the Cl concentration at the reinforcing steel surface equals or exceeds a specific concentration. This concentration is known as the critical chloride content (Ccrit). This study presents an experimental method proposed by the RILEM Committee 235-CTC "corrosion initiating chloride threshold concentrations". Two series of reinforced concrete specimens were fabricated: one with ordinary Portland cement (CEM I) and another with ground granulated blast furnace slag-GGBS- (CEM III/B) cement, both commercially available in The Netherlands. Subsequently, the specimens were partially submerged in a chloride-rich solution (3.3 wt. % NaCl) for 6 months. During this period, continuous monitoring of the open-circuit potential (OCP) of the steel reinforcement was used to determine the initiation of reinforcement corrosion. The concentration of Cl could be determined by acid digestion and subsequent titration of powder samples collected from individual layers in the concrete cover. Results show that after the exposure period, the Ccrit could be determined in PC specimens whereas in GGBS concrete specimens the higher resistance to chloride ingress prevented from obtaining corrosion initiation., Materials and Environment

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., Materials and Environment

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., Materials and Environment

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, Materials and Environment

Chloride induced reinforcement corrosion is the predominant degradation mechanism affecting reinforced concrete structures. Chlorides (Cl-) contained in sea water or de-icing salts penetrate through concrete pores by diffusion and/or convection. Reinforcement corrosion initiates when the Cl concentration at the reinforcing steel surface equals or exceeds a specific concentration. This concentration is known as the critical chloride content (Ccrit). This study presents an experimental method proposed by the RILEM Committee 235-CTC "corrosion initiating chloride threshold concentrations". Two series of reinforced concrete specimens were fabricated: one with ordinary Portland cement (CEM I) and another with ground granulated blast furnace slag-GGBS- (CEM III/B) cement, both commercially available in The Netherlands. Subsequently, the specimens were partially submerged in a chloride-rich solution (3.3 wt. % NaCl) for 6 months. During this period, continuous monitoring of the open-circuit potential (OCP) of the steel reinforcement was used to determine the initiation of reinforcement corrosion. The concentration of Cl could be determined by acid digestion and subsequent titration of powder samples collected from individual layers in the concrete cover. Results show that after the exposure period, the Ccrit could be determined in PC specimens whereas in GGBS concrete specimens the higher resistance to chloride ingress prevented from obtaining corrosion initiation., Materials and Environment

For many concrete infrastructural works a service life of 80, 100 or 200 years is required. To convince owners and authorities that these requirements can be met probability-based models for service life predictions have been developed. These models are based on theoretical and experimental laboratory studies. Many of these models focus on the probability of chloride-induced rebar corrosion. For a check of the reliability of one of these models, i.e. the DURACRETE model, predicted chloride profiles have been compared with chloride profiles measured in five marine concrete structures. Lessons learned from these existing structures in view of the reliability of numerical service life predictions are presented in this paper., Materials and Environment, Cursussen

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., Structural Engineering, Civil Engineering and Geosciences

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., Structural Engineering, Civil Engineering and Geosciences

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., Structural Engineering, Civil Engineering and Geosciences

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., Structural Engineering, Civil Engineering and Geosciences

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., Structural Engineering, Civil Engineering and Geosciences

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., Structural Engineering, Civil Engineering and Geosciences

A carbonate form of MgAl hydrotalcite, Mg(2)Al-CO3 and its p-aminobenzoate (pAB) modified derivative, Mg(2)Al-pAB, were synthesized and characterized by means of XRD, FT-IR and TG/DSC. The anticorrosion behavior of Mg(2)Al-pAB was evaluated based on open circuit potential (OCP) of carbon steel in simulated concrete pore solution and on chloride-exchange experiments. The results reported in this paper demonstrate that ion-exchange indeed occurred between chlorides and intercalated pAB anions, thereby reducing the free chloride concentration in simulated concrete pore solution. The simultaneously released pAB anions were found to exhibit the envisioned inhibiting effect and caused corrosion initiation of the steel to shift to higher chloride concentrations than without the modified hydrotalcites. © 2013 Elsevier Ltd. All rights reserved.

A carbonate form of Mg-Al-hydrotalcite with Mg/Al =2 and its p-aminobenzoate (pAB) modified derivative were synthesized and characterized by means of XRD, IR and TG/DSC. Mg(2)Al-CO3 was prepared by a coprecipitation method and was subsequently modified by pAB through the calcination-rehydration technique. The results from the relevant characterizations combined with total organic carbon (TOC) analysis further confirmed that pAB anions were successfully intercalated into the interlayer space of the hydrotalcite. The anticorrosion behavior of Mg(2)Al-pAB was evaluated on the basis of open circuit potential (OCP) monitoring of carbon steel in simulated concrete pore solution at pH 13 contaminated with chloride. The preliminary results from this study demonstrated that ion-exchange indeed occurred between free chloride ions in simulated concrete pore solution and the intercalated pAB anions in Mg(2)Al-pAB structure. The simultaneously released pAB anions were found to exhibit the envisaged inhibiting effect and cause a shift of corrosion initiation of the steel to higher chloride concentrations than without the modified hydrotalcite., Structural Engineering, Civil Engineering and Geosciences

Structural Engineering, Civil Engineering and Geosciences

This paper addresses experience from The Netherlands with blast furnace slag and fly ash in concrete in chloride contaminated environments, both from the field and the laboratory. Use of slag produced in The Netherlands started in the 1930s and CEM III/B LH HS, with typically 70% slag, became the dominant cement type in the 1970s. Approximately 10 million cubic metres of slag cement concrete are produced annually, in particular for concrete cast in situ. The low heat of hydration is seen as a big advantage. Fly ash has been used since the 1980s at typically 27% replacement level. Traditionally slag and fly ash were intermixed with clinker in the cement plant and sold as “cements”. The manufacturer would carefully compose these products to have similar 28 day strength as Portland cement, typically 32.5 or 42.5 MPa. In the 1990s CEM III/A 52.5R was introduced, with 52-57% slag, aimed at the precast industry. Recently, separate slag for addition to Portland cement in the concrete mixing plant has become available. Traditional concrete technology for aggressive environments involves about 340 kg cement per cubic meter, a w/c of 0.43 and rounded siliceous aggregate of 32 mm maximum size., Structural Engineering, Civil Engineering and Geosciences

Against the background of immense costs of repair or replacement of concrete structures degraded by reinforcement corrosion, a strong interest in industry and research can nowadays be found in the underlying processes and in possibilities to influence them. As a part of the reinforcement corrosion circuit, the resistivity of concrete is a decisive material parameter with regard to corrosion propagation, which itself is a time-dependent process of many years of length. For this reason, a picture of the long term behaviour of the resistivity of concrete could be of great value. This paper presents resistivity data of concrete specimens up to an age of 17 year. An investigation was carried out of their development throughout the years in dependence of all main aspects influencing the magnitude and the development of the resistivity (climate, cement type, water/cement-ratio)., Structural Engineering, Civil Engineering and Geosciences

Most high filler concrete studies are based on relatively high contents of powder (cement + filler) (>400 kg m-3). This paper aims to increase the total fly ash content relative to the clinker content, while simultaneously minimizing the total powder content in the concrete to values lower than 300 kg m-3. The motivation for decreasing the total powder content using fly ash as a cement replacement is based on the fact that concrete structures often have an ‘overstrength’ related to excess cement. Consequently, there is potential for using lower amounts of clinker and replacing it by filler, which can reduce the amount of primary raw materials used and CO2 related to clinker production. However, the question arises if sufficient durability of this ‘high filler’ concrete is achieved. In this paper chloride penetration resistance is measured by rapid chloride migration and diffusion tests on both laboratory mixes and samples from pilot projects. Also, electrical resistivity and polarization-and-fluorescence microscopy (PFM) are used to evaluate the development of the microstructure in time. The results show possibilities and limitations of high filler concrete in achieving long service life., Structural Engineering, Civil Engineering and Geosciences

Structural Engineering, Civil Engineering and Geosciences

Modern service life design methods for concrete structures use chloride diffusion data as an input parameter. Abundant data exist for concrete at 28 days and, to a lesser extent, at later ages. This paper presents chloride diffusion data for mortar at ages between 1 day and 28 days age. Rapid Chloride Migration (RCM) and natural diffusion tests are performed on mortar specimens made with Portland (CEM I) and Blast Furnace Slag (CEM III/B) cement with w/c 0.50. The results show that mortar at a young age has a relatively high chloride migration coefficient. The value for CEM I at day 1 is one order of magnitude larger than at 28 days age, for CEM III/B this value is even two orders of magnitude larger. In the first two weeks, the value drops rapidly and more strongly for Blast Furnace Slag cement. The experimental data was used to model the chloride ingress up to 50 years with and without exposure to chloride at young ages. Modelling shows that the effect of exposure at young age is significant but relatively small when compared to the chloride ingress during the whole service life of concrete., Structural Engineering, Civil Engineering and Geosciences