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Civil Engineering and Geoscience

Effects of slag and fly ash in concrete in chloride environment

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 EngineeringCivil Engineering and Geoscience

Effects of slag and fly ash on reinforcement corrosion in concrete in chloride environment: Research from the Netherlands

A review is given of research on the durability performance of concrete made with blast furnace slag and fly ash related to chloride induced reinforcement corrosion, carried out in the Netherlands, where slag has been used in cement for almost a century. Results are presented from field studies on concrete in marine environment and laboratory studies involving chloride exposure. Chloride surface content, diffusion coefficient, electrical resistivity, critical chloride content and corrosion rate are discussed. Both slag and fly ash concrete show improved behaviour compared to ordinary Portland cement in aggressive environments, in particular where penetration of chloride presents the risk of reinforcement corrosion.Structural EngineeringCivil Engineering and Geoscience

Electrical resistivity testing for as-built concrete performance assessment of chloride penetration resistance

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 EngineeringCivil Engineering and Geoscience

Incorporating cracking of concrete on chloride ingress and service life modeling of concrete structures

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 Environmen

Cathodic protection of steel in concrete-experience and overview of 30 years application

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 Environmen

Critical chloride concentrations in reinforced concrete specimens with ordinary Portland and blast furnace slag cement

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 Environmen

Chloride Ingress of Carbonated Blast Furnace Slag Cement Mortars

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.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 Environmen

A feasibility study of anticorrosion applications of modified hydrotalcites in reinforced concrete

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 EngineeringCivil Engineering and Geoscience