The chloride content at which reinforcement corrosion initiates in concrete is usually referred to as “chloride threshold value” or “critical chloride content” (Ccrit). As has been shown in a recent review [1], many aspects of chloride induced reinforcement corrosion in concrete are still incompletely understood and huge differences from virtually 0 to more than 3% chloride by cement weight are reported for Ccrit in the literature. There are various reasons for this, such as experimental inaccuracies (limited measurement precision, sampling methods, etc.) or localized corrosion initiation being a stochastic phenomenon. Nevertheless, also the numerous types of experimental procedures and setups being used by different laboratories are considered a major factor contributing to the scatter of literature values for Ccrit. This involves parameters such as specimen geometry, specimen preparation, concrete mix design, curing, methods to accelerate chloride ingress, electrochemical methods to detect corrosion initiation, sampling procedures, etc. This situation led in 2009 to the formation of a RILEM Technical Committee (TC 235-CTC) with the aim of proposing a realistic and feasible test procedure. Preliminary results of a round-robin test carried out with a test procedure selected on the basis of a careful state of the art report revealed that a few more challenges need to be addressed. Thus an additional effort has to be made in developing a standardized test method for the determination of Ccrit. The outcome of the mentioned RILEM Technical Committee will provide a sound basis for this. It may be combined with new insights gained over the last years such as probabilistic aspects related to specimen size [2] or challenges with corrosion initiation detection with certain binders such as slag, e.g. Ref. [3]. Also the currently running research project funded by the Swiss Federal Roads Office that aims at determining Ccrit in samples taken from field structures (rather than laboratory made samples) will provide useful experience. In this paper, advantages and disadvantages of the numerous test methods for measuring Ccrit proposed in the literature are discussed e.g. with respect to practice-relationship, experimental time / acceleration of real-world processes, applicability to different cement types, and relevance of the obtained results. The discussion also relates this to the different objectives that determining Ccrit may have, viz. if input parameters for service life modeling are the desired output or if the method is applied for comparative purposes only, e.g. for ranking materials (steel types, binders, etc.).
A critical analysis of proposed test methods for measuring the chloride threshold value in reinforced concrete
ELSENER, BERNHARD
2014-01-01
Abstract
The chloride content at which reinforcement corrosion initiates in concrete is usually referred to as “chloride threshold value” or “critical chloride content” (Ccrit). As has been shown in a recent review [1], many aspects of chloride induced reinforcement corrosion in concrete are still incompletely understood and huge differences from virtually 0 to more than 3% chloride by cement weight are reported for Ccrit in the literature. There are various reasons for this, such as experimental inaccuracies (limited measurement precision, sampling methods, etc.) or localized corrosion initiation being a stochastic phenomenon. Nevertheless, also the numerous types of experimental procedures and setups being used by different laboratories are considered a major factor contributing to the scatter of literature values for Ccrit. This involves parameters such as specimen geometry, specimen preparation, concrete mix design, curing, methods to accelerate chloride ingress, electrochemical methods to detect corrosion initiation, sampling procedures, etc. This situation led in 2009 to the formation of a RILEM Technical Committee (TC 235-CTC) with the aim of proposing a realistic and feasible test procedure. Preliminary results of a round-robin test carried out with a test procedure selected on the basis of a careful state of the art report revealed that a few more challenges need to be addressed. Thus an additional effort has to be made in developing a standardized test method for the determination of Ccrit. The outcome of the mentioned RILEM Technical Committee will provide a sound basis for this. It may be combined with new insights gained over the last years such as probabilistic aspects related to specimen size [2] or challenges with corrosion initiation detection with certain binders such as slag, e.g. Ref. [3]. Also the currently running research project funded by the Swiss Federal Roads Office that aims at determining Ccrit in samples taken from field structures (rather than laboratory made samples) will provide useful experience. In this paper, advantages and disadvantages of the numerous test methods for measuring Ccrit proposed in the literature are discussed e.g. with respect to practice-relationship, experimental time / acceleration of real-world processes, applicability to different cement types, and relevance of the obtained results. The discussion also relates this to the different objectives that determining Ccrit may have, viz. if input parameters for service life modeling are the desired output or if the method is applied for comparative purposes only, e.g. for ranking materials (steel types, binders, etc.).
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