The content of chlorides in concrete designs: a probabilistic approach to compliance assessment with due regard to the measurement uncertainty

摘要

A major factor for the durability of concrete is the protection against corrosion of reinforcing steel. One out of some corrosion agents are dissolved chlorides. Therefore, their contents are limited in the raw materials and subject to a compliance assessment. The concrete standard EN 206-1 provides both a semi-probabilistic calculation method for the design of concrete as regards the input of chlorides through the components and a decision rule for compliance assessment. This paper describes a full probabilistic approach to the compliance assessment taking into account the heterogeneity of the components and the uncertainty of testing. The content of Cl− is defined as the sum of gamma-distributed parameters. The uncertainty data are taken from the test procedures and from effects due to sampling procedures. The proposed approach is quantified for a high-performance and for a simple concrete. It allows calculating upper limits of chloride contents according to the client’s requirements for conformity and/or for producer’s/consumer’s risks. Additionally discussed are the particular financial consequences of incorrect decisions. Major results of the application of the probabilistic approach are that the upper limits of the chloride contents are comparable to those of the semi-probabilistic one and that the risks for high-performance concretes are not negligible. The decision rule given in EN 206-1 is easy to apply but not unambiguous. The probabilistic approach permits to define concepts for decision rules based on the probability of conformity or on the appropriate risks. For risk-based concepts, the individual performance of the testing laboratory can be taken into account.