## 4 Measuring Techniques  
When considering the nature of measurement, [PERSON] et al. [4] divided common techniques for measuring the chloride content and estimating the diffusion coefficient in concrete structures in laboratory and field techniques. Laboratory techniques are performed on specimens, and the most common of these techniques are the rapid chloride permeability test (RCPT), non-steady state diffusion test, ponding test, electrical migration test, etc. Laboratory tests are mostly used to determine concrete properties regarding the chloride ingress. Using laboratory tests, certain properties, such as the diffusion coefficient, ageing coefficient, temperature dependence, etc., can be assigned to a specific concrete mixture. The non-steady state diffusion tests are deemed as the most covered laboratory tests when considering the extent and attention given in the literature. These tests are described in [44; 45; 46; 47]. On the other side, field techniques can be further divided into destructive (performed on extracted cores) and non-destructive techniques. When performing field destructive techniques, samples are taken from in-service structures, and chloride profiles are determined by using physical or chemical lab techniques. Quantitative X-ray diffraction analysis is deemed as being representative of physical destructive techniques while the most common chemical techniques are the Volhard method and potentiometric evaluation. Non-destructive techniques (NDTs) comprise methods that do not alter the future usefulness of the material where the measurement is taken. According to [4], the most developed and studied NDT methods could be categorized as ion selective electrodes (ISEs) [48; 49], electrical resistivity (ER) [50; 51], and the optical fiber sensor (OFS) [52; 53]. When observing all the presented techniques, the most common are field destructive tests, from which the most popular are the potentiometric and Volhard method. For the needs of short-term decision-making, e.g., repair or maintenance, these techniques are of essential value. However, they can also be used for model updating [54; 55]. A round-robin test with 30 laboratories on chloride analysis in concrete was carried out by the Technical Committee TC 178-TMC of the International Union of Laboratories and Experts in Construction Materials, Systems, and Structures (RILEM), in which it was found that the most suitable method for total chlorides (extraction and quantification) is the Volhard method [56]. Furthermore, in [56], the repeatability and reproducibility of the Volhard method were elaborated. The repeatability was shown to be independent of the actual value, with an average of 0.0135. The reproducibility showed a linear dependency on the actual value, according to the equation, \(R=0.1312\,(\%\text{CI})+0.0152\), with a correlation coefficient, \(r\), of 0.994. When considering destructive methods, such as the Volhard method, errors in measurement depend mainly on different steps of the protocol, such as grinding, preparation of powder, acid attack, dilution, and concentration measurements. [PERSON] et al. [57] analyzed 42 chloride content measurements in order to assess the total measurement error by considering three main errors (protocolerror, sample error, and human error). The probability of the detection of corrosion initiation was expressed as a function of the margin between the critical concentration and the real concentration, i.e., \(C(t)-C_{crit}\). For a margin of 0.0001 (by weight of concrete), the probability of detection was found to be around 87%. This margin corresponds to approximately 0.1 wt.-%/c (by weight of cement). However, besides the accuracy of the testing method, the uncertainties in measurement consist of spatial variability, the number of measurements taken, etc. Thus, when performing an analysis of the VoI, it is not possible to assign an exact cost or accuracy to a measurement event, in such a way that it covers all stated methods of measurement.