## 1 Introduction
However, this value can be affected by the polarisation effect of the electrodes, causing a difference between the potential applied by the power source and the potential applied across the concrete specimen [25; 34]. Moreover, the test conditions, namely the electrical current and temperature, are not constant during testing [28]. In addition, the hypothesis of constant electrical field across the specimen is only approximate [22]. However, [PERSON] et al. [28] found that the \(D_{cl,RCMT}\) is not significantly affected by the applied voltage, for the usual range considered in this test. According to [PERSON] [6], the RCMT resolution increases with the penetration depth. [PERSON] et al. [26] also reported an increase of the sample mass during the RCMT related to further water uptake, which also affects the RCMT model. As underlined in NTBuild 492 [24], the \(D_{cl,RCMT}\) cannot be directly compared with the chloride diffusion coefficient obtained from diffusion tests, since it involves different mechanisms. However, to assess the validity of the RCMT, some authors have related this test with others, such as the long-term IT, which, as mentioned may be more representative of real exposure conditions [1; 8; 10; 11; 26]. A reasonable correlation has been found between the chloride diffusion from non-steady-state diffusion tests and the \(D_{cl,RCMT}\), although the later tends to be higher [1; 8; 10; 11; 26]. This is attributed to the different chloride binding capacity and ionic interaction and activity in both tests [10; 35]. According to [PERSON] et al. [36] and [PERSON] et al. [9], the RCMT may be less conservative than the IT from NT Build 443 [37], since the chloride binding capacity may be reduced. The Chlortest project [5], involving the collaboration of various European countries, found that the RCMT could be correlated with the IT from NT Build 443 [37]. The tests were carried out for different concrete compositions, with distinct water/binder ratios (w/b) (0.40, 0.45) and types of binder (ordinary Portland cement (CEM I), silica fume (SF), fly ash (FA) and blast furnace slag (BFS)). In addition, a higher repeatability and reproducibility in the RCMT than in NTBuild 443 [37] was reported [5]. [PERSON] et al. [38] reported a high correlation between the RCMT and the IT (35 days in 165 g/dm\({}^{3}\) NaCl), for 28 days-cured concrete with w/b ranging from 0.30 to 0.70. Similarly, [PERSON] et al. [35] found a high correlation between the RCMT and the IT results for concrete with 100% CEM I, with 8 weight percentage (wt%) replacement of SF, or with 70 wt% replacement of BFS. [PERSON] et al. [10] found a poor correlation between the \(D_{cl,RCMT}\) and the diffusion coefficients of concretes with FA immersed in a NaCl solution for 28 and 225 days. This was related to the early age testing of RCMT that did not allow the sufficient reaction of FA. A reasonable relationship between the RCMT and NTBuild 443 [37] was found by [PERSON] et al. [9], considering concrete with 12% and 27% FA, tested at 90 days, to allow a more efficient contribution of this addition. The influence of the type of aggregate in the relation between the RCMT and other tests has been barely studied. Noteworthy is the study of [PERSON] et al. [10], involving a narrow set of lightweight aggregate concrete (LWAC) and normal weight concrete (NWC) compositions. The authors reported the same trend for the diffusion coefficients in the RCMT and the long-term IT, up to 225 days. However, the participation of lightweight aggregates (LWA) is known to depend on the exposure conditions and concrete composition, which may affect the validity of the RCMT [10; 39; 40]. Further research is needed in this domain. Despite involving different chloride penetration mechanisms, the RCMT is also adopted for service life models involving other exposure conditions [27; 41].