often have metallic parts which can interfere with the results and the relaxation time can be affected by the temperature9. A summary of the setup of these non-intrusive techniques used to study the drying is presented in Fig. 1. It is clear from (a) that the main difference between X-ray and neutron tomography is the beam source, which is orders of magnitude more complex and more expensive for the latter as it relies on a nuclear reactor to provide the high intensity neutron beam. Also, from the setup of the NMR (b) and GPR (c), it is possible to see that the resulting data is essentially 1D. Fig. 1. Experimental layout of the imaging techniques, (a) is the setup of the X-ray or neutron tomography, (b) represents the nuclear magnetic resonance tests and (c) describes the function of the ground penetrating radar. The comparison between neutron and X-ray can be seen in (d), where the difference of interaction of each element with the different sources is also presented. Adapted from Stelzner et al.9, Felicetti et al.7 and Dauti et al.8. Finally, from Fig. 1 (d), it is evident that the higher scattering of neutrons by hydrogens results in a more pronounced contrast between the regions rich in water and dry areas, as seen from the radial slice. Thus, the neutron tomography analysis was chosen to be applied for studying refractories castables as a complement to the works performed by Barakat et al.9, which was based on using NMR. Thus, the current study aims to present the very first (to the best of the authors’ knowledge) direct observation of the drying in a refractory material using neutron tomography. This is an important advance as it can directly benefit the other two main fronts of development and studies of the drying of refractory castables: the numerical modelling and the industrial perspectives, as seen in Fig. 2. Fig. 2. The three main pillars on the study of the drying of monolithics. The current work is a fundamental advance on the experimental tests category, which can bring progress to both the numerical models and the industrial perspective.