## 2 Materials and Methods
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Mortar**} & \multirow{2}{*}{**Aggregate**} & \multirow{2}{*}{**Cement**} & \multirow{2}{*}{**Water/Cement**} & \multirow{2}{*}{**Aggregate**} & \multicolumn{2}{c}{**Admixtures [\%]**} \\ \cline{6-8}  & & & & & **Size [mm]** & **Air Entrainer** & **Rheological** \\  & & & & & **Agent** & **Agent** \\ \hline A\({}^{\text{EC}}\) & Expanded clay & & 0.90 & & - & - \\ \hline B\({}^{\text{GEC}}\) & \
\begin{tabular}{c} Granular \\ expanded cork \\ \end{tabular} &
\begin{tabular}{c} CEM II \\ 32.5N \\ \end{tabular} & 1.00 & & & - & - \\ \hline C\({}^{\text{AERO}}\) & Silica aerogel & 32.5N & 0.90 & & 0.5 & 0.075 \\ \hline D\({}^{\text{REF}}\) & \multirow{2}{*}{Sand} & \multirow{2}{*}{0.65} & \multirow{2}{*}{} & - & - \\ \cline{6-8} E\({}^{\text{AD}}\) & & & 0.55 & & 0.5 & 0.075 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Composition of the mortars produced. The following physical and mechanical properties of the mortars at room temperature (reference condition) and after exposure to elevated temperatures were assessed: bulk density, ultrasonic pulse velocity, Young's modulus, dynamic shear modulus, Poisson ratio, compressive strength, and thermal conductivity. The compressive strength was indirectly estimated based on the values of the Young's modulus [40]. In particular, the relationship between those two properties obtained by [PERSON] et al. [41, 42] was considered. The main procedures of these tests, performed according to European and American standards [43, 44, 40, 45], are described next. The bulk density of the mortars in the hardened state was determined by the geometrical principle established in EN 1015-10 [43], based on the measurement of the actual dimensions of each specimen (considering the average of three measurements) and of its weight using a scale with an accuracy of \(\pm\) 0.1 g. The bulk density can be readily calculated based on the volume and mass values of the test specimens. The ultrasonic pulse velocity test was performed on prismatic specimens according to EN 12504-4 [44]. Although this standard was developed for concrete, it is also applicable to mortars. A Proceq Pundit Lab + equipment was used, connected to two 54 kHz frequency transducers; vaseline (a blend of mineral oils and waxes) was applied as contact material at the interfaces between the test specimens and the two transducers. The Young's modulus was determined in prismatic specimens as specified in American Society for Testing and Materials (ASTM) standard E1876-01 [40] (non-destructive test), using a GrindoSonic MK5 \"Industrial\" equipment. This equipment consists of a sensor and an electronic system that captures the resonant frequency of the test specimen, placed on supports located at the fundamental nodal points, that vibrates due to the strike of a drumstick (Figure 2). An Isomet 2114 equipment [45, 46] was used to determine the thermal conductivity of the specimens, following the ASTM standard D5930-09 standard. The test was performed using a surface probe placed on the surface of the specimen, which analyses the thermal response to thermal impulses transmitted by the probe. The tests were performed on the cylindrical specimens (diameter of 60 mm and thickness of 20 mm). In these tests, the surface of the test specimens should be as flat as possible  
Figure 1: Thermal chamber before the tests. Figure 2: GrindoSonic MK5 equipment (left); test to obtain flexural vibration frequency (center); test to obtain torsional vibration frequency (right). in order to maximize the contact surface with the probe. In order to minimize the effect of abrupt temperature and ambient humidity variation, the test specimens were wrapped in adherent film and placed on an EPS plate 12 h prior to the test, for a dry state test at \(\approx\) 20 \({}^{\circ}\)C. Due to limitations of the available materials, this test was only performed for the control temperature, 150 \({}^{\circ}\)C and 250 \({}^{\circ}\)C.