## 2 Materials and Methods  
Five types of mortars were produced: three thermal mortars, containing 100% of expanded clay (A\({}^{\text{EC}}\) mortar) with bulk density of 550 kg/m\({}^{3}\) and Euroclass A1 of reaction to fire; 100% of granular expanded cork (B\({}^{\text{GEC}}\) mortar) with bulk density of 55 kg/m\({}^{3}\) and thermal conductivity of 0.039 W/(m.K); or 100% of a commercial silica aerogel (C\({}^{\text{AERO}}\) mortar) with bulk density between 80 and 100 kg/m\({}^{3}\) and thermal conductivity between 0.01 and 0.031 W/(m.K); one reference mortar (D\({}^{\text{ref}}\) mortar) based on silica sand with bulk density of 1520 kg/m\({}^{3}\); and one silica sand mortar (E\({}^{\text{AD}}\) mortar) with admixtures (anionic surfactant (Hostapur OSB) as air entrainer agent, and methyl-hydroxyethyl-cellulose as rheological agent). The aggregate properties mentioned above are the ones provided by the manufacturers datasheets (expanded clay 0-2 from Argex; expanded cork from Amorim; Lumina aerogel PS100 particles from Cabot; and APAS 60 sand from Ariepor). The composition of each mortar is shown in Table 1. The water/cement ratios were based on EN 1015-2 [36] flow value parameters for bulk density of fresh mortar on mortars without admixtures. Since the standard EN 1015-3 [37] does not include the use of admixtures in its scope of use, for mortars with admixtures the water/cement ratios were the ones that allowed a good workability for each mortar. The water/cement ratios for mortars without admixtures were defined according to flow value parameters for bulk density of fresh mortar in line with EN 1015-2 [36]. An aggregate to water volumetric ratio of 1:4 was used for the production of all mortars, a very common ratio for conventional cement-based mortars [38]. In addition, the same binder was used in all mortars--Portland cement type CEM II B/L 32.5 N.  
In total, five batches were produced for each mortar, each one for a given target exposure temperature. The particle grading sizes used for the studied mortars were selected with fraction sizes from 0.5 to 1 mm and from 1 to 2 mm, in agreement with the grain sizes of the thermal insulating aggregates. For each mortar, five prismatic samples measuring 160 \(\times\) 40 \(\times\) 40 mm\({}^{3}\) were produced for mechanical strength tests (except for mortar C\({}^{\text{AERO}}\), for which 3 prismatic samples were produced) and two cylindrical samples with 60 mm of diameter and 20 mm of thickness were produced for thermal conductivity measurements. All the samples were stored and cured according to the EN 1015-11 standard [39]: they were first cured in polyethylene bags (7 days) and then subjected to dry curing (21 days) in a climatic chamber under controlled conditions of 20 \({}^{\circ}\)C \(\pm\) 2\({}^{\circ}\)C and relative humidity of 65% \(\pm\) 5%. After removal from the molds and completion of the curing process, the samples were exposed to the following elevated temperatures inside a [PERSON] ventilated thermal chamber: 100 \({}^{\circ}\)C, 150 \({}^{\circ}\)C, 200 \({}^{\circ}\)C and 250 \({}^{\circ}\)C. Each batch of mortar specimens was heated at a rate of 2.5 \({}^{\circ}\)C/min (air temperature inside the thermal chamber) up to the target temperature, which was kept constant during a soaking period of 1 hour (to ensure thermal equilibrium in the specimens), and then cooled to ambient temperature at a rate of \(-\)1.5 \({}^{\circ}\)C/min; these relatively low heating/cooling rates aimed at minimizing the internal stresses due to temperature gradients (Figure 1). Before being subjected to the different characterization tests (described below), the specimens were placed back in the climatic chamber for 24 h.