## 4 Discussion  
The experimental results are presented in Table 2 in terms of: (i) the average--for each group of identical specimens--temperature recorded by the TKLE, TKFE, and TKM thermocouples at the end of 1 h exposure to the target furnace temperature, (ii) the maximum textile axial stress (\(\sigma_{max}\)) computed as the ratio of the maximum load carried by the TRM overlay to the cross sectional area of the longitudinal (load-aligned) fibers (equal to 6.545 mm\({}^{2}\) for the single-layer TRM overlay and 13.090 mm\({}^{2}\) for the double-layer one), (iii) the corresponding relative displacement of the textile with respect to the wall (\(d_{r,max}\)) being equal to the average of the readings from the DDG at the loaded end and (iv) the corresponding textile slip from within the mortar (\(s_{max}\)) being equal to the average of the readings from the DDG at the free end. As far as the thermocouples' readings are concerned, temperature values do not vary significantly in relation to the sensors' position (per specimens' group), the number of textile layers (per mortar type), and the type of mortar (for the same number of textile layers). The TRM surface temperature and the temperature of the projected textile close to the loaded and free end for all types of TRM overlays investigated are found to be equal to roughly half of the ambient air temperature (for both mortar types: 50 \({}^{\circ}\)C for single-layer TRM overlays exposed to 120 \({}^{\circ}\)C; \(\sim\)110 \({}^{\circ}\)C and \(\sim\)120 \({}^{\circ}\)C for single-layer and double-layer TRM overlays exposed to 200 \({}^{\circ}\)C, respectively). In more detail, the rate of TRM surface and textile temperatures over the nominal exposure (air) temperature increase with increasing exposure temperature. The evolution of the thermocouples' values during the hour-long exposure is depicted in Figure 6 for three representative specimens furnished with TRLM overlays (the respective temperature records concerning specimens with TRNM overlays are almost identical). Figure 5: Specim at failure. The maximum textile axial stress, \(\sigma_{max}\), (average for each specimen group) versus the target furnace temperature plot is presented in Figure 7a for each type of mortar. It is observed that, at control conditions (non-heated specimens: 20 \({}^{\circ}\)C in Table 2) and after exposure at a nominal air temperature of 120 \({}^{\circ}\)C, both single-layer TRM systems (TRNM and TRLM) exhibit similar bond capacity differences between them being unimportant considering the statistical performance of each pair of compared specimen groups. The same does not apply for the nominal exposure temperature of 200 \({}^{\circ}\)C for which single-layer and double-layer TRNM overlays outperform the respective TRLM ones in terms of residual bond capacity. Figure 6: Thermocouples’ temperature profiles for representative specimens: (**a**) T120S1L03, (**b**) T200S1L03, and (**c**) T200S2L02. Figure 7: (**a**) Maximum textile axial stress, \(\sigma_{max}\), and corresponding (**b**) relative displacement, \(d_{r,max}\), and (**c**) slip, \(s_{max}\), versus nominal exposure temperature. Per type of matrix considered, the following trends are observed. For the same thermal treatment prior to testing (none, or exposure at either 120 \({}^{\circ}\)C or 200 \({}^{\circ}\)C for 1 h), \(\sigma_{max}\) stresses corresponding to double-layer overlays are comparable to those of single-layer ones (as also noticed by [PERSON] and [PERSON] [6] for specimens tested without having been previously heated). The effect of exposure temperature increase prior to testing does not seem to substantially affect the residual bond capacity of single-layer and double-layer TRNM overlays. The maximum textile axial stress remains almost unchanged for specimens subjected to 120 \({}^{\circ}\)C and decreases by less than 10% for specimens subjected to 200 \({}^{\circ}\)C in comparison with the maximum textile axial stress of the reference specimens. The same does not apply for TRLM overlays.