## 3 Results  
### General Model  
#### 3.1.1 Regression Curves  
In a useful and effective mathematical model that describes the real phenomenon, it is necessary to deal with two broad types of uncertainties [28]: aleatory uncertainties (also called inherent variability or randomness) and epistemic uncertainties. The former (aleatory) uncertainties are those that are inherent in nature or processes and cannot be influenced neither by the observer nor the manner of the observation. Such kind of uncertainty is present in the input variables of the F/T phenomenon as randomness in the F/T cycles, used material, quality of production etc. In contrast, the latter (epistemic) uncertainties are those that arise from our lack of knowledge. They stem from human choice to simplify matters, from errors in measuring observations, and last, but not least, from the finite size of the observation samples. They are typically present in the model parameters (i.e., chosen descriptive functions or relations between the variables). It should be noted that, whereas aleatory uncertainties are irreducible, epistemic uncertainties are reducible, e.g., by using improved models, more accurate measurements, and the collection of additional samples. However, in reality, it is hard to distinguish between both types; therefore, some simplifications are used when dealing with both types of uncertainties. Based on the experimental data, obtained by [9] and briefly described in Section 2.1, the following input parameters (independent variables) are used in the model under consideration, proposed in Section 2.2:  
* Number of F/T cycles, described by a uniform variable;
* Type of mortar, described by a discrete variable, with 0 for lime mortar and 1 for lime mortar with blastfurnace slag additive. As output parameters (dependent variables), [PERSON]'s modulus and ductility are used. Figure 1 shows the variation of [PERSON]'s modulus, \(E_{w}\), of wallets built of mortar M1 and M3a as a function of the number of F/T cycles. \(E_{w}\) of wallets M3a is, in principle, in the initial state before F/T, which is much higher compared to wallets M1. Before F/T, the average value of [PERSON]'s modulus amounts to 3.72 MPa for wallets M3a and 1.43 MPa for wallets M1. Such results can be attributed to the stronger bond achieved between bricks and mortar in the case of mortar M3a regardless of the fact that mortar M3a was found to be weaker by the compressive and bending tests of mortar prisms. The importance and influence of the contact area between the brick and mortar on the compressive strength of the brick masonry walls has also been emphasized by other authors [29; 30]. After 50 F/T cycles, [PERSON]'s modulus for both types of wallets slightly increased, namely by 3.85 MPa for wallets M3a and 1.73 MPa for wallets M1. This is most likely due to favorable conditions for the setting in the climatic chamber. After 100 F/T cycles, the differences in terms of the trend of the change of the Young's modulus between the two types of mortar was clearly observed. For wallets M3a, the values were reduced at 3.55 MPa, while for wallets M1, there was a moderate increase at 1.79 MPa. Damage due to F/T apparently had no negative effect on wallets M1. In contrast, there was an increase in [PERSON]'s modulus. On the other hand, for wallets M3a, the effect of damage after 100 F/T cycles was reflected in a reduction of [PERSON]'s modulus. After 150 F/T cycles, there was a reduction of [PERSON]'s modulus both by wallets M1 as well as wallets M3a, namely at 1.61 MPa for wallets M1 and 2.82 MPa for wallets M3a. The reduction rates as well as the trend shown in Figure 1 are typically higher for wallets M3a than wallets M1. The projection after 200 F/T cycles, which is based on the extrapolation based on graphs from Figure 1, shows about a 17% reduction for wallets M1 and a 56% reduction for wallets M3a compared to the initial values.