## 5 Finite Element Code
### Basic Characteristics of Finite Element Code
This is an excellent example of the care that must be taken when adding additives, as one property may be enhanced, however other properties could be detrimentally altered. ### Restoration Mortars

Reverse engineering emerges as the ideal methodological approach for the design and production of compatible and performing restoration materials [66]. The main steps (Figure 35) of this methodological approach are: (i) characterization of historical materials in order to select similar raw materials for the production of the restoration mortars and design the mortar mixture directives, always taking into account that the historical mortar is a disturbed system and is not the system that was initially produced and applied; (ii) preparation of restoration mortars, i.e., the production of designed mortar mixes; (iii) evaluation of the restoration mortar properties, in terms of fresh mortar characteristics, such as workability, bulk density, retained water, air content, etc., as well as in terms of the mortar characteristics during setting and hardening, i.e., the evolution and final state of chemical phases, microstructural characteristics and acquired mechanical strengths; (iv) optimization of the mortar mixes, which allows for modifications of the mortar mix in order to obtain the best possible characteristics; and (v) pilot application on the cultural heritage asset in order to assess the restoration mortar on masonry scale [231]. This methodology has been enhanced and NDTs can assist the evaluation, especially in the final step of pilot application [70]. Restoration mortars based on traditional materials and techniques can be separated into categories [231], as shown in Table 6, while the use of cement in any quantity should be avoided [69] due to the incompatibility it presents and the subsequent deterioration of the historical materials [56]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{4}{c}{**Restoration Mortar**} & \multicolumn{2}{c}{**Historical Mortar**} \\
**Motar Type** & \multicolumn{2}{c}{**Compressive**} & \multicolumn{2}{c}{**Flexural**} & \multicolumn{2}{c}{**Tensile Strength**} \\  & **Strength (MPa)** & \multicolumn{2}{c}{**Strength (MPa)**} & \multicolumn{2}{c}{**(MPa)**} \\ \hline Typical lime mortars & 1.1–1.2 & 0.3–0.4 & 0.2–0.3 & \textless{}0.35 \\ Hydraulic lime mortars & 2.9–4.9 & 0.5–0.7 & 0.4–0.5 & 0.35–0.55 \\ Lime-pozzolan mortars & 0.9–1.6 & 0.4–0.4 & 0.3–0.3 & \textgreater{}0.60 \\ Lime-crushed brick mortars & 1.1–2.0 & 0.3–0.4 & 0.2–0.3 & \textgreater{}0.60 \\ Hydraulic lime-crushed brick mortars & 3.4–5.2 & 0.7–1.8 & 0.5–1.2 & \textgreater{}0.55 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Mechanical properties of restoration mortars after nine months of hardening according to [PERSON] et al. [231] and of historical mortars of each type [66]. Figure 35: Basic methodological framework for restoration mortar design and assessment. The analysis of many historical mortars has allowed researchers to establish requirements that the raw materials used to produce restoration mortars for historical structures must comply with [231]. An interesting example of the lessons we can learn from the craftsmen of the past is related to the firing temperature of the bricks which will be crushed and used as raw materials in lime-crushed brick mortars, where scientists have discovered that the pozzolanic reaction and the best mortar characteristics are acquired when the brick has been fired at low temperatures, lower than firing temperatures today. In recent years, researchers have studied the use of metakaolin, an extremely active artificial pozzolan, which contributes to the production of mortars with excellent characteristics [232]. Compatibility is a quite complex term, as it is assessed chemical, dimensional, hygric, aesthetical, adhesion, mechanical and bioecological terms [69]. [PERSON] et al.