*2.2. Methods*

All tests carried out in the experimental program are described in Table 3.

**Figure 1.** Sheep wool fiber used: (**a**) 1.5 cm long (**b**) 3.0 cm long.


**Table 1.** Apparent bulk density of the constituents.

Table 2 presents the composition of the mortars produced in this work.


**Table 2.** Composition of the mortar mixes by mass.

**Table 3.** Experimental campaign tests.


For the hardened mortar tests, prismatic samples (40 mm × 40 mm × 160 mm) were used, in accordance with European Standards.

For ultra-sound pulse velocity, the direct and indirect methods were used for the measurements. In the direct transmission method, the electrodes are placed on the opposite surfaces of the specimen. In the indirect method, the electrodes are positioned on the same surface of the prism: the transmitter electrode is fixed at a specific point and the receptor moves over the specimen, and at different distances, the transmission time is measured allowing for the velocity to be calculated.

In order to analyze the susceptibility to cracking of the mortars produced in this work, some parameters were calculated. The Center Scientifique et Technique du Bâtiment (CSTB) [15] refers to the dynamic modulus of elasticity and flexural strength ratio (E/σf) as indicators of the mortar's ability to resist cracking. This criterion is based on the fact that a lower dynamic modulus of elasticity provides a higher deformation capacity of the material, and a greater flexural strength induces the material to withstand tensions without cracking. Therefore, the tendency to crack due to restrained shrinkage is greater when the ratio between the modulus of elasticity and tensile strength is high.

Another parameter to evaluate the susceptibility to crack is based on the flexural and compressive strengths. The ductility of the material can be associated to this ratio (σf/σc) (i.e., the mortar is considered more ductile when this value is closer to 1). Ductility is a measure of the deformability of the material before fracture. Cracking resistance is correlated with the deformation capacity of the mortar and its ability to absorb stress without cracking [23].

The ability to absorb energy before fracture is correlated with the toughness of the mortar. The fracture toughness was calculated by the total area under the strain–stress curve of the results of flexural strength at 28 days.

Regardless of the binder used, all hardened mortars were cured as specified by EN 1015-11 [21]. The specimens were kept in molds for two days at a temperature of 20 ± 2 ◦C and a relative humidity of 95 ± 5%. After demolding, all specimens were maintained in the same conditions for a total of seven days. After that, the specimens were kept at 20 ± 2 ◦C and the relative humidity was reduced to 65 ± 5%, until testing.
