# Some Key Aspects in the Mechanics of Stress Transfer Between SRG and Masony
## 2 Materials and Methods  
### Materials  
Masonry blocks were constructed with solid fired-clay bricks and a nominally low strength mortar for the joints. Nominal dimensions of bricks were 250 mm (length) \(\times\) 55 mm (width) \(\times\) 120 mm (depth). The compressive and tensile strength of bricks were evaluated on cylinders of nominal dimensions 50 mm (diameter) \(\times\) 50 mm (length) cored from the bricks. In total, twenty cylinders were cored: seven cylinders were used to evaluate the tensile strength (\(f_{bt}\)), while the remaining thirteen were used to evaluate the compressive strength (\(f_{bc}\)) of the bricks. The average value of tensile strength, compressive strength, elastic modulus, and fracture energy (which will be introduced later) of bricks are reported here along with the corresponding coefficient of variation CoV (within parenthesis), which represents a measure of the variability of the results. The tensile strength of bricks was obtained by means of splitting tests, and the average was equal to 3.16 MPa (CoV = 0.12). The average brick compressive strength, evaluated according to CEN EN 772-1 [34], was equal to 20.3 MPa (CoV = 0.17). Among those cylinders used for compression, five were instrumented with two strain gauges applied 180\({}^{\circ}\) apart along the circumference of the specimen to measure the elastic modulus (\(E_{b}\)) of bricks. \(E_{b}\) was evaluated on the stress-versus-strain curve obtained as the slope between 5% and 30% of the peak stress. The average elastic modulus \(E_{b}\) obtained was 7.3 GPa (CoV = 0.29) [35]. The fracture energy of bricks (\(G_{F}\)) was evaluated by performing three-point bending tests on three notched bricks, as the area under the load-displacement curve divided by the area of the ligament [36; 37; 38]. The average value of \(G_{F}\) was equal to 29.5 N/m (CoV = 0.272) [39]. The compressive strength of mortar joints was evaluated from the compressive strength obtained from the double punch test on fourteen specimens, and the average was equal to 15.9 MPa [35; 40]. The SRG composite system used to strengthen the masonry blocks comprised high-strength galvanized steel fibers (cords) embedded in an inorganic mortar matrix. Each cord consisted of five filaments. Three out of the five filaments were straight, and the remaining two filaments were wrapped around the other three with a high torque angle. Cords were arranged in unidirectional sheets mounted on a glass fiber micromesh. The cross-sectional area of the steel cord was 0.538 mm\({}^{2}\), and the density of the steel fiber sheet was 670 g/m\({}^{2}\)[41]. The mechanical properties of fibers, provided by the manufacturer [41], are reported in Table 1.  
Two types of mortar were employed for the SRG matrix: a hydraulic lime-based mortar (LM) and a cement-based mortar (CM) matrix. The lime-based mortar matrix was a hydraulic natural lime mortar with fine particles used for structural rehabilitation of existing masonry structures. The flexural strength of this mortar was evaluated according to [42] at 28 days using prisms with nominal dimensions of 40 mm \(\times\) 40 mm \(\times\) 160 mm, and the average was equal to 5.0 MPa (CoV = 0.22). The corresponding compressive strength, obtained by compressive tests on the two prisms resulting from the flexural test [42], was equal to 12.3 MPa (CoV = 0.16). The fracture energy, evaluated by means of three-point bending tests [43] on notched beams of dimensions 300 mm (length) \(\times\) 70 mm (width) \(\times\) 70 mm (depth), was equal to 30.3 N/m (CoV = 0.22). The second matrix was a cement-based matrix used mainly for the restoration of concrete elements. The flexural strength, compressive strengths, and fracture