## 2 The Experimental Campaign
### Specim Geometry and Test Setup
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \multirow{2}{*}{**Specimen Designation** (\({}^{\text{th}}\))} & \multirow{2}{*}{\(p\) (\%), \(l_{\text{rank}}\)/d\({}_{\text{b}}\)} & \multirow{2}{*}{\(\sigma_{\text{Nept}}\) (**N/mm\({}^{2}\))**} & \multicolumn{2}{c}{**Mean Concrete Compressive Strength (MPs)**} & \multirow{2}{*}{\(\text{s}_{\text{*}}\) (**mm**)} & \multirow{2}{*}{\(\text{w}_{\text{m}}\) at s\({}_{\text{n}}\) (**mm**)} & \multirow{2}{*}{\(\text{w}_{\text{m}}\)/mm\({}^{2}\)} & \multirow{2}{*}{\(\text{w}_{\text{m}}\)/mm\({}^{2}\)} & \multirow{2}{*}{\(\text{Failure}\) (**N/mm\({}^{2}\))**} & \multirow{2}{*}{\(\text{Mode}\)} \\  & & & & & & & & & \\ \hline \multicolumn{11}{c}{**Block A**} & \multicolumn{11}{c}{**Block B**} \\ \multicolumn{11}{c}{} & \multicolumn{11}{c}{Specimens without external compressive stress} \\ \hline R-16/B/12/0.2 & 0.302, 12.5 & 0.00 & 36.00 & 15.94 & (1.50) * & (0.97) * & 0.85 & 1.02 & L.OC \\ R-31/B/20/0.1 & 0.302, 20.0 & 0.00 & 31.10 & 34.76 & 0.40 & 0.36 & 2.36 & 2.65 & 1 \\ R-26/B/6/0.1 & 0.302, 62.5 & 0.00 & 49.14 & 26.04 & 0.10 & 0.19 & 1.28 & 1.58 & L \\ R-21/B/B/20.1 & 0.302, 12.5 & 0.00 & 25.57 & 21.38 & 0.40 & 0.25 & 2.86 & 2.18 & L.OC \\ \hline R-25/E/6/0.1 & 0.679, 6.25 & 0.00 & 25.06 & 31.10 & 0.35 & 0.35 & 2.27 & 1.76 & I, MOCs \\ R-31/E/20/0.1 & 0.679, 20.0 & 0.00 & 31.10 & 34.76 & 0.80 & 0.44 & 3.53 & 3.91 & I, MOCs \\ R-21/E/21/0.1 & 0.679, 12.5 & 0.00 & 25.57 & 21.38 & 0.60 & 0.21 & 4.49 & 3.22 & I, MOCs \\ \hline R-16/C/6/0.1 & 1.206, 6.25 & 0.00 & 36.00 & 15.94 & 0.20 & 0.22 & 1.21 & 1.42 & I, MOCs \\ R-21/C/12/0.1 & 1.206, 12.5 & 0.00 & 39.74 & 20.98 & 0.55 & 0.37 & 1.81 & 2.90 & L.OC \\ \hline \end{tabular}
\end{table} 
Table 2: Main characteristics of specimens, experimental and calculated values of maximum shear. After casting each part, the specimens were covered with hessian cloth and were kept wet for 2 to 3 days. Testing was performed one to two months after the construction of block \"B\". Until then, the specimens were stored in the interior of the laboratory, in controlled environmental conditions. For the measurement of the compressive strength of concrete, conventional concrete cylinders (diameter/height = 2, diameter = 150 mm) were cast together with each concrete block, and they were tested in compression the day of testing the corresponding specimens (mean concrete compressive strength values are given in Table 2). As a matter of fact, the compressive strength and the overall properties of the concrete affect the behavior of the interface. In cases where the new concrete is governing the behavior of the interface (e.g., when the interface reinforcement is fully anchored into the old concrete, while the added concrete layer is thin, allowing for reduced activation of the interface reinforcement), the use of innovative types of concrete (see e.g., [27]) may contribute to improved interface behavior. However, this case is not examined within the current investigation and, thus, conventional concrete types and compressive strengths are used for the construction of the specimens. Furthermore, the case of deteriorated (e.g., due to environmental actions) existing concrete is not examined either. Besides the presence of a normal compressive stress on the interface, the embedment length of the bars in the specimens was among the parameters investigated (equal to 6.25, 12.5, or 20 times the bar diameter). In case of cast-in reinforcing bars, the embedment length was smaller than the anchorage length required for full development of the yield strength of the bars (according to Section 8 of Eurocode 2 [18]). The experimental results are presented for pairs of specimens differing only in the value of normal compressive stress \(\sigma_{\text{N,ext}}\) on the interface (either zero or 0.30-3.00 MPa, according to Table 2). Figure 2 shows the test setup [22; 28]. The MTS(r) actuator (\"M\") (maximum capacity = \(\pm\)300 kN) was placed vertically on a steel frame (\"F\").