## 4 Experimental Program
### Materials and Methods
The actual dimensions of the cut slot (length and width) were recorded. * The 25 cm flat jack was inserted into the cut slot, while the slab was still subjected to the compressive force. * The distances between each pair of gage points (\"post-cut readings\") at 14 cm distance were recorded. * The pressure in the flat jack was incrementally increased holding the pressure steady at each step, and at each increment the distance between each pair of gage points was measured. * The test was stopped when the original gage distances at 4 MPa were restored, and the flat-jack pressure read on the manometer was recorded. The allowable average deviation from the original gage length was 1/20 th of the maximum initial deviation, \begin{table}
\begin{tabular}{c c c} \hline
**Sample** & **Test** & **Flat Jack** \\ \hline  & M1A & A \\
1 & M1B & B \\  & M2A & A \\ \hline
2 & M3A & A \\ \hline
3 & M4A & A \\  & M4B & B \\ \hline \end{tabular}
\end{table} 
Table 1: Flat-jack test layout. Figure 6: Pump with manometer connected to the inlet port of the flat jack. with no single deviation exceeding 1/10 th of the maximum deviation. However, as the reliability of glued reference points was not absolute, it was acceptable to reject one gage measurement out of the set of five if it was clearly no longer functional and giving irrational readings. * The valve of the flat jack was opened, and the pressure was released, bringing the device back to its initial configuration. * The sequence of operations was repeated using the gage points at 20 cm distance. * The load applied to the concrete slab was reduced until the 3 MPa stress level was achieved. A 5 min period was waited to allow the load to stabilize. * The distances between the pairs of gage points at 14 cm distance were recorded. * The pressure in the flat jack was incrementally increased holding the pressure steady at each step, and at each increment the distance between each pair of gage points was measured again, until the original gage distances at 3 MPa were restored within the allowable deviations. The flat-jack pressure was recorded. * The sequence of operations was repeated using the gage points at 20 cm distance. * The pressure in the flat jack was released, and the load applied to the concrete slab was reduced until the stress level of 2 MPa was achieved. * The same procedure described above was repeated for the 2 MPa level. According to the procedure, measurements were performed by the flat jack at the same location on the slab for each level of compressive stress. At the end of the tests, the 25 cm flat jack was removed. The concrete slab was then reloaded to 4 MPa, and the cut slot was enlarged to accommodate the 33 cm flat jack. The actual dimensions of the enlarged cut slot were recorded. The procedure then followed the same steps described above. The actual area of the slot was calculated based on the dimensions measured after each cut and used to calculate the correction factor \(K_{a}\) for each test (Table 2). It must be also mentioned that differently from applications in masonry, where steel shims are used to achieve a tight fit of the flat jack into the cut slot and bridge over any interior voids in the masonry, in the present study, no shims were used, and the flat jack was inserted with a small gap into the slot. The size of the gap affected the deformation of the pressurized jack and therefore must be considered in the calibration.