## 4 Results and Discussion
### Push-Off Shear Tests
The values supplied by CM-2010 were adopted as reference values (100%). Two values of the experimental shear sliding were adopted for comparison: 0.5 mm and 2.5 mm. In the case of 0.5 mm of shear sliding, the Standards underestimate the contribution of the fibers to shear, highlighting the contribution of steel fibers, with values five times higher than those of the Standards. For 2.5 mm of shear sliding, polyolefin fiber reinforceents show higher values of shear strength than steel ones. This different behavior between steel and polyolefin fibers is due to their significant difference in the modulus of elasticity. In addition, the hook end of the steel generates a better behavior for minor sliding. In addition to the results analyzed previously, a detailed study was carried out regarding the cracking process in the push-off tests with the support of the video-extensometry technique. The time when cracking occured was different for the three types of concrete. Figure 11(a) shows the point of the first crack in the curve shear stress--crack sliding displacement (CSD). In the case of polyolefin fiber reinforced concrete, it coincided with the highest shear stress. In steel fiber reinforced concrete, the first crack appeared before this point. Figure 11(b) shows a specimen of SCCS70 at the time of cracking. In this figure the shear cracks are marked, placed in the ligament. Additionally, two bending fissures appear out of the resistant ligament. These bending fissures were previously analyzed by using a finite element model [35] and the specimens had to be reinforced externally for avoiding unexpected bending cracking in the cantilevers. Similar to tensile tests, the video-extensometry system allowed to observe the nucleation and growth of the cracks when they were imperceptible to the naked eye. As the tests progressed, the cracks in the ligament developed towards the tips of the notch, while the bending fissures were reduced, even becoming imperceptible. In some cases, the multi-cracking coalesced in a single fracture that connected the tips of the notch, while in other cases there was a multi-cracking pattern with cracks inclined to about 45\({}^{\circ}\) at the end of testing. Figure 12(a) shows a VCLP6 specimen at the end of the test, in which the cracking occurred with fissure directions of about 45\({}^{\circ}\), due to the reinforcement of only 6 kg/m\({}^{3}\) of polyolefin fibers. Figure 12(b) shows a VCCP10 specimen at the end of the test and it can be observed how the pattern and cracking are different, showing a single virtually vertical fissure that joined the tips of the notch. Lastly, Figure 12(c) shows the cracking pattern of a specimen reinforced with steel fibers. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Concrete Type** & **MC-2010** & **EHE-08** & \begin{tabular}{c} **CSD** \\ **2.5 mm** \\ \end{tabular} & \begin{tabular}{c} **CSD** \\ **0.5 mm** \\ \end{tabular} \\ \hline VCLP6 & \begin{tabular}{c} 100.00\% \\ (0.19) \\ \end{tabular} & \begin{tabular}{c} 92.98\% \\ (0.19) \\ \end{tabular} & \begin{tabular}{c} 74.94\% \\ (0.14) \\ \end{tabular} & \begin{tabular}{c} 200.33\% \\ (0.09) \\ \end{tabular} \\ VCCP10 & \begin{tabular}{c} 100.00\% \\ (0.11) \\ \end{tabular} & \begin{tabular}{c} 99.92\% \\ (0.11) \\ \end{tabular} & \begin{tabular}{c} 97.47\% \\ (0.07) \\ \end{tabular} & \begin{tabular}{c} 161.11\% \\ (0.01) \\ \end{tabular} \\ SCCS70 & \begin{tabular}{c} 100.00\% \\ (0.13) \\ \end{tabular} & \begin{tabular}{c} 132.37\% \\ (0.13) \\ \end{tabular} & \
\begin{tabular}{c} 60.56\% \\ (0.09) \\ \end{tabular} &
\begin{tabular}{c} 491.27\% \\ (0.04) \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Shear strength of fiber reinforced concrete: according to the Standards [8; 12] and experimental results, for 0.5 and 2.5 mm shear sliding (c.v. in parentheses). The cracking analysis of the push-off specimens was not focused only on the cracking patterns. In addition, the kinematics of the cracks was also studied with video-extensometry technique.