## 4 Results and Discussion
### Failure Type  
According to Figure 6, AE parameters AF and RA can be used to classify the failure modes of cracks formed in test beams. When the RA value is large and the AF value is small, the failure cracks mainly belong to shear cracks, which are generated by shear waves. On the contrary, when AF value is large and RA value is small, the cracks mainly belong to tensile cracks that are generated by tensile waves. Figure 13 shows the curves of RA and AF values of BFRPC beam and BFRPC-N beam with experimental duration. It can be seen from Figure 13 that the variation tendency of the RA values and AF values of the AE signals generated from BFRPC beam and BFRPC-N beam are almost the same, indicating that the cracks formed in both the test beams are composed of shear cracks and tensile cracks. Furthermore, in order to distinguish that the failure cracks formed in test beams belong to tensile or shear cracks more clearly, parameters \(\Phi\) is defined and calculated by Equation (3). \[\Phi=\left\{ \begin{array}{ll}\mathrm{RA-AF}>0,\text{ Shear cracks predominate}\\ \mathrm{RA-AF}<0,\text{ Tensile cracks predominate}\end{array} \right. \tag{3}\]  
\(\Phi>0\) indicates that the cracks that formed in the beams mostly belong to shear mode cracks. The larger the \(\Phi\) value is, the greater the damage caused by shear action. On the contrary, if \(\Phi<0\), cracks that formed in the beams belong to tensile mode cracks. The smaller the \(\Phi\) value is, the greater the damage caused by tensile action. In addition, the mutation of the \(\Phi\) value curve shows that failure mode changes within the beam. In order to analyze the proportion of these two kinds of crack modes more clearly, the percentage of the AE signals with the characteristics of \(\Phi>0\) or \(\Phi<0\) is also calculated in this paper. In addition, RPC beam, BFRPC beam, BFRPC-N beam and BFRPC-N-ID beam are selected to understand the influence of BF, notch, and interfacial damage on the beam failure cracks. \(\Phi\) value curves are shown in Figure 14, and all the curves can be divided into three stages by the same method discussed in Section 4.2. Figure 14c,d have no crack initiation stage due to the existence of notch, which is met well with the phenomenon in the bending test procedure. Figure 13: AE parameters RA and AF: (**a**) BFRPC beam; (**b**) BFRPC-N beam. It can be seen from Figure 14 that shear cracks of all RPC beams account for more than 80% of the total cracks, indicating that shear mode plays the dominant role in the beam failure process, which can infer that flexure strength of both RPC and BFRPC beam is such big that the possibility of tensile failure occurs is tiny during their service life in the actual engineering projects. Besides, as seen from Figure 14a,b, when the beam contains BF material, \(\Phi\) value of beam in the second stage has an obvious increasing tendency. The reason is that the bridging action from BF could transform the tensile mode cracks to shear mode cracks. Compared to the BFRPC beam in Figure 14b,c, the proportion of shear cracks in BFRPC-N beam reduces by 13% and the tensile cracks increases by 13%, indicating that notch causes more tensile failure of concrete, which is due to the stress concentration caused by the notch, which accelerates the rapid destruction of the material. This is also the main reason for the reduction of bending resistance caused by the notch. The notch is in the middle of the bottom of the beam. When the beam is subjected to bending load, the material at the notch of the beam will be subjected to more tensile action, which will lead to more tensile cracks. Moreover, as can be seen from Figure 14c,d, compared with BFRPC-N beam, the proportion of tensile mode cracks formed in the BFRPC-N-ID beam are reduced by 10%, and \(\Phi\) value decreases along with the experimental duration. It shows that the combined action of interfacial damage and notch further reduces the contribution of concrete materials properties to the bending resistance of the test beams.