## 4 Results and Discussion
### AE Basic Parameter  
The changes in AE parameters can reflect the information about the concrete failure process. In order to select appropriate AE parameters to understand the influence of BF, notch and interfacial damage on the bending performance of RPC beam, the BFRPC beam was taken as an example, and the variation diagram of its load curve and AE basic parameters (cumulative energy, hits, cumulative counts, amplitude, and duration) with the loading time are drawn in Figure 10.  
As shown in Figure 10, at the time of 700 s, there is an obvious abrupt change in the load curve, which is caused by the tensile failure of the concrete at the bottom of the beam. At this point, the duration of AE parameter (shown in Figure 10e) suddenly increased. At 2500 s, the beam is damaged and the duration increased rapidly again, which indicates that duration of the AE parameter is consistent with the change of beam structure. Therefore, the loading process of the beam can be divided into three stages by the sudden increase of the duration. In the first stage, 0-700 s, the cumulative energy, hits, and cumulative counts of AE parameters are too small, so it can be ignored, and the amplitude is within the range of 40-60 dB. This phenomenon indicates that the BFRPC beam is in the early stage of loading, with fewer micro-cracks and a smaller number and strength of AE events. This stage belongs to the cracks initiation stage. Besides, in the second stage, 700-2500 s, the cumulative energy, hits and cumulative counts of AE parameters begin to increase and increasing rates of all these parameters are relatively stable. The amplitude also increases, and the range of this parameter is 40-80 dB. This phenomenon indicates that the cracks in BFRPC beam begin to expand, and this stage belongs to the unstable development stage of cracks. In addition, in the third stage, after 2500 s, cumulative energy, hits, and cumulative counts of AE parameters increase sharply. This indicates that the cracks expand rapidly, which leads to the failure of the beam. This stage belongs to the failure stage. The above three stages show that AE parameters could accurately reflect the damage degree of the RPC beam structure from the scale of micro-cracks and effectively judge the failure stage of the beam body. Next, the cumulative energy and amplitude parameters are selected to further study the influence of BF, notch, and interfacial damage on the bending performance of RPC beams. The AE cumulative energy and amplitude of RPC beam, BFRPC beam, BFRPC-N beam, and BFRPC-N-ID beam are selected for analysis. The cumulative energy and amplitude change curves with time are shown in Figures 11 and 12, respectively. Figure 10: Cont. Figure 11: Influence of different factors on AE cumulative energy: (**a**) BF; (**b**) notch and interfacial damage. Figure 10: Basic AE parameters of BFRPC beam: (**a**) Cumulative energy; (**b**) Hits; (**c**) Cumulative counts; (**d**) Amplitude; (**e**) Duration. As can be seen from Figure 11, after 700 s, the cumulative energy begins to increase. At that time, the beam stress enters the second stage and the cracks begin to expand, which is suitable for analyzing the influence of BF, notch, and interfacial damage on the bending performance of the beam. Figures 11a and 12a,b can reflect that the cumulative energy and amplitude of the BFRPC beam are greater than that of the RPC beam in the second stage. The reason is that BFFRC belongs to BF reinforced material. In the process of material cracking, both BF and concrete will be pulled to break. Compared to RPC, the AE signals in BFRPC not only generated from the broken concrete but also from the broken BF. In the third stage, the cumulative energy of the BFRPC beam is greater than that of the RPC beam, because the accumulated deformation energy of BF reaches the limited value that it can bear. BF is pulled out or fractures, and the potential energy absorbed through BF deformation is released instantly, generating more AE signals and causing a sharp increase in cumulative energy.