## 3 Results and Discussion
### Failure Mode from AE Events  
The instability failure of CGCM results from the initiation, propagation, and coalescence of cracks during loading, with the distribution pattern of these cracks significantly influencing the material's fracture behavior [35]. Therefore, studying the crack patterns of CGCMs from a microscopic perspective is crucial for understanding their instability failure  
Figure 7: AE characteristics of concrete with different fillers: (**a**) D7 Re; (**b**) D7 CB; (**c**) D7 CF; (**d**) D7 SF. mechanism. Previous research has shown that different crack modes, such as tensile and shear cracks, produce distinct waveform characteristics during loading, allowing failure modes to be identified through AE signal analysis [32]. Crack modes can be differentiated using two key AE parameters: the average frequency (AF), defined as the number of counts over the signal duration (measured in kHz, see Figure 8), and the RA value, which is the ratio of rise time to the maximum amplitude of the waveform (measured in \(\upmu\)s/V) [36]. These parameters help characterize crack types, with tensile cracks exhibiting lower RA and higher AF values, while shear cracks display lower AF and higher RA values. Each AE event was classified as either a tensile or shear crack by calculating the AF/RA ratio, enabling a quantitative analysis of crack evolution across different loading stages. To analyze the failure modes of concrete reinforced with different fillers, the classification of cracks was performed using an oblique line based on the RA-AF characteristics (see Figure 9). When selecting the relative ratio of RA and AF, there is currently no definitive value [37]. According to the literature [38], a ratio of AF:RA = 50 kHz \(\times\) V/\(\upmu\)s was suggested as a boundary to classify crack types based on moment tensor analysis. In Figure 9, cracks are classified as tensile when the AF signal is lower than 50 RA, while shear cracks occur when the AF signal is higher than 50 RA. Additionally, cracks were counted separately for each stage of loading. Table 5 shows the proportion of shear and tensile cracks at different loading stages. It can be observed that shear cracks form during the initial stages, specifically stages I, II, and III. As the loading progresses, the proportion of shear cracks gradually decreases, while the proportion of tensile cracks increases. By stage IV, tensile cracks become the predominant mode of failure. [PERSON] et al. [13] reported similar findings, indicating that AE activity in the earlier stages is associated with micro-cracking in the matrix, which is the primary active mechanism at that point, whereas extensive matrix cracking and fiber pull-out occur during the main fracture. The fiber pull-out can increase tensile failure [32]. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Mix ID**} & \multicolumn{3}{c}{**Tensile Cracks**} & \multicolumn{5}{c}{**Shear Cracks**} \\  & **S1** & **S2** & **S3** & **S4** & **S1** & **S2** & **S3** & **S4** \\ \hline D7 Re & 13.63 & 14.34 & 20.42 & 81.36 & 86.37 & 85.66 & 79.58 & 18.64 \\ D7 CB & 12.89 & 21.98 & 27.67 & 67.93 & 87.11 & 78.02 & 72.33 & 32.07 \\ D7 CFs & 10.57 & 14.57 & 15.23 & 87.64 & 89.43 & 85.13 & 84.77 & 12.36 \\ D7 SFs & 21.51 & 26.94 & 32.88 & 77.53 & 78.49 & 73.06 & 67.12 & 22.47 \\ D14 Re & 14.16 & 15.04 & 33.95 & 78.37 & 85.84 & 84.96 & 66.05 & 21.63 \\ D14 CB & 10.47 & 14.91 & 17.29 & 84.96 & 89.53 & 85.09 & 82.71 & 15.04 \\ D14 CFs & 11.42 & 14.19 & 21.44 & 74.39 & 88.58 & 85.81 & 78.56 & 25.61 \\ D14 SFs & 8.86 & 11.81 & 22.32 & 80.15 & 91.14 Figure 9: _Cont_.