# Size Effect on the Acoustic Emission Behavior of Textile-Reinforced Cement Composites
## 3 Results
### Effect of the Width of the Curved Elements on AE Behavior  
The analysis started with the beam with the smallest width in order to set the basic behavior and explanation relative to the fracture of the TRC before moving to the comparisons with the plate specimen. While the load was low, the AE was scarce. This corresponded to the elastic regime, where limited cracking was initiated. As the load increased, cracking became more frequent, and the AE rate increased, as can be seen in Figure 6a. Later on and before the final collapse, the cracking was continuous, as can be seen by the local fluctuations of the load curve, while at the end, the cumulative AE exhibited an almost vertical increase. At the same time, AE parameters like the rise time showed an increase with each successive stage (Figure 6b); before approximately 10 min, it was limited to 40 us, and later at approximately 12.5 min,  
Figure 5: Waveforms from sensors at different distances from pencil lead excitation on the TRC plate: (**a**) out-of-plane excitation and (**b**) in-plane excitation. The arrow in front of the plate denotes the direction of the excitation. The amplitude values of the second sensor are shifted downward for clarity. it reached 100 \(\upmu\)s, while at the final load drop and the macroscopic collapse, it expanded to values up to 200 \(\upmu\)s or higher, as is shown in Figure 6b. This increase in the values of the RT was interpreted as the shift occurred from matrix cracks to delaminations and fiber pull-out as the specimen was led to final failure [5,6]. It must be noted here that theoretically, it is also possible that several sources were acting simultaneously or in an overlapping manner at the moments of high intensity fracturing phenomena at the end of loading. This could impact the recorded waveforms, increasing the RT and duration characteristics. Although this cannot be excluded, the pencil-lead break excitations discussed in Figure 5 show that, depending on the conditions, even a single source can be recorded with a high RT (e.g., in-plane excitation recorded at 200 mm distance depicted in Figure 5b), showing that these differences were connected to the actual mechanism and propagation conditions and not necessarily to the overlapping of different waveforms. The corresponding results for the plate are shown in Figure 7a. A similar observation about the increase of the AE rate can be made, while it is evident that at the transient load drops (marked by arrows in Figure 7a), which indicate cracking events, the AE exhibited vertical increases. Usually, these large cracking events are also escorted by delaminations and fiber pull-out events, something responsible for the higher values of the RT that are evident at those moments (see Figure 7b). In Figure 7b, it also becomes obvious that the RT values were expanding to 100 \(\upmu\)s from the start of the experiment, certainly higher than the 40 \(\upmu\)s limit for the beam. This is already an indication that the matrix cracks occurring at a low load corresponded to different AE signatures in beams and plates of the same material. In order to make a valid comparison, and because the time scales of the different tests were not similar, the AE activity in terms of the RT and AF was represented versus the number of hits. The initial population of hits belonged to the elastic regime, where the dominant expected expression of damage was matrix cracks. Therefore, the AE of the  
Figure 6: Load history with (**a**) cumulative hits and (**b**) rise times from a curved TRC beam 25 mm wide. Figure 7: Load history with (**a**) cumulative hits and (**b**) rise times from a curved TRC plate 300 mm wide. first 200 hits was reasonably attributed to cracking without much interference from other fracture modes. At the same time, the medium was relatively undamaged, allowing us to check the effect of the geometry itself without the distortion due to damage. Figure 8a shows the sliding average of the RT for the first 200 hits for all three specimens.