# Acoustic Emission Analysis of Fracture and Size Effect in Cementitious Mortars
## 5 Conclusions  
The effect of sample size and boundary condition on strength and fracture progress of cementitious mortar samples was investigated in Brazilian splitting tests. Size effects were analyzed and explained by means of AE analysis, and the following conclusions were drawn:  
1. Tensile splitting strength computed with EN 12390-6 [27] was found to be dependent on the load-bearing strip width. This tensile splitting strength changed by 25% and 72% for the medium and the small samples, respectively, as strip width varied. The increase in the strip width caused the failure load to increase and the maximum stress to decrease. EN 12390-6 [27] disregards the role of this strip in stress reduction, resulting in an overestimated tensile splitting strength. However, when using equations that properly account for the boundary condition, the variation of tensile splitting strength with strip width is reduced to 11% and 9% for the medium and the small samples, respectively. 2. The size effect was investigated on samples with varying sizes but similar boundary conditions (strip width). It was observed that, similar to [PERSON] et al. [24] and [PERSON] et al. [8], the larger sample gave the lowest tensile splitting strength, giving 14% lower tensile splitting strength than the small sample. The manner of fracture energy dissipation was identified as the cause for this effect. The smaller sample had the highest standard deviation. Hence, there was no significant difference between small and medium samples. In addition, the larger samples failed explosively (by making a loud noise), while the failure in the smaller samples was hardly noticeable, indicating the failure becoming more brittle as the sample size increases. 3. The AE hit count and the AE amplitude evolution for samples with different sizes were investigated. It was found that for larger samples, there was a lack of AE activity before approaching the peak load. In addition, near the peak load, there were more high-amplitude AE events for the larger samples compared to the other samples. This shows that as sample size increases, less distributed micro-cracks form before macro-crack propagation, and the macro-fracture is more brittle. 4. The AE source location plots at subsequent loading stages indicated the unsymmetric nature of crack propagation in the Brazilian splitting test. It also showed that the amplitude of the localized events increases with sample size. In addition, it was observed that there are hardly any located AE events in the post-peak period for the larger samples. This was explained by the more brittle failure as the sample size increases. 5. The width of the fracture process zone (FPZ) was calculated from located AE events and was found to correlate to the sample size. The size of the FPZ was found to increase with sample size, which is in agreement with the literature. In addition, it was noticed that the growth rate in FPZ was slower than the sample size increase rate. The wider FPZ indicates the higher amount of fracturing energy consumed by the larger sample. 6. Fracture analysis through \(b\)-value analysis was affected by the sensor-source distance. It was found that \(b\)-value analysis of AE hits detected by sensors close to the cracking region resulted in a better interpretation of the fracturing phenomena. This was due to signal amplitude attenuation. The \(b\)-value analysis revealed that for the larger samples, there is a short period of pre-peak micro-cracking and sudden macro-cracking at peak load. On the other hand, the macro-crack formation occurs at the post-peak period for the smaller samples. Again, this is an indication of the ductile to brittle failure transition that occurs when sample size increases. The research validated the impact of boundary conditions on the tensile splitting strength and was able to explain the occurrence and causes of size effect phenomena through advanced AE analysis.