# Acoustic Emission Monitoring in Prestressed Concrete:
## 6 Conclusions
* Should ORMs on a structure be impracticable, the results of this research suggest assuming a minimum attenuation coefficient of 6 dB/m for the longitudinal direction of the bridges. * The observed scattering in the RSDs from rebound hammer measurements is less than that associated with wire breaks. This suggests that the boundary conditions inherent to wire breaks are naturally complex and result in a higher degree of variance. In contrast, the rebound hammer provides reproducible results, making it an appropriate testing or reference source for this application. * Attenuation behaviour exhibits pronounced frequency-dependent effects, with the attenuation coefficient approximately doubling on average from \(-4.7\) to \(-5.0\) dB/m in the 0-10 kHz frequency range to \(-10.3\) dB/m in the 40-50 kHz range. This pattern applies across both beams and bridges and for both types of signal sources. These results quantitatively align with those from other research, indicating a high level of consistency in the measured attenuation coefficients. Frequencies above 50 kHz experience significant attenuation within a distance of approximately 3 to 4 m from the source to the sensor and are largely negligible beyond this range. * The analysis of the directionality of attenuation across different structures reveals anisotropic behaviour, where transverse attenuation consistently exceeds longitudinal attenuation. This directional variance is influenced by structural specialities, such as voids and construction joints, as well as sensor orientation, with voids exerting the most significant effect. Notably, in precast concrete bridges with in situ-cast concrete slabs, evidence shows unrestricted signal transmission in the transverse direction across multiple prefabricated elements. In practical applications, the attenuation coefficients derived from rebound hammer tests offer crucial input for devising sensor layouts for the monitoring of prestressed concrete bridges vulnerable to stress corrosion cracking. The practice of stimulating the concrete surface and extending these findings to address the issue of wire break detection is justified. Nevertheless, it is recommended to incorporate an additional safety margin by applying a transfer factor. The results documented herein, in conjunction with reference [13], form an important basis for the development of models aimed at quantifying the probability of detection (PoD) for wire breaks in bridges. These models are to be elaborated and discussed in a forthcoming publication. Conceptualization, M.K. and S.M. ; methodology, M.K. ; software, M.K. ; validation, M.K. and S.M. ; formal analysis, M.K. ; investigation, M.K. ; resources, M.K. ; data curation, M.K. ; writing--original draft preparation, M.K. ; writing--review and editing, M.K. and S.M. ; visualization, M.K. ; supervision, S.M. ; project administration, S.M. ; funding acquisition, S.M. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Not applicable. Data Availability Statement: Data will be made available on request. The data are not publicly available due to privacy. The authors wish to express their gratitude to the municipal and state road authorities for granting permission to utilize the real-world measurement data collected from the bridges.