**5. Conclusions**

This article presents a proposal for using the AE method to assess the condition of fiber–cement boards. The research was carried out on five groups of elements exposed to environmental and exceptional factors. During the three-point bending tests, AE signals were recorded, which were then grouped into four classes using the k-means algorithm. Based on the presented results, it was found that the indicated method can be successfully used to confirm or deny the presence, and to assess the condition of, reinforcing fibers in boards, which directly affect the strength parameters of these elements. The frequencies recorded before destruction were also traced for each sample. It has been noted that the frequency values are significantly different for samples with reinforcements, compared to

elements with fired or degraded fibers. Initial hypotheses were confirmed during microscopic studies using a scanning electron microscope.

The following specific conclusions were drawn on the basis of the tests performed:


**Author Contributions:** Conceptualization, A.A.-B. and A.K.; methodology, A.K.; software, A.A.-B.; validation, A.A.-B. and A.K.; formal analysis, A.A.-B.; investigation, A.A.-B.; resources, A.K.; data curation, A.A.-B.; writing—original draft preparation, A.A.-B.; writing—review and editing, A.K.; visualization, A.A.-B.; supervision, A.K.; project administration, A.A.-B.; funding acquisition, A.K. All authors have read and agreed to the published version of the manuscript.

**Funding:** The tests were implemented thanks to the financial support of the Kielce University of Technology within the framework of the statutory work No. 02.0.06.00/2.01.01.00.0000 SUBB. BKWB. 20.001.

**Conflicts of Interest:** The authors declare no conflict of interest.
