## 6 Conclusions  
In this study, the feasibility of applying the microwave infrared thermography method (MIRT) to identify flaws in a CFRP reinforcement in the form of a lack of adhesive between the reinforcement and the concrete was examined. The most challenging element considered in the study involves using a sample that underwent an extended aging period of 10 years, which facilitated the development of natural deterioration in the reinforcement characterized by the fraying of the material at the edges and the chipping of the epoxy. Numerical models were used for comparison research and to ascertain the influence of the flaws related to material deterioration associated with aging on the efficacy of the MIRT, and they were validated through experimental verification. For this purpose, four numerical models with four variants of the sample were prepared: a sample without any defects; a sample with a defect in the form of lack of adhesive (central defect sample); a sample with defects simulating the aging of the material, located on the edges of the composite reinforcement layer (ageing defects sample); and a sample with defects simulating aging and with a centrally located defect in the form of lack of adhesive (central and ageing defects sample). A stochastic structure consisting of many cylindrical air spaces that spanned both the epoxy adhesive layer and the adjacent carbon composite layer was used to represent the flaws associated with the ageing process. Figure 16: Comparison between the time–temperature characteristics for the mean values computed for the ROI for the numerical result (CADS) and experimental result (ROI, covering the defected area). Figure 15: The temperature differences computed between the mean values of ROI for the cases: (**a**) the difference between ADS and NDS; (**b**) the difference between CADS and CDS. The results show that the proposed MIRT enables the detection and quantification of the extent of aging deterioration. The presence of aging changes does not significantly affect the detection of a defect located in the center of the sample. The comparison between the matching numerical and experimental results demonstrates a high level of consistency, confirming the accuracy of the assumptions made in the developed numerical models. It is worth noting that the experimental results show slightly higher temperature values for defects associated with the sample aging process compared to the numerical results, which may be caused by the random distribution of defects that may not necessarily correlate with the scenario, and the depth of defects in the real object may be larger. Moreover, the temperature increase in the mentioned region could potentially be affected by wave reflections, which were not considered in the numerical model. These remarks may be the keys to improving the accuracy of the proposed models in future studies. The present study offers potential perspectives in terms of applying the MIRT method to investigate the durability of different types of composites and other new construction materials under various environmental conditions. Conceptualization, S.A.K. and B.S. ; methodology, S.A.K. and B.S. ; formal analysis, S.A.K. and B.S. ; investigation, S.A.K. and B.S. ; data curation, S.A.K. and B.S. ; writing original draft preparation, S.A.K. and B.S. ; writing--review and editing, S.A.K. and B.S. ; visualization, S.A.K. and B.S. ; supervision, D.D. and F.B. ; funding acquisition, B.S., D.D. and F.B. All authors have read and agreed to the published version of the manuscript. This research was partially funded by West Pomeranian University of Technology, Szczecin, Poland. Not applicable. The raw data supporting the conclusions of this article will be made available by the authors on request. The work presented in the paper is the outcome of the collaboration between three research team centers: The Active Thermography Laboratory in Poland; LGCgE (Laboratoire de Genie Civil et geo-Environnement); and ESTP-Grande ecole d'ingenieurs de la construction in France.