## 3 Levels of Examination of the Interphase Zone between the Overlay and Concrete Substrate
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Method Name** & **Basic Descriptors** & **Suitability** \\ \hline Pull-off & \(f_{\text{b}}\)—pull-off adhesion & 1, 2 \\ \hline Bending & Crack propagation & 1, 2 \\ \hline \multirow{4}{*}{Shear} & Bond strength, & \\  & \(\sigma_{\text{n}}\)—normal stress, & \\  & \(\tau_{\text{n}}\)—shear stress, & 1, 2 \\  & \(c\)—cohesion coefficient & \\ \hline Flexural & Bond strength & 1, 2 \\ \hline Direct tensile, & & \\ Splitting prism, & Bond strength & 2 \\ Bi-surface shear. & & \\ \hline Splitting tensile & \(f_{\text{r}}\)—tensile strength of the interface & 2 \\ \hline Sand patch & _SRI_—Surface Roughness Index & 2 \\ \hline Profilometry & \(R_{\text{p}}\)—\"peak-to-mean\" roughness, & \\  & \(R_{\text{z}}\)—mean peak-to-valley height & 2 \\ \hline \multirow{4}{*}{3D laser scanning} & _Sku_—kurtosis, & \\  & _Str_—texture aspect ratio, & \\  & _Sbi_—surface bearing index, & \\  & _Sci_—core fluid rentention index, & \\  & _Svi_—valley fluid retention index, & \\  & _Sca_—arithmetical mean height, & \\  & _Sq_—maximum pit height, & \\  & _Sp_—maximum peak height, & \\  & _Sdr_—developed interfacial area ratio, & \\  & _Sq_—root mean square height, & \\  & _Ssk_—skewness, & \\  & _Vmp_—peak material volume & \\ \hline \multirow{4}{*}{Impulse response} & \(K_{\text{d}}\)—dynamic stiffness, & \\  & \(M_{\text{p}}/N\)—mobility slope, & \\  & \(N_{\text{av}}\)—average mobility, & \\  & \(v\)—voids index & \\ \hline \multirow{2}{*}{Impact-echo} & \(A\)—amplitude of transmit dilatational stress wave, & \\  & \(f\)—the frequency of the dilatational stress wave & \\ \hline Infrared thermography & C\({}_{\text{T}}\)—thermal contrast & 1, 2 \\ \hline UPV 1 & \(t\)—time of the ultrasonic wave transiting & 2 \\ \hline AE 2 & Crack propagation & 2 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The suitability of the available research methods and the basic descriptors that were assessed to evaluate the interphase zone between an overlay and concrete substrate. The Proposed Methodology for the Evaluation of the Interphase Zone between the Overlay and Concrete Substrate  
Figure 4 presents the author's methodology of the evaluation of the interphase zone between the overlay and concrete substrate. As can be seen from Figure 4, delaminations (non-destructive evaluation) can be sought for the 1 st level using NDT methods. The value of \(f_{\text{b}}\) can be obtained from tests either by using the destructive pull-off method or NDT methods and the ANN. Based on the basis of investigating concrete surface morphology, which was specified in [4], 2 nd level studies should aim to evaluate the surface morphology of the concrete substrate. Particular attention should be paid to the influence of the adhesion between layers on the maximum size of aggregate grains in the substrate concrete [67], the degree of the development of the substrate surface and the degree of exposing the aggregate on the surface of this layer caused by different methods of its preparation. In turn, 3 rd level investigations should aim to describe the course and structure of the air pores in the concrete of the interphase zone with regard to the method of preparing the surface of the substrate and the effect of this contribution on the adhesion of the layers. These tests can be performed using X-ray computer microtomography. At this level of observation, the hardness of the concrete in the interphase zone can be assessed using the nanoindentation method. At the 4 th level of examination, the testing of concrete in the interphase zone between layers should be performed using the SEM. The analysis should include e.g., the examination of the chemical