## 4 Experimental Program
### First Series  
In this first series, only the criterion of report 11 [1] is applied: the comparison of the number and the size of the voids exposed on the drilled surface of the same core with those displayed in some figures contained in the report. In this case, Equation (6) of Section 3 was not applicable; in fact, in some cores, the unit weight of concrete was higher than that of the concrete acceptance testing. In particular, tests were carried out on cores extracted from two different structures assigned as second and third groups, respectively. The structures were designed with a concrete strength class of C25/30 (design strength class--DSC); the acceptance testing of hardened concrete was carried out according to the Italian code [29] and returned the strength classes shown in Tables 1 and 2 (indicated as actual strength classes (ASC) in column 12). Specifically, these are reinforced concrete (R.C.) tunnels and composite RC-steel bridges for which a legal dispute has arisen with reference on the mechanical properties of the concrete. Therefore, no further information can be provided at this time. All cores were carefully examined, prepared by grinding, and tested in compression using standard procedures. Compressive strength variability results were detailed in [12], where it was observed that (shown in Tables 1 and 2). * Second group: The percentage difference between two cores obtained from the same drilling varies from 0.05% to more than 18.50%, and the result obtained by varying the extraction point varies from 6.59% to 19.40%;
* Third group: The percentage difference between two cores obtained from the same drilling varies from 3.58% to more than 34.31%, and the result obtained by varying the extraction point varies from 2.42% to 27.65%. Experimental Results  
It should be pointed out that, even within the same drilling, significant variations in the percentage of voids can be recorded. These are sufficient to move the specimen from class 2 to class 4. As an example, the void assessment of a drilling of the second group is shown in Figure 1. In detail, from the drilling of 440 mm of depth with a diameter of 94 mm, 3 cores were obtained: MSC-1e, MSC-1f, and MSC-1g. The estimated void is equal to 3% for core MSC-1e (on the left of Figure 1), falling to 1.5% for core MSC-1f (in the centre) and decreasing further to 0.5% for core MSC-1g (on the right). These results are consistent with the variations in compressive strength of the same cores within the drilling indicated as Drilling n.3 in [2] (33.36 MPa, 36.28 MPa, and 40.13 MPa). This confirms that all these anomalies bring about not only a lack of homogeneity and variations in the grade of compactness and resistance in different sections of the structural element, but can cause variations in the resistance even within the same section. Figure 2 shows the assessment of voids obtained by varying the extraction point of the cores in the second group; it is easy to verify as the percentage of voids varies from 0.5% to 3.0%. Tables 3 and 4 report the potential strength estimation results obtained by using the Concrete Society technical report (CSTR), while Tables 5 and 6 show the results obtained using the proposed formation when the values suggested by the Concrete Society report 11 for the corrective factor CEV are adopted. Figure 1: Assessment of voids within the same drilling: (**a**) Specimen MSC-1e-V = 3%; (**b**) Specimen MSC-1f-V = 1.5%; (**c**) Specim MSC-1g-V = 0.5%. Figure 2: Assessment of voids for different points of core extraction: (**a**) V = 0%; (**b**) V = 0.5%; (**c**) V = 1.5%; (**d**) V = 3.0%.