## 4 Results and Discussion

Table 3: Physical–mechanical properties of the slate selected to assess the impact of subarctic climatic conditions through seasonal cycles with a total length of four months. indicates the stone quality based on the ultrasonic velocity measurements before (V\({}_{\rm{pre}}\)) and after the aging (V\({}_{\rm{post}}\)). VRI was calculated as (V\({}_{\rm{post}}\)/V\({}_{\rm{pre}}\))\({}^{0.5}\). These VRI values indicate a \"very good\" QBM (Quality of Building Materials). A classification of \"very good\" means that, in terms of ultrasonic speed, the samples withstood the accelerated degradation test excellently, meaning that freeze-thaw decay mainly affected the external part of the specimens, leaving the core relatively intact. The compressive strength of the material, and the point load index, suffered a significant decrease from 175 \(\pm\) 13 MPa to 133 \(\pm\) 14 MPa and 13.1 \(\pm\) 3.1 MPa to 12.5 \(\pm\) 2.4 MPa (24 and 4.5% change, respectively). The difference between the decay determined by the two methods is intrinsically linked to the test specification: (i) the uniaxial compression test uses a load applied uniformly to the specimen (50 mm side), and all the bulk (interior and exterior) contributes in a much more effective way to strength. Moreover, there is a higher probability of finding a critical defect that causes rupture [58,59]. (ii) Conversely, in the point load test, the load is applied to one point (located in the central area of the specimen), and there is a lower contribution of the decayed external part of the sample. In this method, the results are expected to present a lower change after the accelerated degradation test. In a realistic situation, the achieved results will create a structural weakening. Over time outdoors, the stone decreases its compressive strength due to microfracturing caused by frost effect. Figure 5: Results of aging test and mechanical characterization: (**a**) cubic slate, 50 mm side—rupture after uniaxial compression test; (**b**) prismatic specimens, 15 \(\times\) 15 \(\times\) 25 mm—rupture after the determination of point load strength index; (**c**) prismatic slate specimens, 50 \(\times\) 50 \(\times\) 300 mm dimensions—rupture after flexure test; (**d**) slate specimens, 200 \(\times\) 200 \(\times\) 30 mm dimensions—rupture after the anchorage test. As seen in Figure 5a, the cubic specimens (tested for uniaxial compressive strength) broke according to fracturing systems consistently oriented about 45\({}^{\circ}\). In the point load test and in the flexure strength test (Figure 5b,c), the samples broke based on two fracturing systems, perpendicular and parallel to the load application. The flexural strength of the samples is again conditioned by the S1 fracturing system and by the slaty cleavage itself, considering that the prisms tested cannot be the same before and after the aging. During the application of the load, the sliding of the upper and lower portions occurs along these fractures. This behavior is like a car leaf spring. The fractures favor a ductile behavior of the specimen during the flexural test, probably increasing its flexural curvature but simultaneously reducing the flexural strength. In fact, flexural strength changed from an initial value of 30.4 \(\pm\) 9.2 to 14.9 \(\pm\) 3.8 MPa, reaching a total decrease of \(-\)50.9 % (Table 2). Fractures (S1) due to frost are once again responsible for the decrease in the anchorage strength. In this test, the load was in fact perpendicularly applied to the slaty cleavage planes and tends to widen the planes by increasing their opening (Figure 6a,c). The results showed a relevant change from the anchorage rupture load, from 3141 \(\pm\) 221 N in pre-test to 2420 \(\pm\) 275 N.  
The solar simulation in the FITOCLIMA climatic chamber resulted in no relevant change in color. Figure 7a shows rather constant trends of the parameters L, a and b, although characterized by normal fluctuations [60].