## 3 Results
### Aspects of the Specimens after Testing  
#### 3.2.1 Failure Modes and Crack Patterns  
For the tests at ambient temperature, the failure mode depended on the embedment depth: the 75 mm anchors experienced concrete cone failure, whereas the 125 mm experienced a combined concrete cone and pull-out failure at the concrete-mortar interface (Figure 7). This is coherent with the theory drawn from past observations that stipulates that the anchor fails by concrete cone failure when the embedment depth is between 3-d and 5-d (where d is the diameter of the anchor), whereas it fails by a mixed failure mode for greater embedment depths [1; 3]. However, for the mixed failure mode, the height of the concrete cone part in past investigations was about 2-d to 3-d, while in the present study, it was 78 mm on average with a standard deviation of 12%, which corresponds to almost 5-d. Unfortunately, potentially key data that may explain this inconsistency, such as the fracture properties of concrete or the bond strength of the mortars, were not given in the past investigations. Moreover, the mechanism of combined failure is still subject to uncertainties, since theories differ on the question of which of the two mechanisms (debonding or concrete cracking) occurs first. The only known distinction that can be cited here is the nature of the mortar, which was organic (epoxy based) in the past investigations and inorganic in the present investigation. For the tests with slow-rate heating, the typical crack patterns are presented in Figure 8. As can be seen, the anchors 75 mm deep underwent concrete cone failure, whereas the two anchors 125 mm deep (T125-1 and T125-2) experienced a combination of a concrete failure and pull-out failure. This difference suggests that the bond stress at the embedment  
Figure 6: Thermal profiles in concrete and mortar with ISO 834-1 fire conditions. depth exceeded the bond strength of the mortar for the 125 mm anchors, while it was not the case with the 75 mm anchors because the applied load was lower. In the T125-1 test, the concrete part was cone shaped with a height of 35 mm, while the rest of the anchors showed a pull-out failure at the concrete-mortar interface. Some radial cracks could be observed at the surface of concrete, but the specimen was not split. In the T125-2 test, the cone-shaped concrete part was not clearly observed, but instead, a horizontal crack crossed the slab in a plane parallel to the exposed face, at a depth of about 40 mm, and the layer of concrete thus formed was split into several portions after the peak load. The lower part of the anchor also underwent pull-out failure at the concrete-mortar interface. In the tests conducted with ISO 834-1 fire conditions, the crack patterns are shown in Figure 9. A clear concrete cone failure was obtained in the tests T125-ISO-30 and T125-ISO-60, whereas for T125-ISO-75, the crack pattern showed a combined failure, with a cone part over 60 mm of the depth and a debonding at the concrete-mortar interface over the remaining depth. It can be seen that in the case of clear concrete cone failure, the concrete cover was removed, leading to direct exposure of the rebar, which is particularly dangerous for a structure. It is also interesting to observe that T125-ISO-1 and T125-ISO-2 switched from a combined failure at ambient temperature to a pure concrete cone failure at high temperature. Knowing that at high temperature for those two anchors, the temperature of concrete near the embedded end was under 50 \({}^{\circ}\)C and did not exceed 100 \({}^{\circ}\)C at the mid-depth, one possible explanation for this change in failure mode is thus the contribution of the concrete near the exposed face, which was at considerably different temperatures under ambient conditions and under ISO 834-1 fire conditions. A possible hypothesis is that cone-shaped cracks may initiate at different depths, and at ambient temperature, the crack that started at the embedded end was not fully developed  
Figure 8: Crack patterns in slow-rate heating tests.