## 3 Results and Discussion
### Freeze-Thaw Resistance  
The standard, 17_BFA1 and 17_BFA2 were subjected to freeze-thaw cycles. The values of density, water absorption and compressive strength of the specimens subjected to 0, 5, 15, and 25 consecutive freeze-thaw cycles together with the ones of a control sample (cured in normal conditions) are presented in Table 3. The compressive strength values increased for the samples subjected to the freeze-thaw cycles and for the control. However, the variation was stronger on specimens that underwent the cycles. This may mean that the hardening of the samples keeps going after 28 days of curing and that they benefit from contact with water during the immersion phase. After 28 days of curing, 17_BFA1 and 17_BFA2 samples have similar compressive strength values (\(\approx\)12 MPa); however, at the end of 25 cycles, 17_BFA2 exhibit higher (19.45 MPa) compressive strength than 17_BFA1 (16.44 MPa). This may indicate that given the BFA2 chemical composition (see Table 2), some hydraulic reactions have occurred during this period. The smaller particle size of BFA2, when compared to BFA1, is also beneficial for a higher reactivity. No significant variations on the density and water absorption values were observed for the three tested compositions (standard, 17_BFA1 and 17_BFA2) along with the durability tests. The water absorption values of 17_BFA1 and 17_BFA2 specimens remained always very close but higher than the standard. The density of the standard samples was always higher than that of the 17_BFA1 and 17_BFA2 samples.  
Figure 9: Effect of OPC content decrease on the compressive strength of screed mortars (cured for 28 days). Estimations assuming the strength declining simply based on the OPC amount decrease on the standard formulation are also represented (yellow circles and dotted line). The red line represents the minimum values required for the target application.  
Figure 10 shows photographs of the samples after 0, 5, 15, and 25 freeze-thaw cycles. Macroscopically, there was no surface degradation, and no detachments, efflorescence, or cracks were observed. The three studied compositions show to be resistance to 25 freeze-thaw cycles, therefore the substitution of 17 wt.% of OPC by BFA1 and BFA2 does not reduce their freeze-thaw resistance.  
[PERSON] et al. [17] also achieved good results for freeze-thaw resistance of BFA containing concretes. Specimens (75 mm \(\times\) 75 mm \(\times\) 350 mm), cured for 14 and 77 days, with 15-25 wt.% substitution of OPC (Type GU) by BFA resisted to 300 freeze-thaw cycles (temperature variation from \(-\)18 \({}^{\circ}\)C to 4 \({}^{\circ}\)C). This behaviour was attributed to the decreased permeability of the BFA containing compositions.  
The influence of other supplementary cementitious materials in a screed durability was reported by [PERSON] et al. [39]. These authors evaluated the effect of OPC (52.5 R) replacement (from 2.5 up to 50 wt.%) by ceramic powder, blast slag furnace and FA, in samples cured for 28 and 90 days, and subjected to 50 freeze-thaw cycles resistance. They concluded that the maximum incorporation amount is 12.5, 37.5 and 50 wt.% for ceramic powder, FA and blast furnace slag, respectively.