## 3 Results and Discussion
### Screeds Fresh and Hardened State Properties  
The binder to aggregate (b/a = 0.18) and the water to binder (w/b = 0.67) ratios were kept constant for all the prepared mixtures. The initial spread diameter was 100 mm for all the prepared compositions. The standard composition exhibited a final spread diameter of 109 mm. For the compositions in which 17 wt.% of OPC was replaced by BFA1, and for 50_BFA1_GS and 67_BFA1_GS, the values were slightly smaller (between 103 and 106 mm). All the other compositions fell apart (did not flow) after the 15 strokes. All the mixtures prepared with BFA2 also fell apart, with exception of the ones prepared with BFA2_GS that presented final spread diameter values between 101 and 105 mm, slightly smaller than the standard composition. [PERSON] et al. [21] and [PERSON] et al. [23] also verified that the spread diameter values decreased with the increase in OPC replacement by BFA. OPC substitution by as received and sieved BFA increased the water demand of the mixes. This tendency was reported by different authors [4; 18; 19; 23; 37]. BFA powders tend to retain water due to its irregular shape, size, and presence of organic matter [23], diminishing the mixture workability by reducing the amount of available kneading water. This leads to difficulties in the mixing process, increases the probability of pores occurrence and decreases the homogeneity and density of the samples [36]. These problems can be solved by adding plasticizers, not tried in the current study. All cured samples where OPC was replaced by as received or sieved BFA show higher water absorption values (are more porous) than the standard formulation (as will be discussed later). This result is partially caused by the poorer workability. The lower density of BFA (2.54 g/cm\({}^{3}\)[23]) when compared to that of OPC (3.15 g/cm\({}^{3}\)[38]) and the intrinsic porosity of the ash particles also contribute to the observed decrease in the density of the samples. Experimentally it was noted, for both ashes (BFA1 and BFA2), that the milling process decreases the water demand of the mortars, as confirmed by the obtained slump values. The same fact was reported by [PERSON] et al. [37]. This behaviour can be explained by the narrower particle size distribution (similar to the OPC), obtained after the referred pre-treatment (Table 2, Figures 1 and 2), and, as suggested by [PERSON] et al. [37], the grinding process disintegrated the irregularly shaped particles and the agglomerates. The mixing is facilitated, and a better homogenization of the mixtures is achieved, while the compactness of the mortars is enhanced. Characteristics approach the ones of the standard formulation, even when a higher OPC percentage is replaced (67 wt.%). The mass loss upon curing for the compositions prepared with BFA1 and BFA2 powders are presented in Figure 3. On the seventh day of curing, most of the compositions where OPC was substituted by BFA1 present a higher mass loss than the standard composition. The opposite behaviour was observed for the samples prepared with the BFA2. The mass loss occurs, essentially, until the 14 th curing day and the values are greater than the ones exhibited by the standard. The difference is bigger for the compositions prepared with BFA1 and the mass loss of the specimens tends to increase with BFA incorporation amount. This can be the result of the higher porosity and pore interconnectivity of these samples, as will be discussed later. Figure 4 shows the density of the prepared mortars cured for 28 days. The specimens in which 17 wt.% of OPC was replaced by BFA show densities close to the standard (maximum variation of <5%). The increase of OPC substitution from 17 to 67 wt.%, promoted a slight decrease (maximum variation < 10%). For the higher OPC substitution (67 wt.%), the specimens prepared with the sieved ashes have lower densities (1.77 g/cm\({}^{3}\) for BFA1 and 1.75 g/cm\({}^{3}\) BFA2) than the ones prepared with the ground and sieved ashes (1.85 g/cm\({}^{3}\) for BFA1 and 1.89 g/cm\({}^{3}\) for BFA2).