## 3 Results and Discussion
### Screeds Fresh and Hardened State Properties
As pointed before, the milling process decreases the particle size (14.64 \(\upmu\)m for BFA1_GS and 9.30 \(\upmu\)m BFA2_GS; 21.95 \(\upmu\)m for BFA1_S and 17.71 \(\upmu\)m for BFA2_S--see Table 2), and also lead to a decrease in the amount of elongated particles, so a more homogeneous mixture and a higher compaction degree is achieved in the samples prepared with the milled and sieved BFA. This observation is in line with [PERSON] et al. (2017) that referred that a denser packing can be achieved by using a well-graded particle size distribution that allows smaller particles to fill the spaces between larger ones. Figure 3: Mass loss upon curing for the compositions prepared with: (**a**) BFA1 powders, and (**b**) BFA2 powders. Figure 5 present the water absorption of the specimens by immersion after 28 days of curing. For all the prepared compositions, the water absorption values are higher than for the standard formulation. The increase in the percentage of OPC substitution by BFA causes an increment in the water absorption values of the samples, as a result of their higher porosity. The negative effect of the utilization of BFA on the mortar's porosity was also previously reported by [PERSON] et al. [18]. The mass increase of the specimens with time, due to the water capillary absorption, is shown in Figure 6. The behaviour of samples with 17 wt.% of OPC substitution and the standard one is similar. However, the 17_BFA1_S and 17_BFA2_S samples exhibit a higher mass increase (after 90 min) than the respective standard sample (4.8 for BFA1, 3.9 for BFA2 and 1.9 wt.% for the standard). For the same percentage of OPC substitution, the mass increase is higher for samples prepared with sieved ashes (<63 \(\upmu\)m) than those containing ground and sieved wastes. The same behaviour was observed for the water absorption by immersion (Figure 5), meaning that their porosity is higher and is interconnected. Similar behaviour was observed for the samples in which 50 and 67 wt.% of OPC was substituted by BFA. The higher content of smaller particles, present in the ground and sieved fractions, can fill the capillary pores reducing the water sorptivity by capillary action. [PERSON] et al. [3] study the effect of partial OPC replacement with a milled mixture of  
Figure 4: Density of the mortars prepared with BFA1 and BFA2 after curing for 28 days. Figure 5: Water absorption of the mortars prepared with BFA1 and BFA2 powders after curing for 28 days. BFA and bottom bed ash (with a fineness similar to that of OPC) in the mortars average pore diameter. After a slight increase in the average pore diameter for 10 wt.% substitution, the authors verified that for 15 and 20 wt.%, the average pore diameter decreased. This finding was attributed to a partial filler effect of the ashes. Figures 7 and 8 show the values obtained for the compressive and flexural strength of the specimens cured for 28 days, respectively. The use of BFA1 and BFA2 (as received or pre-treated) as OPC substitute promote, in general, a deterioration of the mechanical properties. The same result was achieved by other authors [4; 6; 23; 24]. The mechanical resistance of the specimens prepared with the as-received ashes is as lower as higher is the ash amount, as reported in previous works [4; 6; 18; 23]. However, the decrease is much smaller for the lower (17 wt.% of OPC) than for the higher (50 wt.% of OPC) ash content. The incorporation of pre-treated ashes (sieved and grounded and sieved) did not affect so strongly the mechanical properties of the specimens. The samples in which 17 wt.% of the OPC was replaced by the pre-treated ashes have mechanical properties quite similar to the standard formulation. This behaviour is clearer for the specimens that incorporate BFA2, as they have higher density and lower water absorption values. The target application requires, as minimum values for flexural and compressive strength, 3 MPa and 10 MPa, respectively.