Page 60 - New Trends in Eco efficient and Recycled Concrete

36 New Trends in Eco-efficient and Recycled Concrete

size distribution, diffraction X-ray, water absorption capacity, density and thermo-
gravimetric analysis.
Particle size distribution presents clear differences between BFA and BBA.
Usually BFA has a maximum nominal size around 200 μm and presents a distribu-
tion similar to coal FA, as these ashes are also obtained in filters. Fig. 2.6 shows
the particle size distribution of three types of BFA from the calcination of forest
residues (Berra et al., 2015).
Particle size distribution of BBA are used to present more differences than in the
case of BFA. Fig. 2.7 summarises the size distribution of different BBA. In these
cases, maximum nominal sizes between 2 and 9 mm were obtained (Modolo et al.,
2015; Cabrera et al., 2014), 4 mm being the medium maximum nominal size in this
type of BA.
With respect to X-ray powder diffraction (XRD), we can find different patterns
between BFA and BBA. Fig. 2.8 includes several XRD patterns obtained by Berra
et al. (2015) and Vassilev et al. (2013b). The XRD patterns of BFA did not reveal
the presence of highly water-soluble crystalline phases, such as halite (NaCl) or syl-
vite (KCl). In some samples, it is possible to be identified as a crystalline sulphate
phase (BFA-7) (Berra et al., 2015).
In general, with XRD patterns it is possible to observe newly formed amorphous
(non-glass) inorganic material. BFA present particles composed of non-fused phases
produced from different biomass varieties. BFA are mainly amorphous waste
because of their components from original biomass lose crystallisation in water at

300 1100 C, resulting in amorphisation (Vassilev et al., 2013b; Richaud et al.,
2004).
XRD patterns in BBA present differences with those based on BFA. Fig. 2.9
summarises the XRD patterns of BBA from olive plant trimmings (Sklivaniti et al.,
2017), olive cakes, olive trees and pines (Cabrera et al., 2014). Calcite is the main
constituent of the ash mass. The X-ray diffraction patterns of BBA reveals that

Figure 2.6 Particle size distribution of three BFA from the combustion of forest biomass
(Berra et al., 2015). BFA, Biomass fly ash.