Page 58 - New Trends in Eco efficient and Recycled Concrete

34 New Trends in Eco-efficient and Recycled Concrete

manufacturing lightweight wall board and bricks with special properties.
Ferna ´ndez-Pereira et al. (2011) studied the possibility of applying 20% BFA by dry
weight to manufacture clay bricks, obtaining appropriate results. BFA was applica-
ble in all these cases depending on its properties and chemical composition.
Several studies on the application of BBA and BFA in concrete and mortar man-
ufacture have been carried out and concluded that they could be applied in the man-
ufacture of cement-based materials, limiting the degree of substitution of aggregate/
cement application.

2.2.2 Chemical composition of BA

In this section, we discuss the chemical properties of BFA and BBA. The chemical
properties of BFA and BBA depend on the biomass origin that is burned for obtain-
ing f electrical energy and on the technological process applied in the BTPP.
Vassilev et al. (2013a) studied the chemical composition of BFA, using 86 sam-
ples of this ash with eight varieties of biomass origin. Table 2.2 summarises the
oxide composition of these eight types of BFA.
Table 2.5 shows the main content of the ashes. It would be favourable to obtain
a high content of the sum of calcium oxide 1 silica oxide 1 aluminium oxide.
These three components should exceed 60% to obtain appropriate properties to be
applied in concrete and mortar manufacture. Higher quantities were obtained in
CaO 1 SiO 2 1 Al 2 O 3 in ash from beech wood chips (SiO 2 12.33, CaO 67.80,
Al 2 O 3 20.12), rice husks (SiO 2 94.38, CaO 0.97, Al 2 O 3 0.21) and switch-
grass (SiO 2 66.09, CaO 10.19, Al 2 O 3 2.21) (Vassilev et al., 2013a). These
three kinds of ash would be the best to use in the manufacture of concrete and
mortar.
BBA have been less studied and there are few works where a summary of the
chemical properties of this kind of ash is included. Hinojosa et al. (2014) published
a work entitled ‘Potential use of BBA as alternative construction material:
Conflictive chemical parameters according to technical regulations’, in which the

Table 2.2 Chemical properties of BFA samples (Vassilev et al., 2013a)
Characteristics Beech Corn Plum Rice Switchgrass Sunflower
wood cobs pits husks shells
chips

SiO 2 12.33 27.65 3.59 94.38 66.09 23.46
CaO 67.80 13.19 14.65 0.97 10.19 15.18
Al 2 O 3 0.12 2.49 0.11 0.21 2.21 8.67
Fe 2 O 3 1.09 1.55 0.68 0.22 1.36 7.27
K 2 O 2.59 35.49 44.88 2.29 9.62 28.29
MgO 11.43 2.05 11.62 0.19 4.70 7.27
P 2 O 5 2.29 2.49 20.12 0.54 3.91 7.07
SO 3 0.80 7.14 2.47 0.92 0.83 4.03