Civil Engineering Reference
In-Depth Information
Rice husk ash (RHA)
Rice husk, one the most abundant types of agricultural waste, has been
used for decades in construction. Worldwide production is estimated to be
140 Mt, 700 000 t of which are generated in Spain. Incinerating this husk
under controlled conditions (500-900 °C)( Fig. 5.5), which vary depending
on the source of the ash (laboratory or cogeneration), produces a practically
amorphous material (Copra, et al., 1981; Armesto et al., 2002), with different
morphologies (Borrachero et al., 2007).
RHA comprises mainly SiO
2
(85-90%), with much smaller K
2
O (2.5-5.5%),
na
2
O (0.1-1.2%) and P
2
o
5
(0.8-3.7%) contents. Its LOI ranges from 5 to
9%. Its reactive silica content is upward of 80% of the total silica in the
ash. RHA contains some crystalline compounds, which may differ with
the calcining temperature. At temperatures of over 800 °C (cogeneration),
reflection peaks typical of cristobalite, at 21.95°, 28.45° and 36.15° (2q),
are detected and the material is found to be practically amorphous. Quartz
and non-burnt coal may also be present.
Sugar cane ash (CSA)
The sugar cane industry generates two types of waste. The first, sugar cane
straw (SCS), is usually burnt in open landfills (or even on the plantation
itself) and practically unknown to the scientific community. Only Frías et
al. (2005, 2007) and Villar et al. (2008) have reported the potential of this
type of ash (SCSA) as an active addition. The second is sugar cane bagasse
(SCB), which is what remains after the juice has been extracted from the cane.
Research has focused on recycling this latter type of waste as an artificial
pozzolan. According to the data available, world cane production is in the
order of 1.5 billion tonnes, which translates into 375 Mt of bagasse and, once
5.5
Morphological aspect of the rice husk ash.
