Rice Hulls for Composites - Introduction to Polymeric Composites with Rice Hulls - page 62

with a Blaine number of 2,800-3,000 for concrete (i.e., it is finer than cement).
Silica is the basic component of sand, which is used with cement for plastering and
concreting. This fine silica from rice hulls provides very compact concrete. This ash is
also a very good thermal insulating material. The fineness of the ash also makes it a
very good material for sealing fine cracks in civil structures, in which it can penetrate
deeper than conventional cement-and-sand mixtures.
5.4.5 Production of Glass
The fact that rice hulls contain 20% opaline silica is significant in the manufacture
of glass because glass is composed primarily of silica. Heating rice hulls to high
temperatures will turn it into glass spheres. This opaline silica may be combined with
silicone dioxide (sand) to form a glass composite. This composite material can then
be used to produce all types of glass products. Some home-insulation products are
glass that has been blown into strands, and rice hulls would make excellent materials
for insulation. These glass spheres can also be used as filler in the manufacture of
plastic foams (e.g., flexible polyurethane foams).
5.4.6 Rice Hulls Ash in Road Building
Recycling of increasing volumes of plastic wastes, whether it is from domestic or
industrial activity, is a challenge with regard to environmental pollution. Although
there are many recycling programmes, one might say it is a 'losing battle' because of
the volumes produced. However, recently, a little-known town in India, faced with this
problem, came up with a unique way to deal with this. With little or no knowledge
of science or chemistry, they experimented using a combination of plastic wastes and
bitumen to discover a novel way to recycle plastic wastes so as to minimise pollution.
They have perfected a way of using this combination in road building.
The plastic waste is shredded into small pieces using a granulator or shredder and
then added into heated bitumen (≤60% by volume) and mixed thoroughly. The
high temperature melts the plastic easily. If this mixture is used on a road surface,
it gives a very smooth and flexible coating. According to reports, a road surface
made in this way does not crack, can bear high loads, and water seepage is minimal.
I suggest that addition of a small proportion of rice hull ash, which is rich in silica,
will greatly improve these properties. I recommend a basic combination of 40%
bitumen; 50% plastic waste; and 10% silica ash. The silica will blend easily and
give additional strength and form a surface coating to prevent rainwater absorption
and seepage.