Civil Engineering Reference
In-Depth Information
be well ventilated. Sulphur burns at 245°C, and large quantities of sulphur diox-
ide are emitted. Under normal circumstances there is very little risk of the mate-
rial igniting.
Silicate dust
This is removed from smoke when ferro-silica and silica, used in steel alloys and
the chemical industry, are produced. Silica dust, also called micro silica, is main-
ly composed of spherical glass particles. It does not react with lime and is a very
good form of concrete reinforcement. It can, for example, replace asbestos. Silica
dust is relatively new on the market, but is already used in products such as ther-
mal light concrete blocks, concrete roof tiles and fibre cement tiles.
Blast furnace slag
This is produced in large quantities at works where iron ore is the main raw
material. The slag is basically the remains of the ore, lime and coke from the fur-
naces. This is considered to be a usable pozzolana and can be used in Portland
cement to bulk it out.
It is also possible to produce slagwool which can be used as thermal insulation
in the same way as mineral and glasswool. The constituents of blast furnace slag
increase the level of radioactive radon in a building, but this is negligible.
Fly-ash
Fly-ash reacts strongly with lime and is used as an ingredient in Portland cement
and in the brick industry. It is a waste product from power stations that use fos-
sil fuels. It contains small amounts of poisonous beryllium and easily soluble sul-
phates which can seep into and pollute a ground water system when they are
dumped. Fly ash from waste-burning processes should not be used because it
will probably contain heavy metals.
Fossil meal
Oil refineries that use oil from porous rock formations on the sea bed will pro-
duce fossil meal as a by-product. This can be used as thermal improvement for
mortars and is also a good pozzolana.
