3. Lightweight aggregates
Lightweight aggregates are minerals, natural rock
materials, rock-like products, and by-products of manufacturing
processes that are used as bulk fillers in
lightweight structural concrete, concrete building blocks,
precast structural units, road surfacing materials, plaster
aggregates, and insulating fill. Lightweight aggregates are
also used in architectural wall covers, suspended ceilings,
soil conditioners, and other agricultural uses. Lightweight
aggregates may be classified into four groups [6]
Natural lightweight aggregate materials which are prepared
by crushing and sizing natural rock materials, such
as pumice, scoria, tuff, breccia, and volcanic cinders.
Manufactured structural lightweight aggregates which
are prepared by preprocessing shale, clay, or slate in
rotary kilns or on traveling grate sintering machines.
Manufactured insulating ultra lightweight aggregates
which are prepared by preprocessing ground vermiculite,
perlite, and diatomite.
By-product lightweight aggregates which are prepared
by crushing and sizing foamed and granulated slag,
cinders, and coke breeze.
The first three types of lightweight aggregates are
produced from naturally occurring materials while the
fourth is produced as a by-product of iron and steel
production. Lightweight aggregates are distinguished from
other mineral aggregate materials by their lighter unit
weights.
Lava is a boiling melt which may contain air and gases,
and when it cools down, it freezes to a spongy porous mass.
In other words, it produces lightweight material that is
porous and reactive. This type of material is known as
volcanic aggregates are produced by mechanical handling
of lava, i.e., crushing, sieving, a grinding [7].
Lightweight aggregate is used not only for its lighter
weight but also for its superior sound abatement, fire
resistance, insulation and geotechnical properties. As a
strong and lower density material, lightweight aggregate is
used in precast concrete to reduce the load in high-rise
buildings. It is used in concrete blocks to reduce their
weight and increase worker productivity. Lightweight
aggregate systems are also used both naturally occurring
clays and waste materials as feedstock.