Civil Engineering Reference
In-Depth Information
Borax
Borax is extracted mainly from kernite which contains boron. Boracic acid is pro-
duced through a reaction with sulphuric acid. Sources of borax are relatively
common. Borax and boric acid are used as fungicide and fire retardants, in insu-
lation made of cellulose fibre and for timber impregnation. Boron substances are
slightly poisonous, but in larger concentrations they affect plants and fish in
freshwater.
Asbestos
This fibrous material was used as a reinforcement for ceramics as early as the
Stone Age. As a building material it was widely used during the middle of this
century and reached its peak around 1965. It has been used as reinforcement in
different types of concrete, plastic and plaster products, and as insulation. It has
became very clear that asbestos is carcinogenic. Products containing asbestos are
now banned in most European countries, and elsewhere their use has been min-
imized.
Non-metallic minerals in building
The basic materials for which non-metallic minerals are used are mineral binders
and glass.
Cements and limes
Cement is a collective name for mineral binders in powder form, which set to
become solid when mixed with water. Pure lime binders are not usually consid-
ered cements. The main difference is that lime solidifies when it reacts chemical-
ly with air, while cement reacts with water in a hydrating process. While lime is
a binder reacting in air, cement is a hydraulic binder which can also be used
under water.
For use within a building, a material should not take longer than seven days
to set, though this depends upon where the material is going to be used.
The cement most usually used in building is Portland cement, but there are
plenty of other cements that have been used through the ages. In many cases,
pure lime products can replace cement. The high energy consumption during
production of Portland cement and the functional advantages of alternatives
have recently led to experiments with alternative cements.
Cements can have three basic building functions: as render, mortar or concrete.
The consistency depends on the number and size of the constituents, whether
sand or stone, and the proportion of water and any additives.
