Civil Engineering Reference
In-Depth Information
Table 4.1:
The most common elements
Element
Chemical symbol
% of Earth's crust
Oxygen
O
49.4
Silicon
Si
25.8
Aluminium
Al
7.5
Iron
Fe
4.7
Calcium
Ca
3.4
Magnesium
Mg
1.9
Sodium
Na
2.6
Potassium
Ka
2.4
Hydrogen
H
0.9
Titanium
Ti
0.6
Total
99.2
have a shorter setting time. In a few chemical reactions with gases, air pressure
plays an important role - pressure decides the weight of the gases.
In chemistry there are also catalysts, which increase the rate of the reaction
without actually 'chemically' taking part in it. In an animal's digestion system
catalysts are known as vitamins and play a vital role in a whole series of process-
es.
A chemical reaction can in principle be reversed, and must be seen as a reac-
tion in equilibrium. Chemical compounds can be stable, metastable and unstable.
Life would not have been possible without metastable systems.
The different elements
Ninety-nine per cent of the Earth's crust consists of ten elements. The other 1 per
cent consists of, amongst other elements, carbon, which is a condition for bio-
logical processes.
There is a difference between organic and inorganic compounds. Carbon is the
basic element in all life, and is in all organic compounds even lifeless compounds,
such as oil and limestone, created from hundreds of decomposed organisms.
There are 500 000 carbon compounds. They include many compounds not
found in nature, e.g. plastics. Inorganic compounds number approximately
80 000.
Important factors in the physics of building materials
In every building project it is very important to have a clear picture of a materi-
al's physical properties. There are different demands on the different groups of
