Source: http://www.ensh.dz/files/cours/1011/Mat%C3%A9riaux%20de%20construction/Chapitre%20I%20%3B%20G%C3%A9n%C3%A9ralit%C3%A9s%3B%20propri%C3%A9t%C3%A9s%20des%20mat%C3%A9riaux.pdf