ABSTRACT
The chemical composition of Portland cement occupies an important place among the characteristics given in the data sheets provided by cement companies. As shown in Figure 4.1, this chemical composition is given in terms of oxide contents. Usually, these values represent average monthly values, sometimes given with an illusory precision of two digits after the decimal point. Figures 4.2 and 4.3 present the principal chemical elements usually found in Portland cements, with some important characteristics of these elements. In Table 4.1, it is seen that the CaO and SiO2 contents are much greater than other oxide contents. The average CaO content is about 65 per cent, which is about three times the SiO2 content. CaO and SiO2 contents, when added, represent more than 85 per cent of the chemical composition of Portland cement. The next highest oxide contents are Al2O3 and Fe2O3 which are usually lower than 8 per cent. The four oxides CaO, SiO2, Al2O3 and Fe2O3 represent what are usually called the main oxides (Lafuma 1965).
