The mineralogical composition of cement
In combustion processes raw materials in the composition of existing oxides react with each other forming compounds mineralogical. The largest share are:
Tricalcium silicate (Alita) – 3CaOSiO2 – C3S;
Bicalcic silicate (Belita) – 2CaOSiO2 – C2S;
Feroaluminatul tetracalcium (celite I or brownmilleritul) – 4CaOAl2O3F2O3 – C4AF;
Tricalcium aluminate (celite II) – 3CaOAl2O3 – C3A.
Mineralogical composition of portland cement clinker may vary depending on the chemical composition of the raw materials and manufacturing technologies. European Standard SREN 197 / 1.2-2002 requires for portland clinker following requirements: – at least 2/3 of the total weight is made up of silicates (alite fucked +) – silicate cements; – The percentage relationship between the calcium oxide and silicon trioxide in the composition is greater than 2; – The percentage in mass of magnesium oxide is less than 5%. If portland cement clinker, mineralogical compounds can be found, usually, within the following percentages: – C3S 40 … 73%; – C2S 2 … 35%; – C3A 1 … 18%; – 2 … 20% C4AF; The main properties of the cement, related to the influence of mineralogical components are: the rate of hydration, heat of hydration, mechanical resistance and evolution of resistance to chemical aggression, the amount of chemically bound water, etc. Changes in the composition of the Portland cement clinker mineralogy, allows to obtain a wide range of cements with different properties conferred concrete, both fresh as well as hardened state. For these cements are defined strength classes: 32.5, 32.5, 42.5, 42.5, 52.5, 52.5 (N or R), where the figure (32.5, 42.5 and 52.5) is the class of compressive strength in N / mm2, N is the symbol for normal initial strength and the letter R is the symbol for high initial strength.