alumina cement
Aluminum cement differs significantly in its structure, chemical composition and setting process from the Portland cements family. The main factor causing the binding here is A2O3 alumina, and not CaO.
Above 70% the composition of the cement are calcium aluminates of various forms, the most numerous of these is CA – (CaO Al2O3) and in turn C5A3. This cement also contains a lot of iron (do 15% iron compounds with lime – C2AF i C2F).
The calcium silicate content is nothing more than a few percent. The main hydrate is C4AH13 in crystalline form and amorphous Al(OH)3. however, no Ca is formed(OH)2. hence the high corrosion resistance of this cement. Aluminum cement requires approx 30% more water than Portland cements. Due to its composition, this cement obtains the highest in relation to other cements:
• initial strength (do 60 MPa after 24 hours), which is approx. 85% final strength up to 80 MPa obtained after 14 days.
• degree of calorific value,
• resistance to sulphate environment, ammonia, magnesium and acid, and the alkaline environment,
• fire resistance.
Cement is obtained by grinding aluminum clinker, obtained by sintering a mixture of limestone and bauxite without adding gypsum. This cement is expensive and very difficult to use. Moisture and temperature regimes must be strictly adhered to throughout its maturation period.
The clay cement produced in Poland under the name Górkal is available in several varieties with different amounts of ingredients, and therefore various properties.
Although these cements are resistant to aggressive sulphate environments, to – taking into account their price and implementation difficulties – in practice, they are used rather only for the production of refractory and refractory concretes. The refractoriness of aluminum cements comes from here, that the binding is typical of ceramic products at high temperatures. They must not be mixed with other cements or admixtures without prior testing.