What is Calcium Aluminate Cement
Calcium Aluminate Cement is a hydraulic binder with normal setting and rapid hardening obtained by finely grinding the resulting product of the combustion mixture of limestone and bauxite.
Bauxite is a hydrated aluminum trioxide (Al2O3. NH2O) that contains impurities of silicon dioxide and iron trioxide. To obtain optimum properties aluminous cement ratio of limestone and bauxite is chosen depending on the composition of oxidized finished product:
Al2O3 = 35 … 50% / CaO = 35 … 45% / SiO3 = 4 … 15% / Fe2O3 = 5 … 15
Aluminous cement mineralogy clearly differs from that of Portland cement, depending on the composition of raw materials and their thermal treatment of combustion and cooling.
Mineralogical constituent of aluminous cement base is monocalcium aluminate CA CaO.Al2O3-entering proportion of 55 … 75%. It is characterized by fast drying / heat of hydration high / high mechanical resistance. Found in small amounts and other components mineralogical as: trialuminatate Pent calcium 5 CaO.3Al2O3 – C5A3 /, CaO monocalcium double aluminate. 2Al2O3 – CA2 / gehlenit 2CaO. Al2O3. SiO2 – C2AS and silicate bicalcicC2S.
Dicalcium silicate, due to its own properties (hydration slow / low hydration heat / low early strength, there are important technical properties of high alumina cement.
Calcium Aluminate Cement – The Function
When mixing with water aluminous cement hydration reactions take place and its mineralogical components hydrolysis to form calcium hidroaluminats low basicity, hidrosilicats with small amounts of calcium and aluminum hydroxide.
The main reaction is the monocalcium aluminate, which forms the first phase hidroaluminate monocalcium the equation:
CaO.Al2O3 + 10 H2O ———-> CaO. Al2O3. 10 H2O
Hidroaluminate monocalcium is unstable and is transformed by hydrolysis hidroaluminate bicalcic crystalline and gel hydrated aluminum trioxide according to the equation:
2 (as a. Al2O3. 10 H2O) ——> 2CaO. Al2O3 .8 H2O + Al2O3nH2O
But Hidroaluminatul bicalcic thus formed is stable up to a temperature of 30 * C. At a higher temperatures turn into cubic crystalline tricalcium hidroaluminate after equation:
3 (2CaO. Al2O3. 8 H2O) ——> 2 (Al2O3 3CaO. .6 H2O) + Al2O3. NH2O
This transformation occurs with a sharp decrease in volume, which causes crazing cement stone and decreases its mechanical resistance 50 up to 80%.
- To avoid these changes in rock structure cement, aluminous cement is used in the underwater and underground construction and permanent in cold climate regions.
Aluminous cement resists well the action of sulfur water / soft water / of the mineralized / a dilute acids / organic substances such as phenol, cresol, sugar esters used as plasticizers in polymers, and other. Instead, it is resistant to concentrated acids and alkalis. Because of its specific intended use of aluminous cement is limited.
It is used in high strength concrete and quick setting / the concrete in winter, provided that during operation the temperature should not exceed 30 * C. Also used in various work environments subjected to aggressive food, chemical, textile and getting fireproof concrete aggregate (chamotte / chrome / magnesite / calcite etc.) used in lining furnaces working at high temperatures of 1300 – 1600 * C.
In recent years public and the media are increasingly anxious over the possible adverse effects of aluminum on human health, especially on Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis. Also, there were complaints about the risk of infants fed with milk containing aluminum. So, this might be an asking question for using it!