HIGH ALUMINA CEMENT

HIGH ALUMINA CEMENT

High alumina cement is also known as aluminous cement or cement fondu . Its manufacture is entirely different from that of Portland cements. The raw materials are chalk and bauxite, the latter being a special clay of extremely high alumina content. The raw materials are mixed together dry, fed into special furnaces, and melted at an  extremely high temperature. The molten materials is cast into pigs, broken up, and then ground into cement without the addition of  any other material whatsoever. This is a much more expansive process than the manufacture of a Portland cement, but there are certain applications where the properties of high Alumina cement have advantage over other types. It producers concrete of far grater strength and in considerably less time  even than Rapid Hardening Portland cement, allowing earlier removel of form work. It is also more resistant to certain forms of chemical attack, such as that of sulphates, oils, and sugar juices. These properties make it attractive in spite of its great cost, when high strength are required at a very early age or when corrosive conditions are sufficiently severe.

               however, great care has to be taken in the use of High Alumina cement, It must not be mixed with any other type of cement , and has to be stored separately and handled by separate mixers, transporters and other equipment. The heat given off on setting is greater than with other cement, and the concrete is best not cast in thickness greater than 12 in. to 15 in. unless special precautions are taken. Nor should it be cast when its temperature on setting can rise about 80 ˚F. Thus it is inapplicable to work in tropical countries where the excessive temperature may have a deleterious influence on its strength. In view of the heat given off on setting , it is necessary in all application to strip formwork at a vary early stage and keep the concrete thoroughly saturated with water by continuous hosing for a period of at least 24 hours after placing. High Alumina cement should only be used strictly in accordance with the manufacturer's recommendation.

Quality of High Alumina cement

1./ Strength 

  Minimum requirements for mortar compressive strength are :

      6000 lb/sq.in. at 1 day;

       7000 lb/sq.in. at 3 days   and must show an increase on the 1-day test results

2./ Setting Time   

Initial setting time is to be not less than 2 hours and not more than 6 hours.

Final setting time is to be not more than 2 hours after the initial set.

3./ Fineness 

Minimum requirement of specific surface is 2250 sq.cm/gm

4./Soundness 

The opening  of the points in the Le Chatelier test is not to exceed 1.0 mm.

5./ Chemical composition 

   The total alumina content is not to be less than 32 per cent by weight of the whole. The ratio of the percentage by weight of alumina to the percentage by weight of lime is to be not less than 0.85 nor more than 1.3 .

       

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