In general ‘Cement’ means Gray Ordinary Portland Cement which is used for general purposes in construction. The cement is one of the most important raw materials used in building as the strength of any construction work depends on the quality cement. The gray cement should be factory-manufactured from a reputed manufacturer. It must not be from local plant manufacturer. It is properly packed from factory, not be hand packed locally. While taking supply of gray cement, manufacturing date, grade and type should be checked. The cement should not be more than six weeks old from the date of manufacturing.

Types of gray cement

• Ordinary Portland cement (for general use)
• Rapid-hardening Portland cement (where high early strength is required)
• Low heat Portland cement (in mass concrete for dam etc.)

Manufacturing of gray cement

All types of cement like Ordinary Portland Cement, Rapid-hardening Portland cement or Low heat Portland cement are manufactured by intimately mixing Calcareous, Argillaceous and Silica, Alumina or Iron Oxide bearing materials, which are burnt at clinkering temperature and are ground to produce gray cement, complying with specifications. No material except Gypsum or Water or both should be added after burning.

Specifications of gray cement

Fineness

There are following two methods to check fineness of Portland cement.

• Method 1: After sieving, the cement on IS test Sieve No.9 (B.S. Sieve No 170) should not      exceed 10% in case of Ordinary Portland Cement.
• Method 2: Specific surface by Air Permeability Method should not be less than 2150 sq. cm/  kg in case of Ordinary Portland Cement

Soundness

Alternatively autoclave expansion should not be more than 0.5% when tested according to IS 269 of 1989.

Setting time

Setting time of any type or any grade of cement when tested by Vicat apparatus method described in IS: 4031 should confirm following requirement.

• Initial setting time Not less than 30 minutes
• Final setting time: Not more than 600 minutes i.e. 10 hours

Compressive Strength

After 28 days compressive strength of cement concrete mix for various types of cement concrete mix is following.

Compressive strength of cement concrete mix