PHYSICAL REQUIREMENTS FOR PORTLAND CEMENT

 PHYSICAL REQUIREMENTS FOR PORTLAND CEMENT 

Indian Standards has issued certain requirements which need to be fulfilled, to ensure quality control of Portland cement. These requirements are based on certain tests:

• Fineness
• Setting time
• Soundness
• Heat of Hydration
• Compressive strength 

FINENESS: The amount of fineness determines, the rate of reaction of cement. So with that it makes the relation between fineness and rate, inversely proportional. Finer the grading, more is the rate of reaction and vice versa. Fineness of cement is determined using Blaine's Air Permeability method.

SETTING TIME: There are two setting times of cement

• initial setting time
• final setting time

Determination of these times involves the use of Vicat's test.

SOUNDNESS: Soundness refers to the ability of cement to maintain a constant volume. Cement having greater volume of lime and magnesia lead to cracking. This is known as unsound cement. Soundness is determined using Autoclave test.

HEAT OF HYDRATION: Cement, on coming in contact with water causes a chemical reaction. This reaction is called hydration and in this, tremendous amount of heat is generated. It needs to be ensured that the heat of hydration does not exceed a certain amount because it can develop cracks in concrete.

COMPRESSIVE STRENGTH: This property of cement is determined using Concrete Cube Test in which cubes of cement are tested for failure under a compression testing machine. This test is carried out for cement cured for 7 days and 28 days.