Question

Before testing setting time of cement, what should one test for?
1. Consistency
2. Fineness
3. Strength
4. Soundness

Answer 1

Correct Answer - Option 1 : Consistency

Concept:

Consistency of cement:

• The standard consistency of a cement paste is defined as that consistency which will permit the Vicat plunger to penetrate to a point 5 to 7mm from the bottom of the Vicat mould.

• Vicat's Apparatus is used to find out the consistency of cement.

Fineness of cement:

• The fineness of cement is a measure of the size of particles of cement and is expressed in terms of the specific surface area of cement. The fineness of cement is measured as the % weight retained on a 90µm IS sieve over the total weight of the sample.
• It is measured by using the sieve analysis test and air permeability test.

Characteristic strength:

• The characteristic strength is defined as the strength below which not more than five per cent of the test results are expected to fall.
• Concrete is graded on the basis of its characteristic compressive strength of 150 mm size cube at 28 days and expressed in N/mm2.
• The grades are designated by one letter M (for mix) and a number from 10 to 80 indicating the characteristic compressive strength (fck) in N/mm2.

Soundness of cement:

• The soundness of cement refers to the stability of the volume change in the process of setting and hardening. If the volume change is unstable after setting and hardening, the concrete structures will crack, which can affect the quality of buildings or even cause serious accidents, known as poor dimensional stability.

• Le-Chatelier method and autoclave method are used to find the soundness of the cement.

Setting time of cement:

• There are mainly two types of setting time, initial setting time and final setting time.
• For ordinary portland cement, initial setting time = 30 minutes and final setting time = 10 hours

Explanation:

Before testing the setting time of cement, We should test for consistency of cement because water added to find the setting time is 85% of total standard consistency.