Question

Consider the following statements regarding 'setting of cement':

1. Low-heat cement sets faster than OPC.

2. Final setting time decides the strength of cement.

3. Initial setting time of Portland PozzoIlona is 30 minutes.

4. Air-induced setting is observed when stored under damp conditions.

5. Addition of gypsum retards the setting time.

Which of the above statements are correct?
1. 1, 2 and 3
2. 2, 3 and 4
3. 3, 4 and 5
4. 2, 3 and 5

Answer 1

Correct Answer - Option 3 : 3, 4 and 5

Concept:

When water is added to cement, the ingredients of cement react chemically with water and form various complicated chemical compounds. The formation of these compounds is not simultaneous.

But setting action of cement of cement continuous for a long time. The mixing of cement and water results in a sticky cement paste and it goes on gradually thickening till it achieves rock-like state.

It is found that ordinary cement achieves about 70% of its final strength in 28 days and about 90% of its final strength in one year or so.

Low heat cement sets slower than OPC.

Final setting time does not decide the strength of cement.

Initial setting time of Portland PozzoIlona is 30 minutes.

Air-induced setting is observed when stored under damp conditions.

Calcium sulphate (CaSO₄): this ingredient is in the form of gypsum and its function is to increase the initial setting time of cement.

So here statement 3, 4 & 5 are correct.