2015 · Q20
Which of the following statements with regard to Portland cement are correct?
- 1Silica imparts strength to cement.
- 2Alumina makes the cement quick setting.
- 3Excess of lime increases the strength of cement.
- 4Calcium sulphate decreases the initial setting time of cement.
Select the correct answer using the code given below.
General KnowledgeChemistry
- A2 and 4 only
- B1 and 3
- C1, 2 and 4
- D1 and 2 only
Explanation
Silica (SiO2) imparts strength to cement and alumina (Al2O3) gives it quick-setting properties, so statements 1 and 2 are correct. However, excess lime causes unsoundness — expansion and cracking — rather than added strength, and calcium sulphate (gypsum) is deliberately added to retard, i.e., increase rather than decrease, the initial setting time. Hence 1 and 2 only.