Question

Consider the following statements;
High early strength of cement is obtained as a result of
1. fine grinding
2. decreasing the lime content
3. burning at higher temperatures
4. increasing the quantity of gypsum
which of these statements are correct?

• A. 1 and 2
• B. 1 and 3
• C. 2, 3 and 4
• D. 1, 3 and 4

Answer 1

The correct option is B 1 and 3

Gypsum is a retarder and prevents flash set. The rapid rate of development of strength is attributed to higher fineness and higher $C_{3}S$ and lower $C_{2}S$ content. Thus decreasing lime content will not result in rapid hardening or high early strength cement. The OPC has 63% CaO while rapid hardening cement has 64.5% CaO. A slight increase of CaO causes considerable increase in $C_{3}S$ converting the OPC to a rapid hardening cement. A slight decrease in CaO and increase in $Si{O}_2$ decreases considerably the proportion of $C_{3}S$ and increases proportion of $C_{2}S$ thus forming low heat cement.