Consider the following statements regarding the characteristics of good mortar : 1. The density and strength of mortars made of the same class of aggregate decrease as the proportion of fine aggregate is increased. 2. It requires about twice as much cement to produce a mortar of given strength when fine sand is used as it does with coarse sand. 3. Even small percentage of mica if present considerably increases the tensile strength and adversely affects the compressive strength. Which of the above statements are correct ?
- A1 and 2 onlyCorrect
- B2 and 3 only
- C1 and 3 only
- D1, 2 and 3
Solution
Concept
Effect of sand on mortar
Step-by-step solution
1. More fine aggregate means more voids and more water demand, which lowers density and strength (true). 2. Fine sand needs about twice the cement to achieve the same strength as coarse sand (true). 3. Mica is harmful: even a small percentage lowers strength, particularly tensile strength (so statement 3 is false).
Explanation
Coarse, clean, well-graded sand gives the best mortar. Mica flakes weaken the bond, so they reduce strength.
Why the other options are wrong
Statement 3 says mica increases tensile strength, which is the opposite of its real effect.
Shortcut
Fine sand = more cement; mica = harmful.
Common mistake
Accepting that mica helps.
Correct answer: A) 1 and 2 only