Q.35 For cast in situ lining, identify the false statement.
- AIt is most resistant to erosion.
- BThe recurring maintenance charges are high.Correct
- CIt has a higher initial cost.
- DIt has a longer life than that of any other type.
Solution
Concept
Cast in situ concrete lining costs more at first but is strong, lasts long and needs very little maintenance.
Step-by-step solution
1. Cast in situ concrete lining is a hard, dense and continuous surface. 2. So it resists erosion very well. (A) is true. 3. Its first cost is high. (C) is true. 4. Its life is about 40-60 years, longer than other linings. (D) is true. 5. It needs very little repair, so recurring maintenance cost is low, not high. (B) is false.
Explanation
Cast in situ concrete lining is the best lining for strength, life and erosion resistance. Its main drawback is high initial cost. Its maintenance cost is very low, so the statement that maintenance charges are high is false.
Why the other options are wrong
A: True. Concrete lining resists erosion best. C: True. Initial cost is high because of material, labour and formwork. D: True. It has the longest life among common lining types.
Shortcut
Concrete lining means high first cost, low maintenance and long life.
Common mistake
Thinking a costly lining also has high running cost. In fact, maintenance cost is low.
Correct answer: B) The recurring maintenance charges are high.