Lime MCQ with answer and solution

Concept

Setting properties and classification of hydraulic lime

Formula

Hydraulic setting: 2CaO·SiO2 + H2O -> C-S-H gel

Step-by-step solution

1. Underwater construction requires a binding material that hardens without atmospheric carbon dioxide. 2. Hydraulic lime contains clay impurities that react with calcium oxide to form insoluble calcium silicates and aluminates under water. 3. Fat lime only hardens via carbonation from air, while quicklime reacts violently with water. Answer: B

Explanation

Hydraulic lime contains 10% to 30% clay (silica and alumina), which enables it to set and harden under water or in damp, unventilated conditions through chemical hydration. Fat lime hardens only by absorbing carbon dioxide from atmospheric air and cannot set under water. Therefore, hydraulic lime is the correct choice for underwater or damp construction, making option B correct.

Why the other options are wrong

A) Fat lime hardens only through atmospheric carbonation and slakes without setting under water. C) Quicklime is unslaked calcium oxide (CaO) that slakes exothermically upon water contact. D) Slaked lime without clay content cannot harden under damp or submerged conditions.

Shortcut

Hydraulic lime = Hydrates under water; Fat lime = Requires atmospheric air to carbonate.

Common mistake

Selecting fat lime, which never hardens under water due to absence of atmospheric carbon dioxide.