Lime technology — fundamental definitions (calcination, setting, and product) Select the correct statement about lime manufacture and behavior:
-
AHeating a material to redness in contact with air is called calcination
-
BThe property by which lime hardens in damp places without free air is called setting
-
CThe solid product that remains after calcining limestone is called lime
-
DAll of the above
-
ENone of the above
Answer
Correct Answer: The solid product that remains after calcining limestone is called lime
Explanation
Introduction / Context:Civil engineers must distinguish basic lime processes and terms. Misuse of “calcination,” “setting,” and product names leads to confusion when specifying binders for mortar, plaster, and stabilization.
Given Data / Assumptions:
- Limestone mainly contains calcium carbonate.
- Calcination aims to produce quicklime by driving off carbon dioxide.
- Setting is a general term; hydraulicity is the specific ability to set under water or in damp conditions.
Concept / Approach:Calcination is thermal decomposition in limited or no air, not open oxidation in excess air. For limestone, the reaction is: CaCO3 → CaO + CO2 (on heating). The solid product CaO is quicklime, commonly referred to as lime (before slaking). The ability to harden in damp or underwater environments is termed hydraulicity, characteristic of hydraulic limes and cements, not simply “setting.”
Step-by-Step Solution:Identify correct definition: the residue after calcining limestone is lime (CaO).Correct a: heating to redness in contact with air is better termed roasting; calcination implies limited air and decomposition.Correct b: the property described is hydraulicity, not merely setting; all binders set, but hydraulic materials set without free air.Therefore, only statement (c) is correct.
Verification / Alternative check:Industrial lime kilns operate with controlled draft to achieve calcination; chemical analysis confirms loss of CO2 and formation of CaO.
Why Other Options Are Wrong:Option (a) confuses calcination with oxidation in free air.
Option (b) confuses a general setting phenomenon with hydraulicity.
“All of the above” is invalid because (a) and (b) are incorrect.
Common Pitfalls:Using lay terminology imprecisely; assuming any lime is hydraulic; overlooking that quicklime must be slaked before safe use in mortars.
Final Answer:The solid product that remains after calcining limestone is called lime