Quicklime (calcium oxide) in building works – behavior and uses Which statements about quicklime (CaO) are correct in civil engineering practice?

Introduction:
Quicklime (calcium oxide, CaO) is a foundational material in construction chemistry. Its hydration and carbonation reactions underpin uses such as mortar preparation, soil stabilization, and production of whitewash after slaking. The item checks multiple core behaviors of CaO relevant to site practice.

Given Data / Assumptions:

• Material: quicklime (CaO), not hydrated lime.
• Water addition refers to slaking carried out safely with adequate water and mixing control.
• Whitewashing refers to using the product of slaking (Ca(OH)2) as a coating.

Concept / Approach:

Two principal reactions define quicklime on site: (1) hydration to slaked lime (calcium hydroxide) with heat evolution, and (2) subsequent carbonation of hydroxide to calcium carbonate in air. Correct handling converts CaO into a usable binder or wash.

Step-by-Step Solution:

Verification / Alternative check:

Observed site practice shows vigorous heat release during slaking. Whitewash recipes begin with well-slaked lime. Over time, surfaces harden through carbonation, consistent with the chemistry above.

Why Other Options Are Wrong:

Each listed behavior (heat on hydration, reaction with CO2, production of slaked lime, suitability for whitewashing after slaking) is correct; thus the combined statement “All of the above” is true.

Common Pitfalls:

Confusing quicklime (CaO) with hydrated lime (Ca(OH)2), and attempting whitewashing with un-slaked CaO, which is unsafe and unsuitable. Proper slaking and aging improve workability and finish.

Final Answer:

All of the above