Lime for underwater works — which type of lime is suitable for the construction of structures under water (e.g., foundations, harbors)? Select the best choice.

Introduction / Context:
Lime binders differ in their ability to set and harden in moist or submerged conditions. For underwater or constantly damp structures, the binder must develop strength by hydraulic reactions rather than only by atmospheric carbonation.

Given Data / Assumptions:

• Application: underwater or continuously wet environments.
• Types considered: hydraulic, fat/pure, and quick lime.
• Need: setting and hardening without access to air.

Concept / Approach:
Hydraulic lime contains clayey constituents that form hydraulic compounds (e.g., calcium silicates and aluminates) during burning. These compounds react with water to set and harden even in submerged conditions. Fat/pure lime requires carbon dioxide from air to carbonate and thus is unsuitable underwater. Quick lime is caustic and must be slaked; it is not a finished binder for underwater setting by itself.

Step-by-Step Solution:

Verification / Alternative check:
Traditional masonry practice and standards recommend hydraulic lime for wet foundations, retaining walls in damp soil, and underwater works.

Why Other Options Are Wrong:

• Fat/pure lime: Sets slowly in air; fails underwater.
• Quick lime: Must be slaked; not a hydraulic binder.
• None of these: Incorrect because hydraulic lime is suitable.

Common Pitfalls:
Assuming all limes behave similarly; the presence of clayey impurities during burning creates the essential hydraulicity.

Final Answer:
Hydraulic lime