Construction binders – source material for Plaster of Paris (POP) Plaster of Paris used for molding and plasterwork is obtained by calcining which raw material?

Introduction / Context:
Plaster of Paris (POP) is a fast-setting building material used for decorative molding, false ceilings, and patch repairs. Identifying its raw material helps engineers anticipate setting behavior, compatibility, and site handling requirements.

Given Data / Assumptions:

• POP is calcium sulfate hemihydrate.
• Calcination refers to controlled heating to remove chemically bound water.
• We choose the direct precursor mineral for POP manufacture.

Concept / Approach:

Gypsum is calcium sulfate dihydrate. On calcination at appropriate temperatures, it loses part of its water of crystallization to form the hemihydrate—Plaster of Paris. On rehydration with water at site, POP sets by re-forming dihydrate crystals. Other listed materials produce different binders (e.g., limestone → lime) and are not the direct source of POP.

Step-by-Step Solution:

Verification / Alternative check:

Manufacturing texts consistently describe POP production from gypsum via controlled calcination (usually 120–180°C depending on process).

Why Other Options Are Wrong:

Bauxite: Source of alumina, not POP.

Kankar / Limestone: Carbonate materials → lime on calcination, not sulfate hemihydrate.

None of these: Incorrect because gypsum is correct.

Common Pitfalls:

Confusing gypsum-based plasters with lime or cement-based plasters; overlooking the dehydration–rehydration setting mechanism.

Final Answer:

Gypsum