Cements: Quick-setting cement is produced by adding which of the following to the clinker or mix?

Introduction / Context:
Quick-setting cement is used where a rapid loss of plasticity is desired, such as in underwater works or leak stoppage. Its chemistry is tuned to hasten early reactions while controlling overall strength development.

Given Data / Assumptions:

• Ordinary Portland cement (OPC) typically contains gypsum to regulate setting.
• Aluminium sulphate is known to accelerate setting in cement systems.
• The target is quick setting, not necessarily high early strength alone.

Concept / Approach:
Adding small, controlled quantities of aluminium sulphate accelerates the hydration of aluminate phases, producing quick setting. Gypsum is often reduced to avoid excessive retardation. Pozzolana addition generally slows early set and is not used to make quick-setting cement.

Step-by-Step Solution:
Recognize accelerators: aluminium sulphate is a classic set accelerator.Regulate gypsum: quick-setting formulations reduce gypsum from normal OPC levels.Select option that captures both: option C reflects the common practice.

Verification / Alternative check:
Standards and references note aluminium sulphate as a setting accelerator; field mixes corroborate faster set times.

Why Other Options Are Wrong:
More gypsum increases retardation; less gypsum alone may not reliably give quick set without accelerator.Pozzolana typically slows early hydration; not a quick-setting agent.Finer grinding accelerates strength gain but is different from quick setting chemistry.

Common Pitfalls:
Confusing quick-setting with rapid-hardening cement; the latter is primarily about high early strength.

Final Answer:
Aluminium sulphate (very finely divided), often with reduced gypsum