Difficulty: Easy
Correct Answer: Both (c) and (d)
Explanation:
Introduction / Context:
Set control is essential for practical placing and early strength development. Two commonly referenced additives are gypsum in cement clinker grinding and calcium chloride in concrete admixture practice. Understanding their roles prevents mis-specification and site delays.
Given Data / Assumptions:
Concept / Approach:
Gypsum (calcium sulphate) retards the flash set caused primarily by C3A by forming ettringite initially, thus giving workable time. Calcium chloride, by contrast, accelerates early hydration (especially of C3S), increasing early strength and reducing setting time; however, its use with steel reinforcement is restricted because chlorides promote corrosion unless strictly limited by codes.
Step-by-Step Solution:
Verification / Alternative check:
Specifications for OPC mandate a controlled SO3 content for proper set regulation; admixture datasheets list CaCl2 as an accelerator with limits or prohibition for reinforced concrete unless corrosion risks are addressed.
Why Other Options Are Wrong:
Options A and B reverse the functions; individually choosing C or D ignores that both statements are simultaneously true.
Common Pitfalls:
Using chloride accelerators with prestressed or galvanized steel; assuming gypsum increases strength—its primary role is set regulation.
Final Answer:
Both (c) and (d)
Discussion & Comments