Cement Paste and Concrete – Fundamental statements about hydration and performance Which of the following statements correctly describe what happens as water–cement paste hardens and how cement contributes to concrete behavior?
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AWater–cement paste hardens due to hydration reactions.
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BDuring hardening, cement paste binds the aggregates together.
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CCement contributes strength, durability, and watertightness to concrete when properly proportioned and cured.
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DAll of the above
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ENone of the above
Answer
Correct Answer: All of the above
Explanation
Introduction / Context:Cement is the primary binder in conventional concrete. When mixed with water, a complex set of chemical reactions occurs, turning a plastic mixture into a hardened stone-like material. Understanding these fundamentals is necessary for proper mix design, placing, and curing practices that lead to durable structures.
Given Data / Assumptions:
- Ordinary Portland cement as the principal binder.
- Normal curing and proper water content for hydration.
- Aggregates are inert fillers contributing volume and skeleton, but not binding capacity.
Concept / Approach:
Hydration of cement produces compounds (for example, calcium silicate hydrates) that form the binding matrix. This matrix envelops and adheres to aggregate particles, creating a composite material. Proper paste quality, aggregate characteristics, and curing govern the resulting strength, durability, and watertightness. Poor curing or wrong proportions increase porosity and permeability, undermining performance.
Step-by-Step Solution:
Option A: Correct—hydration is the cause of setting and hardening; without water, hydration halts.Option B: Correct—the paste binds aggregate into a coherent mass; the interfacial transition zone quality is crucial.Option C: Correct—adequate binder content, low w/c ratio, and curing yield strong, durable, and relatively watertight concrete.Therefore, “All of the above” is the accurate selection.Verification / Alternative check:
Laboratory tests (compressive strength, permeability) consistently correlate improved curing and optimized w/c ratio with superior performance metrics, confirming these statements.
Why Other Options Are Wrong:
“None” contradicts basic cement chemistry; any single statement would be incomplete by itself in representing the full picture.
Common Pitfalls:
Assuming cement content alone determines quality; ignoring the decisive role of w/c ratio and curing; poor consolidation leading to honeycombing and leakage.
Final Answer:
All of the above