Water–cement ratio and concrete strength: identify the incorrect statement (choose one) about how changing w/c affects strength.
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AIncreasing the water–cement ratio decreases the strength of concrete.
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BDecreasing the water–cement ratio generally increases the strength (up to a practical limit).
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CFor a given mix and curing, there exists an optimum low water–cement ratio that maximizes strength without harming workability.
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DIf the water–cement ratio is increased significantly, concrete becomes more porous and its strength reduces.
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ENone of these.
Answer
Correct Answer: None of these.
Explanation
Introduction / Context:The water–cement (w/c) ratio is the single most influential parameter governing the strength and durability of fully compacted, properly cured concrete. Understanding its effect helps in mix design and quality control.
Given Data / Assumptions:
- Statements concern qualitative effect of changing w/c on strength.
- Normal, well-graded mixes with proper compaction and curing.
- No admixtures or special concretes unless implied.
Concept / Approach:According to classic relationships (e.g., Abram’s law), for a given cement and conditions, concrete strength decreases as w/c increases because higher water content leaves more capillary voids after hydration. Conversely, reducing w/c (with adequate compaction and workability provision) raises strength up to practical limits.
Step-by-Step Reasoning:
Evaluate (a): Increasing w/c decreases strength → correct.Evaluate (b): Decreasing w/c increases strength (to a limit) → correct.Evaluate (c): There is a practical lower bound (too low w/c harms workability/compaction), so an effective optimum exists → correct.Evaluate (d): Higher w/c increases porosity → lower strength → correct.Verification / Alternative check:Empirical strength–w/c curves show monotonic strength reduction with increasing w/c for properly compacted mixes. Practical mix design also recognizes workability limits at very low w/c.
Why Other Options Are Wrong:Since (a)–(d) are all correct qualitative statements, none are incorrect; therefore “None of these” is the only option that matches the prompt to “pick the incorrect statement.”
Common Pitfalls:Assuming strength always increases simply by adding more water; neglecting the role of compaction and curing; forgetting that too-low w/c without admixtures can reduce achieved strength due to poor compaction.
Final Answer:None of these.