Water–cement ratio law — what does concrete strength primarily depend on? According to the (Abrams) Water–Cement Ratio Law for workable, plastic concrete, which statement best describes the primary determinant of compressive strength?
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AIt depends primarily on the total water content alone, regardless of cement content.
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BIt depends primarily on aggregate grading and not on water or cement.
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CIt is essentially independent of water content for plastic mixes.
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DIt depends primarily on the water–cement ratio (weight of water / weight of cement).
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EIt depends only on the brand or quality grade of cement, not on proportions.
Answer
Correct Answer: It depends primarily on the water–cement ratio (weight of water / weight of cement).
Explanation
Introduction / Context:The classic Abrams Water–Cement Ratio Law states that, for workable plastic concrete made with given materials and proper curing, compressive strength is governed primarily by the ratio of water to cement by weight. This principle underpins mix design and quality control on site.
Given Data / Assumptions:
- Normal Portland-cement concrete (no special binders).
- Workable plastic mixes (not dry lean or ultra-fluid self-compacting) and proper curing.
- Other variables such as aggregate type and temperature are held within normal ranges.
Concept / Approach:Higher water–cement ratio (w/c) increases capillary porosity after hydration, reducing strength and durability. Lower w/c produces a denser paste and higher strength, provided the concrete is still workable and properly consolidated. Absolute water content or cement brand alone cannot reliably predict strength without considering the w/c ratio.
Step-by-Step Solution:
Identify the law: strength is a function of w/c for workable concrete.Evaluate alternatives: total water alone or cement grade alone cannot capture porosity formation.Conclude: the correct controlling parameter is the water–cement ratio.Verification / Alternative check:Empirical strength–w/c plots consistently show monotonic strength reduction as w/c increases for given materials and curing, confirming the law in practice.
Why Other Options Are Wrong:
- Total water alone ignores cement content and paste volume.
- Aggregate grading affects workability but not the fundamental strength–porosity relation like w/c does.
- Claiming independence from water is incorrect; water governs porosity via w/c.
- Cement brand/quality matters but does not override the dominant effect of w/c.
Common Pitfalls:Chasing higher slump by adding water instead of using admixtures; ignoring that very low w/c may hurt workability and consolidation if not properly managed.
Final Answer:It depends primarily on the water–cement ratio (weight of water / weight of cement).