Which of the following statement is INCORRECT?
Correct Answer: B. Graphically the relation between the strength of concrete and the water-cement ratio is approximately
📚 Detailed Explanation: Identifying the Incorrect Statement
This question tests careful understanding of the w/c ratio and its effects. Three of the four statements are factually correct; one contains an error about the graphical form of the strength-w/c relationship.
Why B is INCORRECT: Option (b) states the graphical relationship is “approximately [linear/direct]” — the statement appears cut off but implies a simple proportional relationship. In reality, Abrams' Law shows the strength-w/c graph is a hyperbolic (exponential) decreasing curve, not a straight line. The other options are correct: (a) Lower w/c = stiffer, less workable mix — correct; (c) Mechanical compaction achieves denser concrete at lower w/c than hand compaction — correct; (d) Lower w/c = higher strength per Abrams' Law — correct.
Strength vs. W/C Relationship Shape
| Claim | Correct? | Reason |
|---|---|---|
| Relationship is linear | INCORRECT | It is a hyperbolic curve (Abrams' Law) |
| Relationship is inverse | Correct | Higher w/c = lower strength |
| Relationship is exponential decay | Correct | f'c = A/B(w/c) |
Key Concepts for Students
- The strength-w/c graph is always a downward hyperbolic curve, never a straight line.
- Mechanical compaction (vibration) allows lower w/c ratios because it provides the energy to compact stiff mixes that hand compaction cannot achieve.
- Each IS exposure class specifies a maximum w/c, not a minimum, because lower is always better for strength and durability.