Workability of concrete is directly proportional to: (i) Time of transit (ii) Water-cement ratio (iii) Grading of aggregate (iv) Strength of concrete (v) Aggregate-cement ratio
Correct Answer: B. (ii) and (iii)
📚 Detailed Explanation: Workability Direct Proportionality
Why B (ii and iii only) is correct:
(i) Time of transit — NOT directly proportional: As time passes, cement undergoes initial hydration, consuming free water and increasing stiffness. Workability decreases with transit time, not increases.
(ii) Water-cement ratio — YES: More water = less friction = more fluid paste = higher workability. Direct proportionality.
(iii) Grading of aggregate — YES: Well-graded aggregate achieves maximum packing efficiency (less void space). With fewer large gaps, the same paste volume provides better coverage = better workability. Direct relationship.
(iv) Strength — NOT directly proportional: Higher w/c = higher workability but lower strength (Abrams' Law). Inverse relationship.
(v) A/C ratio — generally inverse: Higher aggregate content = more surface area = more water needed to maintain the same workability.
(i) Time of transit — NOT directly proportional: As time passes, cement undergoes initial hydration, consuming free water and increasing stiffness. Workability decreases with transit time, not increases.
(ii) Water-cement ratio — YES: More water = less friction = more fluid paste = higher workability. Direct proportionality.
(iii) Grading of aggregate — YES: Well-graded aggregate achieves maximum packing efficiency (less void space). With fewer large gaps, the same paste volume provides better coverage = better workability. Direct relationship.
(iv) Strength — NOT directly proportional: Higher w/c = higher workability but lower strength (Abrams' Law). Inverse relationship.
(v) A/C ratio — generally inverse: Higher aggregate content = more surface area = more water needed to maintain the same workability.
Workability Relationships Summary
| Factor | Relationship to Workability |
|---|---|
| (i) Transit time | Inverse (workability drops over time) |
| (ii) Water-cement ratio | Direct (more w/c = more workable) |
| (iii) Grading of aggregate | Direct (better grading = better workability) |
| (iv) Strength | Inverse (high workability = low strength) |
| (v) A/C ratio | Generally inverse |
- Only (ii) w/c ratio and (iii) grading of aggregate are directly proportional to workability.