Water–cement ratio and workability: Identify the INCORRECT statement regarding concrete strength and handling

Introduction / Context:
Workability, water–cement ratio (w/c), and compaction quality jointly control concrete strength and durability. Misconceptions about “minimum w/c for workability” often lead to adding unnecessary water, compromising performance.

Given Data / Assumptions:

• Standard concrete constituents, conventional aggregates.
• Workability may be improved by admixtures and grading, not only by water.
• Mechanical vibration is available for compaction.

Concept / Approach:
(a) and (b) reflect the classic w/c–strength relationship: more water (for the same cement) reduces paste strength and increases porosity. (d) is true: better compaction reduces voids and raises strength. Statement (c) is incorrect as an absolute rule: low w/c mixes can be workable using plasticizers, optimized grading, and proper vibration; they do not inevitably cause honeycombing if placed correctly.

Step-by-Step Solution:
Assess (a): rich vs lean with excess water → rich mix stronger → correct.Assess (b): strength decreases with increasing w/c → correct.Assess (c): blanket claim that w/c < 0.45 is unworkable is false; admixtures and vibration enable placement → incorrect statement.Assess (d): mechanical vibration improves density → correct.

Verification / Alternative check:
Modern mixes frequently target w/c below 0.45 (even 0.30–0.40) with superplasticizers to achieve both workability and high strength.

Why Other Options Are Wrong:
Option (e) says none are incorrect, but (c) demonstrably is incorrect.

Common Pitfalls:
Adding water to “improve workability” instead of using admixtures; under-vibration leading to trapped air despite adequate slump.

Final Answer:
If the water–cement ratio is less than 0.45, the concrete is not workable and will produce honeycombing is the incorrect statement.