Which of the following statements of Abraham Law for water to cement ratio is true?
Correct Answer: D. Compressive strength decreasing w/c Ratio increases
📚 Detailed Explanation: The Inverse Relationship in Abrams' Law
Abrams' (Abraham's) Law explicitly describes an inverse relationship between w/c ratio and compressive strength. This is a direct consequence of how water affects the microstructure of hardened cement paste.
Why D is correct: As w/c increases: more water is present in the fresh mix → excess water beyond hydration needs creates capillary pores when it evaporates → higher porosity = lower density = lower compressive strength. Option A (directly proportional) is the opposite — incorrect. Option B (both increase) is also opposite of Abrams' Law. Option C (no effect) contradicts all experimental evidence.
Effect of Increasing W/C Ratio
| Effect | Direction |
|---|---|
| Workability | Increases ↑ |
| Bleeding | Increases ↑ |
| Capillary porosity | Increases ↑ |
| Compressive strength | Decreases ↓ |
| Permeability | Increases ↑ |
| Durability | Decreases ↓ |
Key Concepts for Students
- Higher w/c = higher workability + lower strength — the fundamental trade-off in concrete mix design.
- Every 0.05 increase in w/c ratio typically reduces 28-day compressive strength by about 3–5 MPa.
- Admixtures (plasticisers/superplasticisers) resolve the dilemma by improving workability WITHOUT increasing w/c.