Compaction testing concepts (Proctor): Identify the correct statements about compaction curves, air-void lines, hammer specifications, and drop height, and choose the best combined answer.

Introduction / Context:
Laboratory compaction (Standard/Modified Proctor) establishes the relationship between dry density and water content to find the Optimum Moisture Content (OMC). Understanding the shape of the curve, the meaning of the air-voids line, and the standard hammer specifications is essential for correct interpretation.

Given Data / Assumptions:

• A: OMC corresponds to the peak of the dry density–water content curve.
• B: An air-void line shows combinations of water content and dry density for a constant percentage of air voids.
• C: Hammer weight stated as 25 kg (this is incorrect for standard tests).
• D: Standard Proctor drop height is 30.5 cm (305 mm).

Concept / Approach:
Standard Proctor uses a 2.5 kg rammer with 305 mm drop; Modified Proctor uses a 4.5 kg rammer with 457 mm drop. Therefore, 25 kg is not a standard Proctor hammer weight. The OMC definition and the concept of the air-void line are correct, and 30.5 cm drop matches Standard Proctor.

Step-by-Step Solution:

Verification / Alternative check:
Refer to standard specifications (e.g., ASTM D698 for Standard Proctor): rammer 2.5 kg, drop 305 mm; ASTM D1557 for Modified Proctor: rammer 4.5 kg, drop 457 mm.

Why Other Options Are Wrong:

• All A–D correct: false because C is incorrect.
• Other subsets exclude one or more correct statements (A, B, D), so they are incomplete.

Common Pitfalls:
Confusing Standard with Modified Proctor; or thinking the air-void line is the zero air-voids line—these are different concepts.

Final Answer:
Only A, B and D are correct