Apparatus
| Item | Specification / Notes |
|---|---|
| Steel cylindrical measure | Internal diameter 115 mm, height 180 mm |
| Plunger / piston | Diameter 150 mm (for main apparatus) |
| Tamping rod | Diameter 16 mm (rounded end), length 450–600 mm |
| Balance | Capacity ≈ 3 kg with 0.01 g accuracy |
| Compressive testing machine | 40 tonnes capacity, uniform loading rate 4 tonnes/min |
| IS sieves | 12.5 mm, 10 mm, and 2.36 mm |
Sample Selection & Preparation
- Use aggregate passing 12.5 mm and retained on 10 mm IS sieve.
- Ensure the aggregates are surface-dry (no visible free moisture).
- Sample weight: as required by the cylinder capacity — record dry weight (W1).
Procedure (Step-by-step)
- Fill the cylindrical measure in three approximately equal layers.
- Tamp each layer 25 times using the rounded end of the tamping rod.
- After the third layer, level off the surface using the tamping rod as a straight edge.
- Insert the plunger carefully so it rests level on the sample surface.
- Place the cylinder & plunger assembly on the compression testing machine.
- Apply load at a uniform rate of 4 tonnes per minute until the total load reaches 40 tonnes, then release the load.
- Remove crushed material and sieve through a 2.36 mm IS sieve; collect fines that pass the sieve.
- Weigh the portion passing 2.36 mm (W2). Repeat the test on a second sample and record both W2 values.
Calculation
Aggregate Crushing Value (ACV) is the percentage ratio of crushed fines to the total sample weight.
Aggregate Crushing Value = (W2 / W1) × 100 Where: W1 = Total dry weight of sample W2 = Weight of material passing 2.36 mm IS sieve Report: Mean of two test results
Results & Reporting
Report the mean of the two test values as the final ACV for the aggregate sample. Include:
- Sample identification and date
- Apparatus used and calibration status
- W1 and W2 values for both trials and the mean ACV
- Any deviations from standard procedure
Acceptance Limits
| Application | Maximum ACV (%) |
|---|---|
| Cement concrete pavements | 30 |
| Wearing surfaces | 45 |
Frequently Asked Questions
Why do we use a 2.36 mm sieve for fines?
2.36 mm is the standard IS limit for defining crushed fines in this test — it provides a consistent basis to compare strength characteristics across aggregate sources.
What if my aggregate grading differs?
If grading is outside the specified range (12.5–10 mm) use a representative fraction or follow the standard practice for coarse/fine fractions as specified in the relevant code.
Notes & Best Practices
- Always run two trials and report the mean to reduce random error.
- Ensure the compression machine platen and the plunger are clean and parallel before applying load.
- Record ambient conditions and any visible degradation of sample during handling.
