The Aggregate Crushing Value (ACV) test is a critical quality control method to assess the strength of coarse aggregates used in road construction and concrete production. This article explains the test procedure, calculations, and how to interpret results to ensure compliance with international standards like BS 812-110:1990 and ASTM C131/C131M-20.
What is the Aggregate Crushing Value Test?
The ACV test measures an aggregate’s resistance to crushing under gradually applied compressive loads. It determines:
- Suitability for high-stress applications (e.g., road base layers).
- Durability against mechanical degradation during transportation and compaction.
- Compliance with construction specifications (e.g., maximum ACV limits).
Equipment and Materials Required
- Steel Cylinder: 150 mm diameter with plunger and base plate.
- Compression Testing Machine: Capacity ≥400 kN.
- Sieves: 12.5 mm and 10 mm for sample preparation.
- Balance: Accuracy ±1 g.
- Oven: For drying aggregates at 105–110°C.
Step-by-Step Procedure
1. Sample Preparation
- Dry aggregates in an oven until constant weight.
- Sieve to retain particles between 12.5 mm and 10 mm.
- Fill the cylinder with 3 layers of aggregate, each tamped 25 times with a standard tamping rod.
2. Loading and Crushing
- Place the cylinder in the compression machine.
- Apply a 40-ton load at 4 tons/min.
- Hold the load for 10 minutes, then release.
3. Sieving and Weighing
- Remove crushed material and sieve through a 2.36 mm sieve.
- Weigh the retained fraction (W₁) and passing fraction (W₂).
Calculations and Interpretation
Aggregate Crushing Value Formula:ACV (%)=W2W1+W2×100\text{ACV (\%)} = \frac{W_2}{W_1 + W_2} \times 100ACV (%)=W1+W2W2×100
Acceptable Limits:
| Application | Maximum ACV |
|---|---|
| Road base (heavy traffic) | ≤30% |
| Concrete aggregates | ≤45% |
| Low-stress pavements | ≤50% |
A higher ACV indicates weaker aggregates prone to crushing.
Why Follow BS 812 and ASTM Standards?
- BS 812-110:1990: Specifies a 10-minute loading time and 40-ton load for consistency.
- ASTM C131/C131M-20: Uses a 12.5–9.5 mm aggregate size and different sieving criteria.
- Key Difference: ASTM requires a 2.36 mm sieve, while BS 812 uses a 2.36 mm sieve for fines.
Case Study: Improving Road Durability in Australia
A highway project in Queensland replaced aggregates with an ACV of 38% (failing BS 812) with stronger aggregates (ACV 25%). Result:
- 20% reduction in road surface cracks over 3 years.
- 15% lower maintenance costs due to reduced aggregate breakdown.
Common Errors to Avoid
- Inadequate Compaction: Under-tamping layers skews ACV results lower.
- Moisture Content: Wet aggregates falsely increase strength; always oven-dry samples.
- Overloading: Exceeding 40 tons overestimates aggregate weakness.
Tips for Accurate Testing
- Calibrate Equipment: Verify compression machine accuracy annually.
- Repeat Tests: Perform triplicate tests for consistency (discard outliers).
- Documentation: Record sieve sizes, load rates, and environmental conditions.
Conclusion
The Aggregate Crushing Value test is indispensable for selecting durable aggregates in civil engineering projects. Prioritize aggregates with ACV ≤30% for heavy-load applications and always adhere to regional standards. Regular testing during material sourcing prevents costly construction failures.
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