the rules of aggregate crushing value test pdf

The Rules of Aggregate Crushing Value Test

The Aggregate Crushing Value (ACV) test is a fundamental method used to evaluate the resistance of coarse aggregates to crushing under gradually applied compressive load. This test is standardized by various organizations, including ASTM, BS, and IS, to ensure consistency in assessing material quality for construction purposes.

Objective

The primary objective of the ACV test is to determine the relative crushing resistance of aggregates under specified conditions. The results help in selecting suitable materials for road bases, sub-bases, and concrete mixes where strength and durability are critical.

Apparatus Required

1. Steel Cylinder: A cylindrical container of 150 mm internal diameter with a base plate and tamping rod.
2. Compression Testing Machine: Capable of applying a load of 400 kN at a uniform rate.
3. Balance: Accurate to 0.1 g for weighing aggregates.
4. Sieves: 12.5 mm and 10 mm IS sieves for grading the aggregates.
5. Tamping Rod: A 16 mm diameter rod with a rounded end for compacting the sample.

Test Procedure

1. Sample Preparation:

   • Dry the aggregate sample and sieve it through 12.5 mm and 10 mm sieves.
   • Take a portion of the material passing through the 12.5 mm sieve but retained on the 10 mm sieve.
   • Fill the steel cylinder in three layers, tamping each layer 25 times with the tamping rod.

2. Application of Load:

   • Place the cylinder in the compression testing machine and apply a load of 400 kN at a rate of 4 kN per second.
   • After crushing, remove the sample and sieve it through a 2.36 mm sieve.

3. Calculation of Aggregate Crushing Value:

   • Weigh the material passing the 2.36 mm sieve (W2) and the total weight of the sample (W1).

   • The ACV is calculated as:

     [
     ACV = \left( \frac{W2}{W1} \right) \times 100
     ]

Interpretation of Results

The ACV value indicates the percentage of fines generated after crushing. A lower ACV signifies stronger aggregates with higher resistance to crushing, making them suitable for high-stress applications.

• Acceptable Limits:
  • For high-quality base courses, the ACV should be ≤ 30%.
  • For sub-base materials, values up to 45% may be acceptable depending on regional standards.

Significance in Construction

The ACV test helps engineers select aggregates that ensure long-term stability in pavements and concrete structures. Poor-quality aggregates with high ACV values may lead to premature failure under traffic loads or environmental stresses.

Conclusion

The Aggregate Crushing Value test is a crucial quality control measure in construction projects. By adhering to standardized procedures, engineers can ensure the selection of durable aggregates that meet structural requirements.

(Sources: IS: 2386 (Part IV), BS 812-110, ASTM C131/C131M)