Aggregate crushing value test

Definition

The aggregate crushing value (ACV) is the percentage by weight of fines (passing the 2.36 mm IS sieve) produced when a sample of aggregate is crushed under a gradually applied load of 40 tonnes in a standard cylinder. It is a measure of the strength of the aggregate against crushing under a slowly applied (compressive) load (IS:2386 Part IV).

Apparatus

• Steel cylinder (mould) of 15.2 cm internal diameter with a base plate and a plunger (14.9 cm), and a tamping rod 16 mm in diameter and 45-60 cm long with a rounded end.
• Compression testing machine of 40 t capacity, IS sieves 12.5, 10 and 2.36 mm, balance (to 1 g), and a cylindrical measure 11.5 cm in diameter and 18 cm high.

Procedure

1. Take oven-dried aggregate passing the 12.5 mm and retained on the 10 mm IS sieve; fill the cylindrical measure in three layers, tamping each with 25 strokes, and strike off. Weigh the sample ($W_1$, about 3 kg).
2. Place the aggregate in the cylinder in three layers, each tamped 25 times, level the surface and insert the plunger.
3. Place the assembly in the compression testing machine and apply the load at a uniform rate so that 40 tonnes is reached in 10 minutes (4 t/min); then release it.
4. Remove the crushed material and sieve it through the 2.36 mm IS sieve; weigh the fraction passing ($W_2$) and the fraction retained.

$$\text{ACV} = \frac{W_2}{W_1}\times 100\%$$

The average of two tests is reported.

Significance and limits

• Low ACV = strong aggregate; high ACV = weak aggregate that crushes under load.
• Limits (IRC/NRS 2070): not more than 30% for wearing courses (bituminous surface, cement concrete) and not more than 45% for bituminous base and WBM base courses.
• Typical values: ACV below 10% is exceptionally strong, 10-20% strong, 20-30% satisfactory, above 35% weak.
• For aggregates with ACV above 30%, the ten per cent fines value is used instead.