Materials Lab

Methods for determination of aggregate crushing value (ACV)

(BS 812-110: 1990)

Prepared by:

Eng. Mohammed Mousa

The Islamic University of Gaza - IUG

Scope:

This Part of BS 812 describes a method for the determination of

the aggregate crushing value (ACV) which gives a relative

measure of the resistance of an aggregate to crushing under a

gradually applied compressive load. The method is applicable to

aggregates passing a 14.0 mm test sieve and retained on a 10.0

mm test sieve. For other size fractions, there is another

recommended method. The method is not suitable for testing

aggregates with an aggregate crushing value higher than 30, and

in such cases the method for ten per cent fines value described in

BS 812-111 is applicable.

Principle:

A test specimen is compacted in a standardized manner into a

steel cylinder fitted with a freely moving plunger. The specimen is

then subjected to a standard loading regime applied through the

plunger. This action crushes the aggregate to a degree which is

dependent on the crushing resistance of the material. This degree

is assessed by a sieving test on the crushed specimen and is

taken as a measure of the aggregate crushing value (ACV).

Apparatus:

- A compression testing machine.

- A steel cylinder (open-ended) of 15.4 cm internal diameter and

12.5 to 14 cm depth, with plunger and baseplate.

- A cylindrical metal measure of 11.5 cm diameter and 18 cm

depth.

- A tamping rod 16 mm diameter and 60 cm length with both

ends hemispherical.

- A balance of accuracy of 0.1% of the sample weight.

- A set of sieves.

- A well-ventilated oven, thermostatically controlled at a

temperature of 105 ± 5 °C

- A rubber mallet.

- A metal tray.

- A brush, with stiff bristles.

Figure 1: Aggregate crushing value test apparatus

Procedure:

1. Reduce the laboratory sample to produce a test portion of

sufficient mass to produce three test specimen of 14 mm to 10 mm

size fraction.

2. Thoroughly sieve the entire surface dry test portion on the 14

mm and 10 mm test sieves to remove the oversize and undersize

fractions. Divide the resulting 14 mm to 10 mm fraction to produce

three test specimens each of mass such that the depth of the

material in the cylinder is approximately 100 mm after tamping as

described later.

Note: The appropriate quantity of aggregate may be found

conveniently by filling the cylindrical measure in three layers of

approximately equal depth. Tamp each layer 25 times, from a

height of approximately 50 mm above the surface of the

aggregate, with the rounded end of the tamping rod. Level off

using the tamping rod as a straightedge.

3. Dry the test specimen by heating at a temperature of 105 ± 5

°C for a period of not more than 4 h. Cool to room temperature

and record the mass of material comprising the test specimens

before testing.

4. Place the cylinder of the test apparatus in position on the

baseplate and add the test specimen in three layers of

approximately equal depth, each layer being subjected to 25

strokes from the tamping rod distributed evenly over the surface

of the layer and dropping from a height approximately 50 mm

above the surface of the aggregate. Carefully level the surface of

the aggregate and insert the plunger so that it rests horizontally

on this surface. Take care to ensure that the plunger does not jam

in the cylinder.

5. Place the apparatus with the test specimen and plunger in

position, between the platens of the testing machine and load it at

as a uniform rate as a possible so that the required force of 400

kN is reached in 10 minutes ± 30 s.

6. Release the load and remove the crushed material by holding

the cylinder over a clean tray known mass and hammering on the

outside of the cylinder with the rubber mallet until the particles

are sufficiently distributed to enable the mass of the specimen to

fall freely on the tray.

7. Transfer any particles adhering to the inside of the cylinder, to

the baseplate and the underside of the plunger, to the tray by

means of a stiff bristle brush. Weigh the tray and the aggregate

and determine the mass of aggregate used (W1) to the nearest

gram.

8. Sieve the hole of the test specimen in the tray on the 2.36 mm

test sieve until no further significant amount passes during a

further period of 1 min. Weigh and record the masses of the

fractions passing and retained on the sieve to the nearest gram

(W2 and W3 respectively). If the total mass of the two individual

fractions (W2 + W3) differs from the initial mass (W1) by more than

10 g, discard the result and repeat the complete procedure using a

new test specimen.

Note: Mechanical sieving should only be used for aggregates

which do not degrade under its action.

Calculation and expression of results:

Aggregate Crushing Value (ACV) = 𝑾𝟐

𝑾𝟏 × 𝟏𝟎𝟎

Calculate the mean of the two results to the nearest whole

number. Report the mean as the aggregate crushing value, unless

the individual results differ by more than 0.07 times the mean

value. In this case repeat the test on two further specimens,

calculate the median of the four results to the nearest whole

number, and report the median as the aggregate crushing value.

Note: The median of four results is calculated by excluding the

highest and the lowest result and calculating the mean of the two

middle results.

Note: The material to be tested should pass 14.0 mm sieve and

retained on 10.0 mm sieve (single size). When this size is not

available, other sizes as listed below may be used.

Table 1: Particulars of test sieves for testing other size fractions of aggregates

Sieve size for separating fines (mm)

Aggregate size (mm)

Retained on Passing from

5 20 28

3.35 14 20

2.36 10 14

1.70 6.3 10

1.18 5 6.3

0.850 3.35 5

0.600 2.36 3.35