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## What is the crushing value of aggregate?

The actual crushing value of an aggregate is a relative measure that shows the resistance to crushing under a slowly applied compressive load.

## Why do the Aggregate Crushing Value Test?

Aggregate crushing value test is done the find the actual crushing value of aggregate.

**We Need to carry out this test,**

- To find out how much resistance does the aggregate has against the surface abrasion under traffic.
- To find out how much resistance does the aggregate can withstand under the roller during construction.
- To determine the strength of coarse aggregate and suitability of the aggregate for construction.

## How to perform Aggregate crushing value test?

**Apparatus required**

- IS sieves of sizes 12.5 mm, 10.5 mm, and 2.36mm.
- Steel cylinder with open end and dimension of 15.2 cm internal diameter.
- A plunger that would fit the steel cylinder.
- Square base plate
- Measuring cylinder of dimensions: 11.5 cm internal diameter and 18 cm height.
- Steel tamping rod with one rounded end (diameter: 1.6cm and length 45 cm to 60 cm)
- Weighing Machine with accuracy 1 gm.
- Compression testing machine (Capacity: 1000 KN)
- Stopwatch

**Procedure**

- The aggregate sample is collected from the site.
- The sample is sieved. This can be done either manually or on a sieve shaker.
- The aggregate passing through 12.5 mm IS sieve and retained on 10 mm IS sieve is selected for a standard test.

- The sample is dried and allowed to cool to room temperature.
- 3 kg of dried sample is weighed.
- The measuring cylinder is filled with a dried sample in three layers of equal depth each.
- Each layer of the sample is given 25 no. of tamping with the rounded edge of the tamping rod.

- The top surface of the measuring cylinder filled with the three layers of the sample is then levelled with the help of the tamping rod.
- Now the sample is poured in a pan and total weight of aggregate required to fill the measuring cylinder is weighed and recorded as W1.
- These aggregates are then transferred to the test cylinder with the base plate as in the same manner it was filled in the measuring cylinder.
- The top surface is now levelled and the plunger is inserted to rest on the levelled surface.
- The test cylinder with sample and plunger is then placed in the Compression Testing Machine.

- The test cylinder is kept in such a way that the plunger just touches the loaded surface of the machine.
- Now, 40 tons of load is applied to the test cylinder in 10 minutes.

We know, 40 ton= 40000 kg= 400 KN

Therefore, 400 KN of the load should be applied.

The time(10 minutes) is started in the stopwatch.

- The crushed material is then transferred into the sieve of size 2.36 mm.
- Sieving is done now and the sample passing through the sieve is collected and weighed. The weight is recorded as W2.
- Aggregate Crushing Value (ACV) can be determined by using a simple formula:

- This test is repeated once or twice and the average crushing value of the aggregate is determined.
- The average crushing value in the different tests is the actual crushing value of aggregate.

**Important points to remember**

- It is recommended that the crushing value of aggregate should be less than 30%. If it is more than 30 % then 10% finer aggregate is suggested to use.
- The aggregate whose crushing value is less than 30% can be used for cement concrete road.
- The aggregate whose crushing value is less than 40% can be used for wearing surface.

This test must be done before it comes to road and pavement construction.

## Calculation Table for aggregate crushing value test

**Precaution**

- To prevent any sort of error due to the presence of moisture in aggregate, it should be heated to 100ºC – 110ºC and then properly cooled to room temperature before the test.
- The plunger should rest entirely on the aggregate without touching the test cylinder so that the entire load applied by the compression testing machine is passed into the aggregate only.
- The tampering should be done gently and evenly over the surface of the sample.
- The total weight of crushed aggregate passing through 2.36 mm sieve and retained on the sieve should not differ from the original weight of the sample by more than 1 gm.

I hope this Post remains helpful for you.

Happy Learning – Civil Concept

**Contributed By,**

**Sushmita Niraula**

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