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?
- 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)
- 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
- 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.
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