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Aggregate Crushing Value
Aggregate Crushing value is a relative resistance of aggregates to crushing under gradually applied compressive load.
The aggregate Crushing Value Test is an important test to be performed on aggregate. The strength of aggregate parent rock is determined by preparing cylindrical shape specimens of size 25 mm in diameter and 25 mm in height.
This cylinder is subjected to compressive stress. Depending on the type of parent rock gives the different crushing values of aggregate as a compressive strength varying from a minimum of about 45 MPa to a maximum of 545 MPa.
It is a fact that parent rock compressive strength does not exactly indicate the strength of aggregate in concrete.
For this reason assessment of the strength of the aggregate is made by using a sample of bulk aggregate in a standardized manner.
This testing method is known as an aggregate crushing value test.
The crushing value test of aggregate provides the resistance of an aggregate sample to crushing under a gradually applied compressive load.
Generally, the test is conducted on aggregate passing 12.5 mm and retained on a 10 mm sieve. The aggregate sample is filled in a cylindrical mold and a load of 40 tons is applied through a plunger in a compression testing machine.
The crushed aggregate sample which is finer than 2.36 mm is separated and expressed as a percentage of the original weight taken in the mold. The percentage of weight passed through the 2.36m IS sieve is known as the Aggregate crushing value.
In situations, when the aggregate value is 30 or higher the result may be a mistake and in such cases, the “ten percent fines value” should be determined and used instead.
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Aggregate Crushing Value Test (ACV Test)
AIM: Determination of Aggregate Crushing Value Crushing Strength of Coarse Aggregate.
Aggregate Crushing value test IS Code is 2386-4 (1963): Methods of Test for Aggregates for Concrete
Aggregate Crushing Value Apparatus
- A 15 cm dia. Steel cylinder with plunger and base plate.
- A straight metal tamping rod 16mm in diameter and 45 to 60cm long rounded at one end.
- A Weigh balance of accuracy up to 1 gam.
- IS sieves of sizes 12.5mm, 10mm, and 2.36mm
- A compression testing machine.
- The cylindrical measure has a diameter of 11.5 cm and 18cm in height.
- A compression testing machine has a loading capacity of 40 tons and can be operated to give a uniform rate of loading so that the maximum load is reached in 10 minutes.
Sampling for Crushing Test of Aggregate
For the Aggregate crushing value test, an aggregate sample passing through a 12.5 mm IS sieve and retained on a 10mm IS sieve is selected and dried to a temperature of 105 ºC to 110 ºC then cooled to room temperature.
To fill the cylindrical measure mold about 6.5 kg of a sample of aggregate is sufficient.
Read More: How to Check Compressive Strength of Concrete
Aggregate Crushing Value Test Procedure
- Take the Empty weight of cylindrical measure as W1.
- Fill aggregate sample passing through 12.5 mm and retained on 10 mm IS sieve in measuring cylinder in 3 equal layers such that each layer is subjected to 25 strokes using the tamping rod. Take the weight of aggregate with the measuring cylinder as W2.
- Find out the weight of aggregate sample W = W2 – W1
- Now, fill the aggregate sample in a 15 cm dia. and 13 cm height steel cylinder and level the surface of aggregate carefully and insert the plunger so that it rests horizontally on the surface.
- Place a steel cylinder with a plunger on the loading plate of the compression testing machine.
- Operate a Compression machine such that 40 tonnes of the load is applied on aggregate in approximately 10 min.
- Release load and remove the steel cylinder from the machine.
- Take out the crushed aggregate sample and sieve on with a 2.36mm IS sieve, care being taken to avoid loss of fines.
- Take off the weight of fraction passing through 2.36 mm IS sieve as (W3).
Calculation of Crushing Value Test of Aggregate
The crushing strength of aggregate can be found by the following formula,
“Aggregate crushing value is determined by taking a percentage of weight crushed aggregate sample passing through 2.36 mm IS Sieve divided by weight of aggregate sample taken for test”
The aggregate crushing value formula is given below,
Aggregate crushing value = (W3 / W) or W3 / (W2 – W1)
W1 = Empty weight of cylindrical Measure.
W2 = Weight of Aggregate with Cylindrical Measure
W = W2 –W1 = Weight of Aggregate Sample
W3 = Weight of crushed aggregate sample passed through 2.36 mm IS Sieve.
Read More: Aggregate Testing | 7 Test On Aggregates | Coarse Aggregate Test
Aggregate Crushing Value Test Result
For accurate test results conduct the test at least 3 times and take an average of 3 values.
Aggregate Crushing Value Test Lab Report
Aggregate Crushing Value Limits for Road Pavement
The below table shows the aggregate crushing value limits for different types of roads
Types of Roads / Pavements | Aggregate Crushing Value Limit |
Flexible Pavements | |
Soling | 50 |
Water bound macadam | 40 |
Bituminous macadam | 40 |
Bituminous surface dressing or thin premix carpet | 30 |
Dense mix carpet | 30 |
Rigid Pavements | |
Other than wearing course | 45 |
Surface or Wearing Course | 30 |
FAQs:
What is the aggregate crushing value test?
The crushing value test of aggregate provides the resistance of an aggregate sample to crushing under a gradually applied compressive load. Generally, the test is conducted on aggregate passing 12.5 mm and retained on a 10 mm sieve
Why aggregate crushing value test is done?
The strength of coarse aggregates is determined by the aggregates crushing test. The aggregate crushing value test provides resistance of an aggregate to crushing under a gradually applied compressive load. To construct a high-quality pavement, aggregate possessing low aggregate crushing value should be preferred.
Is code for crushing the value of aggregate?
The crushing value of the aggregate test is conducted as per IS IS:2386-Part 4-1963.
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