Objective

For determination of the aggregate crushing value of coarse aggregate, which passes 12.5 mm. IS sieve and retained on 10 mm. IS sieve. 

Reference Standard

IS: 2386 (Part IV)-1963 Methods of test for aggregate for concrete Part IV Mechanical Properties.

Equipment & Apparatus

• Steel Cylinder
• Sieves (12.5mm,10mm)
• Cylindrical metal measure
• Tamping Rod
• Balance (0-10kg)
• Oven (300⁰c)
• Compression testing Machine (2000KN) 

  

Preparation of sample

Test sample consist of aggregate passing a 12.5mm IS sieve and retained on a 10mm IS sieve. The aggregate to be tested is dried in oven for a period of not less than 4 hours.

 Procedure

1. The cylindrical steel cup is filled with 3 equal layers of aggregate and each layer is tamped 25 strokes by the rounded end of tamping rod and the surplus aggregate struck off, using the tamping rod as a straight edge.
2. The net weight of aggregate in the cylindrical steel cup is determined to the nearest gram (W_A) and this weight of aggregate is used for the duplicate test on the same material.
3. The cup is fixed firmly in position on the base of the machine and the whole of the test sample is added in thirds, each third being subjected to 25stokes from tamping rod.
4. The surface is leveled and the plunger is inserted so that it rests horizontally on the surface. The whole assembly is then placed between the platens of testing machine and loaded at a uniform rate so as to reach a load of 40 tones in 10 minutes.
5. The load is then released and all aggregate is removed from the cup and sieved on 2.36 mm. IS sieve until no further significant amount passes in one minute.
6. The fraction passing the sieve is weighed to an accuracy of 0.1 g (W_B)

Calculation

The ratio of the weight of fines formed to the total sample weight in each test is to be expressed as a percentage, to the first decimal place.

Aggregate crushing Value =(W_B/W_A) × 100 

Record

The mean of the two results is reported to the nearest whole number as the aggregate crushing value of the tested material.           

Safety & Precautions:

• Use hand gloves while removing containers from oven after switching off the oven.
• To wear safety shoes & helmet during the time of test.
• Before testing, machine should be checked.
• After test electric supply should be off.
• After test clean the sieve by brush.
• Keep all the exposed metal parts greased.
• Keep the guide rods firmly fixed to the base & top plate.
• Equipment should be cleaned thoroughly before testing & after testing.