IMPACT VALUE TEST FOR AGGREGATE (IS 2386 PART IV :1963)

 IMPACT VALUE OF AGGREGATE

OBJECTIVE

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

REFERENCE STANDARDS

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

EQUIPMENT & APPARATUS

§  Aggregate Impact Test Machine

§  Sieves (12.5mm,10mm)

§  Cylindrical metal measure

§  Tamping Rod

§  Balance (0-10kg)

§  Oven(300⁰c)

  

             Fig:-Showing Aggregate Impact Value Test Apparatus

PREPARATION OF TEST SAMPLE

Test sample consist of aggregate passing a 12.5 mm IS sieve and retained on a 10 mm 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 placed in it and compacted by a single tamping of 25 strokes of tamping rod.

4.      The hammer is raised until its lower face is 380 mm. above the upper surface of the aggregate in the cup, and allowed to fall freely onto the aggregate 15 times, each being delivered at an interval of not less than one second.

5.      The crushed 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)

Table:-Observation table for impact testing

wt taken (in gm)	332	330.5	328
retd  2.36 mm (in gm)	275	282.5	269
Pass 2.36 mm (in gm)	57	48	59
% impact value	17.16	14.52	17.98

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 impact Value =  (W_B / W_A) × 100

Avg. Impact Value :-   16.55 %

PRECAUTIONS

§  Use hand gloves while removing containers from oven after switching off the oven.

§  To wear safety shoes & goggles at the time of testing.

§  Before testing, machine should be properly checked.

§  Special care should be taken that no outer air enters when using the balance.

§  After test clean the sieve by a smooth brush.

§  Keep all the exposed metal parts greased.

§  Keep the guide rods firmly fixed to the base & top plate.

§  Equipment should be clean thoroughly before testing & after testing.