LAB TEST FOR DETERMINATION OF THE IMPACT VALUE OF COARSE AGGREGATE

OBJECTIVE: To determine the impact value of coarse aggregate.

APPARATUS: impact test machine with free falling hammer of 13.5 to 14kg with of fall of 380+-5mm,with supporting means of hammer whilst fastening or removing the cups; cylindrical steel cup of internal dia 102mm and 50mm deep; IS sieves 12.5mm,10mm and 2.36mm; cylindrical metal measure of internal dia 75mm and 50mm deep, tamping rod of 10mm dia,230mm long with rounded at one end, balance of 0.1gm accuracy, thermostatically controlled oven.

PROCEDURE:

1.      Take a representative air dried sample by quartering method or by a sample driver.

2.      Sieve it through 12.5 and 10mm sieves, take the material retained on 10mm but passed through 12.5mm.

3.      Keep it in oven for 4 hours at 100-110 cylinders.

4.      Take it out of oven and cool to the room temp.

5.      Take the cylindrical measure, fill up its 1/3 rd , and temp with 25 strokes with temp rod.

6.      Similarly, fill the total measure over flowing in next two layers by tempering each layer by 25 strokes

7.      Struck off, the surplus aggregate by using tamping rod as straight edge.

8.      Record the net weight of aggregate in the measure to the nearest 1gm.

9.      Place the compact testing machine on a firm floor or block without any packing or wedging on a leveled surface.

10.  Fix the cup firmly on the base of the machine.

11.  Fill the cylindrical steel cup with the aggregate taken in the metal measure in a single layer to upper face aggregate and allow it to fall freely over the aggregate.

12.  Subject the test sample to 15 such blows.

13.  Remove the crushed aggregate from the cup and sieve it through 2.36mm is sieve.

14.  Weight the fraction retained on 2.36mm sieve.

15.  If the difference between total weight taken before crushing and total weight retained + passing the 2.36mm sieve is more than 1 gm, then the test may be discarded and fresh test may be made.

16.  Two such tests shall be made.

17.  The average of two tests is reported as average aggregate impact value.

18.  Aggregate impact value(%)=(100*the fraction passing 2.36mm sieve)/(the weight of aggregate taken in the measure before crushing.