DETERMINATION OF IMPACT VALUE OF COARSE AGGREGATE
Test Standard : 2386-Part IV: 1963
- Impact test apparatus with free-falling hammer of 13.5 to 14kg with a height of fall of 380±5mm, with supporting means of hammer whilst fastening or removing the cups.
- Cylindrical steel cup of internal diameter 102mm and 50mm deep; IS sieves 12.5mm, 10mm and 2.36mm, a cylindrical metal measure of internal diameter 75mm and 50mm deep.
- Tamping rod of 10mm diameter, 230mm long with rounded at one end,
- Balance of 0.1g accuracy.
- Hot air electric oven.
- Take sample of aggregate by quartering method. Test sample shall be prepared by passing the aggregate from 12.5mm IS Sieve and retained on 10mm IS Sieve. Test sample shall be dried in oven for a period of 4 hours at a temperature of 100 to 1100C & cooled. Test sample shall be filled in a cylindrical metal measure in three layers with 25 number of tamping in each layer. The third layer/top layer shall be overfilled & surplus aggregates shall be struck off using tamping rod. The net weight of the test sample in the measure shall be determined to nearest 1.0 gms (say W1, gms)
- Fix the impact test apparatus on firm & levelled ground without any packing, wedging on the plate so that it is rigid & hammer guide columns are vertical.
- The cup shall be fixed firmly in position on the base of the apparatus & whole of the test sample shall be placed in it &compacted by a single tamping of 25 number of strokes by tamping rod. Lift the hammer until its lower face is 380mm above the upper face of the aggregate in a cup & subjected to a total of 15 number of blows each being delivered at an interval of not less than one second.
- The crushed aggregate shall be removed from the cup & sieved over 2.36mm IS Sieve until not further significant amount passes in one minute. The fraction passing the sieve shall be weighed to an accuracy of 0.1gms (say W2, gms) & retained on the sieve shall also be weighed (say W3, gms), if the total weight W2+W3 is less than the initial weight W1 by more than 1.0 gms, result shall be discarded & fresh test shall be made. Impact value shall be reported in percentage to the nearest first decimal place.
Impact value (%) = (W2/W1) x100
|Aggregate impact value test format|
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