Detailed Impact Test on Road Aggregates with calculation of Impact value has been shown, also range of aggregate impact value is explained.
Toughness is the property of a material to easiest impact. Due to moving loads the aggregates are subjected to pounding action or impact and there is possibility of stones breaking into smaller pieces. Therefore a test designed to evaluate the toughness of stones i.e., the resistance of the stones to fracture under repeated impacts may be called Impact test on aggregates. The test can also be carried on cylindrical stone specimen known as Page Impact test. The aggregate Impact test has been standardized by Indian Standard Institution. The aggregate impact test is conducted as per IS-2386 Part IV. The aggregate Impact value indicates a relative measure of the resistance of aggregate to a sudden shock or an Impact, which in some aggregates differs from its resistance to a slope compressive load in crushing test. A modified Impact test is also often carried out in the case of soft aggregates to find the wet Impact value after soaking the test sample.
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Aggregate Impact Value Range:
1) Less than 10%---- Exceptionally Strong
2) 10-20%---Strong
3) 20-30%---Satisfactory for road surfacing
4) More than 35%-----Weak for road surfacing
APPARATUS:
1) Impact testing machine.
2) Cylindrical measure.
3) Tamping Rod.
4) IS Sieve.
5) Weighing Scale.
6) Oven.
PROCEDURE:
1) The sample consists of aggregates passing 12.5mm sieve and retained on 10mm seive and dried in an oven 4 hrs at a temperature 1000c to 1100C and cooled.
2) The aggregates are filled in the cylindrical measure in 3 layers and tamped 25 times with rounded end of the tamping rod and the surplus aggregates are struck off using the tamping rod as straight edge
3) The whole of the test sample from the cylinder measure is transferred to the cup and compacted by tamping with 25 strokes and the net weight is determined.
4) The test sample is subjected to a total of 15 blows, each being delivered at an interval of not less than 1 sec and hammer is made to fall at a height of 38 cms.
5) The crushed aggregate is removed and it is sieved on 2.36mm sieve and fraction passing the sieve is weighed.
I thank my students Mohammed Sameer, Manjunath Pujari, Guruprasad Gondi and Siddhaya Bhavimani for their assistance.
Big thanks to my Institution KLS Shri Vasantrao Potdar Polytechnic for permitting to carry out this experiment
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