Sunday, August 23, 2020

IMPACT VALUE OF AGGREGATE

Determine the impact value of aggregate, The impact value test of aggregate pdf are discussed.

IMPACT VALUE OF AGGREGATE 


Impact value of  Aggregates are determined according to the standards, The impact value test of aggregate pdf  as follows.
The property of a material to withstand impact is known as toughness. Due to movement of vehicles on the road the aggregates are subjected to impact as a result of it, the aggregate are breaking down into smaller pieces. The aggregates should have sufficient toughness to withstand their disintegration due to impact. This characteristic of withstand to impact is measured by impact value test. The aggregate impact value is a measurement of withstand to sudden impact or shock, which may differ from its resistance to gradually applied compressive load/ wheel load.



Aggregate Impact image


APPARATUS: 

  • Impact testing machine, 
  • Cylinder, 
  • Tamping rod, 
  • IS Sieve 125.mm, 10 mm and 2.36 mm, 
  • Weight balance.

PROCEDURE:

1. The aggregate sample should passing 12.5 mm IS sieve and retained on 10 mm IS sieve and dried in an oven for 4 hours at a temperature of 100 ̊ C to 110 ̊ C.

2. The aggregates are filled about 1/3 full in the cylindrical container and tamped 25 times by rounded end tamping rod.

3. The rest of the cylindrical container should be filled by two layers and each layer being tamped 25 times by tamping rod. 

4. The overflow of aggregates in the container is cut off by tamping rod using it has a straight edge. 

5. Then weigh the entire aggregate sample in a measuring cylinder.

6. The aggregates from the cylindrical measure are carefully filled into the cup which is firmly fixed in position on the base plate of Impact testing machine. Then it is tamped 25 times. 

7. The hammer is raised until its lower face is 38 cm above the upper surface of aggregate in the cup as derived in Indian standards and allowed to fall freely on the aggregates. The total of 15 such blows each being delivered at an interval of not less than one second. The crushed aggregate is than removed from the cup and the whole of it is sieved on 2.366 mm IS sieve until no significant amount passes. The amount of aggregate passing the sieve is weighed accurate to 0.1 gm. Repeat the above steps with other fresh sample. 

8. Not the previously given aggregate sample weight of the oven dry sample be W1 gm and the weight of tested aggregate passing 2.36 mm IS sieve be W2 gm. Then aggregate impact value is calculated as the % of fines of the total weight of the sample. 

OBSERVATION & CALCULATION :- 

imapct value table image

Aggregate Impact Value

PRECAUTIONS:

1. As the hammer is heavy, be cautions to keep away from falling mass, to avoid accidents; as a measure of safety the hammer should be locked in position before carrying out any operation at the base of the impact testing machine.

2. The sample should be subjected to 15 blows of the hammer at not less than 1 second interval.



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