Description

Aggregate Impact Value testing

 

The aggregate impact value gives a relative measure of the resistance of the

aggregate to sudden shock or impact.

The particular purpose which an aggregate is meant to serve requires the aggregate to

have a particular strength which is usually stated in the specification. This test provides

a method for measuring this strength.

 

Method outline. A test specimen, of chosen fractions, is compacted in a standardized

manner, into an open steel cup. The specimen is then subjected to a number of

standard impacts from a dropping weight. The impacts break the aggregate to a degree

which is dependent on the aggregate’s impact resistance. This degree is assessed by a

sieving test on the impacted specimen and is taken as the aggregate impact value.

 

 

Sampling. The sample used for this test shall be taken in accordance with Chapter

 

Equipment

Impact testing machine. The machine shall be of the general form shown in Figure have a total mass of between 45 kg and 60 kg and shall have the following parts:

 

1. A circular metal base, with a mass of between 22 kg and 30 kg, with a plane lower

surface of not less than 300 mm diameter and shall be supported on a level and

plane concrete or stone block floor at least 450 mm thick. The machine shall be

prevented from rocking during operation of the machine

 

2. A cylindrical steel cup, having an internal diameter of 102 mm plus or minus 0.5

mm and an internal depth of 50 mm plus or minus 0.25 mm. The walls shall be not

less than 6 mm thick and the inner surfaces shall be case hardened. The cup shall

be rigidly fastened at the center of the base and be easily removed for emptying.

 

3. A metal hammer, with a mass of between 13.5 kg and 14.0 kg, the lower end of

which shall be cylindrical in shape, 100.0 mm plus or minus 0.5 mm diameter and

50 mm plus or minus 0.15 mm long, with a 1.5 mm chamfer at the lower edge, and

case hardened. The hammer shall slide freely between vertical guides so arranged

that the lower part of the hammer is above and concentric with the cup.

 

4. Means for raising the hammer, and allowing it to fall freely between the vertical

guides from a height of 380 mm plus or minus 5 mm on to the test sample in the

cup, and means for adjusting the height of fall within 5 mm.

 

5. Means for supporting the hammer whilst fastening or removing the cup.

 

6. Square-hole perforated plate test sieves, of sizes 14.0 mm and 10.0 mm and a woven-

wire 2.36mm test sieve.

 

7. A cylindrical metal measure, of sufficient rigidity to retain its form under rough usage

and with an internal diameter of 75 mm plus or minus 1 mm and an internal depth of 50

mm plus or minus 1 mm.

 

8. A tamping rod, made out of straight iron or steel bar of circular cross section, 16 mm

plus, or minus 1 mm diameter and 600 mm plus or minus 5 mm long, with both ends

hemispherical.

 

9. A balance, of capacity not less than 500 g and accurate to 0.1 g