Wednesday, September 4, 2013

Aggregate Impact Value Test

Hi,
AIM: to find the aggregate Impact value.

Theory:
Aggregate to be used as road materials must possess some properties or characteristics. Toughness is one of the highly required property which is necessary for the aggregates to bear the impact loads. 

Road aggregates are applied with the impact loads a millions of times in their life as the road materials. So they must be tested for their toughness before they are used in the pavement layers. 
Toughness can be tested using a Impact testing machine, which is an arrangement to apply the impact loads on the aggregates just like they are applied on the roads. 
Materials which get fractured or crushed into smaller particles are not tough. In this test we will find out the percentage of the weight of the aggregate sample which gets crushed with respect to the total weight of the sample. This percentage is known as the aggregate impact value and more the aggregate impact value less is the toughness of the road aggregates and vice verse.  

If impact value is less than 10% then aggregate is said to be exceptionally strong, if it is in range of 10 to 20% then they are good, aggregates having impact value less than 35% are considered satisfactory by the IRC(Indian Roads Congress).

Apparatus Used:  Aggregate Impact Load Testing Machine, IS Sieves of size 12.5 mm; 10 mm and 2.36 mm. Electronic weighing balance, tray.

Calculations:
Suppose weight of the Total aggregate samples in the cylindrical mould( which passed through 12.5 mm Sieve and retained on 10 mm Sieve) = W1
Let weight of the crushed aggregates(Which pass through 2.36 mm IS Sieve) = W2
Impact value of the aggregates(%) = W2/W1 *100

Results: Aggregate Impact Value =       %




Solved Example of Pinned Truss - the average normal and shear stresses in members and pins respectively and Pin Diamater

Hi, A simple truss has pin-connected members. The members carry only axial forces, but the pins have to bear the shear stresses. Given exa...