The determination of aggregate crushing strength is an important test in your civil engineering lab.You know that aggregates are the one the basic unit of building materials.Aggregates are used in several construction processes such as in concrete, road construction etc..
When talking in transportation engineering perspective, as you know that coarse aggregates are used in the subgrade and surface course of the pavement construction.
The aggregates used in the subgrade should have the property of resisting the wheel load acting on the pavement and should provide a stable subgrade to the pavement.The aggregates used in the surface course have the property of resistance to surface abrasion under traffic.
In road construction, the quality of aggregates is assessed by the crushing strength of aggregates.For higher quality of roads, the aggregate should possess low aggregate crushing value.
Here I am going to teach you how to determine the crushing strength of aggregates.First, let us check what are the various apparatus needed for this experiment.
Apparatus needed for finding the crushing strength of aggregate
- Steel cylinder consisting of open ends at both sides having an internal diameter of 152mm.
- Cylindrical measure to measure the quantity of aggregates needed for the test.
- Tampering rod
- A balance of capacity 3kg.
- A compressive testing machine having capable of applying 40 tonnes.The rate of loading is 4 tonnes per minute.
Procedure for crushing strength of aggregate
- Before testing, the aggregate should be in surface dry condition.You can achieve the dry condition of aggregate by placing aggregates in an oven for 4 hours at 100-degree Celcius.
- The aggregates passing through 12.5mm and retained on 10mm IS sieves are selected for finding aggregate crushing strength.
- After sieving aggregates, a cylindrical measure is taken and find the empty weight of cylindrical measure(We).It is then filled with aggregates in three layers with 25 blows to each layer using a tamping rod.
- After filling the cylindrical measure, level the top of the cylindrical measure by using a tamping rod.Measure the weight of cylindrical measure with aggregates (Wa).
- After this, you need to fill your steel cylinder with aggregates taken from the cylindrical measure.Do not miss any aggregates while you transferring the aggregates from cylindrical measure to steel cylinder.
- The steel cylinder should be filled with 3 layers and 25 blows to each layer using the tamping rod.After the filling of the steel cylinder, you need to place the plunger over steel cylinder.In the above picture, you can see the steel cylinder, plunger and cylindrical measure.
- After this, place the steel cylinder with the plunger inside the compression testing machine.
- The load is applied to the plunger at a uniform rate of 4 tonnes per minute.Wait for 10 minutes and the total load applied to the aggregates will be 40 tonnes.
- After applying the load, the crushed aggregates are taken and then passed through 2.36mm sieve.Take the weight of crushed aggregates passing through 2.36 mm sieve.Let the weight of aggregates passing through 2.36mm sieve be W2.
Calculation of aggregate crushing value
The aggregate crushing value is defined as the ratio of the weight of fines passing through specified IS (here 2.36mm sieve) to the total weight of sample expressed in percentage.
W1= Weigh of the total aggregates (Wa-We)
W2= Weigh of aggregates passing through 2.36mm IS sieve.
Aggregate crushing value=( W2 / W1 ) × 100
Hope you could understand this aggregate crushing strength experiment.Your happiness is my happiness.if you like this post? Don’t forget to share it with your friends.