Aggregates are defined as the coarse materials provided in any substance to gain a certain strength such as roads , pavements structures etc. the aggregates are basically preferred and considered because of the interlocking abilities of the sample which helps to gain strength.
The particles are usually irregular in shape pointed, round oval etc. these when come together makes the sample interlocked by its fitting in properties therefore, they are considered the most compatible in the case of roads or paved structures.
Attrition is defined as the surface rubbing under some heavy loads tend to make the interlocking abilities considerably weaker. This test is used to determine the measure of the rate of the granular particles wear also termed as the resistance to abrasion value.
This is a fast test as compared to abrasion. This takes place because of the hitting of one surface with another. This subjects the sample towards smaller materials. The test is performed for the weathering, degradation, and an indication for abrasion values.
It comprises of cylinders with dia 20cm and a depth of 34cm set at an angle corresponding to 30’ along rotational axis.
The sample is adopted under specified limits such as specific gravity:
The following table is used for the grading based on the sieves size:
Figure 1 Deval Attrition Testing Machine
- Deval machine
- Sieves with IS: 1.7mm, 4.75mm, 10mm.12.5mm, 20mm, 25mm, 40 mm
- Weighing balance (5 to 10 kg measuring capacity)
- Oven for dehydrating
- Sample adopted is to be compatible with conditions stated in the above table.
- Aggregates must be well cleaned and dried in the oven with temperature range of 110.
- A grouping is considered in accordance with standards.
- Sample is placed in the machine, then enclosed with the lid.
- Machine is than subjected to revolutions at 30-33 rev/min with a total of 10000 cycles with a consistent speed balanced all around.
- Machinery is paused after the set of cycles completed with the sample removed onto some plate.
- These are then subjected under standard strainers with the dust passing through sieve of 1.7mm.
- The weight is dependent on the specific gravity as stated in standard.
Sample weight (original), W1 = _______ g
Sample weight (retained), W2 = _______ g
Weight of sample passing the IS Sieve of 1.7mm = W1– W2 = _______ g
Attrition value (Deval) = (W1– W2)*100
The sample is observed by the above standard values and its grade is decided based on the tables as listed above.
- The sample is to be properly cleaned.
- The machine is cleaned properly.
- The sample is subjected towards proper set of revolutions.
- Proper sieving is performed.