Aggregates are basic mineral materials that are used in construction. These include sand, gravel and crushed stone. Aggregates are used as raw materials in the construction of parking lots, sidewalks, bridges, streets and many more. They can be natural or manufactured. On average, the construction of houses requires 400 tonnes of aggregates, and the construction of a hospital requires 15,000 tonnes of aggregates. 

Why is aggregate testing required?

Aggregate testing is done to check the quality and properties of the aggregates. The different properties include strength, toughness, hardness, shape and water absorption. A coarse aggregate should own the following properties.

• Its shape must be cubical or angular.
• It should be free from any kind of organic matter, chemical or clay coating.
• It should be hard.
• Aggregate must be hard and durable.

What are the types of aggregate tests

There are 7 types of aggregate tests, which are mentioned below

1. Impact test
2. Crushing test
3. Abrasion test
4. Soundness test
5. Specific gravity and water absorption test
6. Shape test
7. Bitumen adhesion test

Impact test on aggregates

It is conducted to test the ability of aggregates to resist sudden impacts and shocks. It is carried out using Aggregate impact apparatus, IS sieves of 12.5 mm, 10.0 mm and 2.36 mm, weighing balance, tamping rod and cylindrical measure and cylindrical cup.

The aggregate impact value can be calculated using the formula (W1/W2) x 100, where W1 is the weight of the total sample, and W2 is the weight of aggregates passing the sieve. The impact value of aggregate used for surface wearing course should not exceed 30 per cent, and that for surface other than wearing course should not exceed 45 per cent.  

Crushing test on aggregates

The crushing test measures the strength of the aggregates. Aggregate crushing value is the relative resistance of aggregates under gradually applied compressive strength. The strength of the aggregate is inversely proportional to the crushing value. A lower crushing value indicates that the crushed fraction under the load is lower. The apparatus for aggregates crushing test includes a compressive testing machine, crushing mould, weighing machine and sieve of sizes 12.5 mm, 10 mm and 2.36 mm.

It can be calculated using the formula (W1/W2) x 100, where W1 is the weight of the total sample and W2 is the weight of the passing material. Its value shouldn’t exceed 30% of the concrete used for roads and pavements and 45% in the case of other structures.

Abrasion test on aggregates

The abrasion test measures the hardness of the aggregates and measures its ability to resist wear and tear. The apparatus required involves the Los Angles Abrasion machine, steel balls, weighing machine and sieves of 20 mm, 12.5 mm, 10 mm and 1.7 mm. The abrasion value of aggregates shouldn’t be more than 30 per cent for aggregates used for surface wearing course and not more than 45 per cent for other surfaces.

Soundness test on aggregates

Soundness test is conducted to measure the durability of aggregates to face adverse weather conditions. To gauge their reaction to those changes, the aggregates are subjected to different situations like rainwater, groundwater, and other atmospheric conditions. This test is carried out using sodium sulphate or magnesium sulphate solution, weighing balance, oven and IS sieves.

The loss in weight after 10 cycles should not be more than 12% for Sodium Sulphate and 18% for Magnesium Sulphate.

Specific gravity and water absorption tests on aggregates

Specific gravity is the ratio of the weight of a given volume of aggregate to the weight of an equal volume of water.

The water absorption of aggregate is the percentage of water absorbed by a dry aggregate when it is kept in 27 degrees centigrade of water for 24 hours.

The apparatus required for this test is a density basket, weighing balance, water tank, tray and IS sieve of 10 mm and 20 mm. The specific gravity of coarse aggregates ranges from 2.5 to 3, and water absorption ranges from 0.1% to 2.0%.

Shape test on aggregates

The shape of the aggregate is determined by the flakiness index test and elongation index test. The flakiness index is the percentage by weight of aggregate particles whose dimension is less than 0.6 times their mean size. The elongation index of aggregate is the percentage by weight of aggregates whose length is 1.8 times greater than their mean dimension.

Shape test can be conducted using thickness gauge, length gauge, weighing balance and IS sieve. The recommended value lies between 15% to 35% depending upon the area of usage. 

Bitumen adhesion test

Bitumen can get bonded with different aggregates when they are dry and dust-free. Adhesion problems might occur when the aggregate is wet and cold. This problem can be solved by removing the moisture from the aggregate and increasing the temperature. The bitumen adhesion test is conducted to determine the adhesion of the bituminous binder to aggregate in the presence of water.

The apparatus required involves a water bath, oven, sieve and mixer to mix aggregate and bitumen. The recommended stripping value of the bitumen adhesion test should not exceed 5 per cent.

These were all the different tests that are conducted to determine the properties of aggregates. Different types of aggregates have varied usage, and thus is necessary to determine their quality. Aggregates are important for the strength and longevity of any structure, and thus these tests

are not to be ignored. Most of the tests are conducted in the laboratory, but some can be conducted on-site to determine the quality of aggregates. 

Explore our diverse range of aggregates in our product listings that perfectly align with the testing methods discussed in our blog. From fine sand to graded stones, our selection is curated to meet the highest industry standards.