Short Answer:

The crushing value of aggregates is a measure of their strength under gradual compressive load. It shows how much the aggregate can resist being crushed when pressure is applied slowly. A lower crushing value means the aggregate is strong and suitable for use in heavy-duty structures like roads and pavements.

This property is important because it helps engineers choose the right type of aggregate for construction work. Stronger aggregates make concrete or road layers more durable and reduce the chances of cracks or failure under load. That is why testing the crushing value is essential before using aggregates in any structure.

Detailed Explanation:

Crushing value of aggregates

The crushing value of aggregates is a crucial property used to assess their ability to resist crushing when a compressive load is applied. In civil engineering, especially in road construction and heavy concrete works, materials need to withstand loads from vehicles, structures, or environmental pressure. Aggregates that break easily under load may lead to premature failure, so their crushing strength must be checked before use.

The crushing value is expressed as a percentage of the weight of crushed material to the original sample weight. A lower percentage means the material is stronger and more suitable for construction. For high-quality construction work, especially for roads, the aggregate crushing value should generally be below 30%.

Why is it important?

Crushing value is important because it helps in selecting the right aggregates for different structural works. If weak aggregates are used, they may crush under load, leading to cracks, uneven surfaces, and early damage. This not only increases maintenance costs but also risks safety and performance.

The crushing value gives an idea about the strength and quality of aggregates. Engineers use this test to ensure that aggregates used in foundations, roads, or concrete have enough resistance to compressive stress. For example, in road construction, the top layer of the road is exposed to heavy vehicle loads. If weak aggregates are used, the surface will wear out quickly, resulting in potholes and damage.

How is it tested?

The crushing value test is performed in a laboratory using a compression testing machine. The standard procedure is:

1. Sample Preparation: A dry sample of aggregate is taken, passing through a 12.5 mm sieve and retained on a 10 mm sieve. About 3 kg of this sample is required.
2. Filling the Mould: The aggregate is placed in a cylindrical steel mould in three equal layers, each layer compacted with 25 strokes of a tamping rod.
3. Applying the Load: The filled mould is placed under a compression machine, and a load of 40 tons is applied gradually over 10 minutes.
4. Sieve Analysis: After the test, the crushed aggregate is sieved through a 2.36 mm sieve. The weight of the fine material passing through the sieve is measured.
5. Calculation:
   Crushing Value (%) = (Weight of fines / Original weight) × 100

A lower crushing value means higher strength and suitability for heavy loads. Values between 20–30% are considered good for most construction works.

Conclusion:

The crushing value of aggregates indicates how much they can resist being crushed under load. It is a key factor in determining their strength and suitability for construction. By testing this property, engineers ensure that the selected materials will perform well under pressure and provide long-lasting strength to structures like roads, buildings, and foundations.