The aggregate crushing value test is performed on coarse aggregates to determine their resistance to crushing under a gradually applied compressive load. This test measures the percentage by weight of the crushed material obtained when test aggregates are subjected to a specified load under standardized conditions. The aggregate crushing value is a numerical index of the strength of the aggregate, and it is crucial in the construction of roads and pavements.
A lower crushing value is recommended for roads and pavements as it indicates a lower crushed fraction under load, resulting in a longer service life and more economical performance. Therefore, the aggregates used in roads and pavement construction must be strong enough to withstand crushing under roller and traffic.
In cases where the aggregate crushing value is 30 or higher, the result may be anomalous, and in such cases, it is recommended to determine the ten percent fines value instead. It is essential to ensure that the aggregates used in construction meet the required specifications to ensure the durability and longevity of the infrastructure. Therefore, the aggregate crushing value test is an important tool for determining the strength and suitability of the aggregates for road and pavement construction.
Aggregate Crushing Value Test
The purpose of this test is to evaluate the suitability of coarse aggregate for use in various types of road construction. Specifically, the test aims to determine the aggregate crushing value of the coarse aggregate. This value is an indicator of the strength and durability of the aggregate, which is important for ensuring that the road is able to withstand the stresses and strains of regular use. By assessing the crushing value of the coarse aggregate, engineers and construction professionals can make informed decisions about which materials to use in road construction projects.
Apparatus
The equipment list includes several items that are commonly used in materials testing and construction applications. These items include a steel cylinder that is 15 cm in diameter, along with a plunger and base plate. The cylinder is likely used to compact materials, such as soil or concrete, to a specific density or consistency.
Additionally, a straight metal tamping rod is included in the equipment list. This rod is 16mm in diameter and 45 to 60cm long, and is rounded at one end. This tool is often used in construction and materials testing to compact soil, concrete, or other materials into a specific shape or consistency.
A balance with a capacity of 3 kg and an accuracy of one gram is also included. This device is likely used to weigh materials or samples during testing, and is designed to provide precise and accurate measurements.
The equipment list also includes several IS sieves, which are commonly used in materials testing to separate and classify materials based on their size. Specifically, the sieves in this equipment list are sized at 12.5mm, 10mm, and 2.36mm.
A compression testing machine is also included in the equipment list. This device is used to test the strength and durability of materials by subjecting them to compressive forces. This machine is likely used in construction and materials testing applications to evaluate the performance of materials under various conditions.
Finally, the equipment list includes a cylindrical metal measure that is 11.5cm in diameter and 18cm in height. This measure is designed to retain its shape under rough usage and is used to hold materials or samples during testing. The measure is likely used in materials testing to accurately measure and evaluate the properties of various materials. Additionally, a dial gauge is included in the equipment list, which may be used in conjunction with the compression testing machine to measure the deformation or displacement of materials under load.
Sampling of Aggregates
To conduct a test on coarse aggregate, a sample that passes through a 12.5mm IS sieve and is retained on a 10mm IS sieve is selected. This sample is then heated to a temperature of 100 to 110°C for a period of 4 hours and allowed to cool to room temperature. The quantity of aggregate used in the test should be such that, after tamping, the depth of material in the cylinder is 10cm.
To determine the appropriate quantity of aggregate for the test, the cylinder is filled with the sample in three layers of approximately equal depth. Each layer is tamped 25 times with a tamping rod, and the surface is leveled off using the rod as a straight edge. Care must be taken not to break the particles, particularly in the case of weaker materials.
Once the sample is properly prepared, the weight of the material comprising the test sample is determined, and this weight is recorded as weight A. For the repeat test, an equal weight of sample is taken.
Procedure of Aggregate Crushing Value Test
To begin testing the material, the cylinder must first be placed onto the base plate and weighed (W). The sample must then be prepared in three layers and tamped with the rod for 25 strokes per layer. It’s important to be cautious with weak materials to avoid breaking the particles during this step. After tamping, the sample should be weighed (W1).
Next, the surface of the aggregate should be leveled carefully and the plunger should be inserted so that it rests horizontally on the surface. It’s crucial to ensure that the plunger does not jam in the cylinder. The cylinder with the plunger should then be placed onto the loading platform of the compression testing machine.
The load should be applied at a uniform rate to achieve a total load of 40T in 10 minutes. Once this is achieved, the load can be released and the material can be removed from the cylinder. It’s essential to sieve the material with a 2.36mm IS sieve while taking care to avoid losing fines.
Finally, the fraction of material that passes through the IS sieve should be weighed (W2). Following these steps carefully will ensure accurate testing results.
Calculation of Aggregate Crushing Value
In order to determine the aggregate crushing value, a test is conducted where the weight of fines formed is measured in relation to the weight of the total sample. The result is expressed as a percentage and recorded to the first decimal place.
To calculate the aggregate crushing value, the weight of the fraction passing through the appropriate sieve (W2) is divided by the weight of the surface dry sample (W1-W). This calculation is then multiplied by 100 to obtain the percentage value.
The test is conducted twice and the mean of the two results is taken, rounded to the nearest whole number, in order to obtain the aggregate crushing value. This value is important in determining the strength of the aggregate and its ability to withstand crushing under a specific load.
Result
The aggregate crushing value of the given sample=
Aggregate Crushing Values for Roads and Pavement Construction
The table below shows limits of aggregate crushing value for different types of road construction:
| Types of Roads / Pavements | Aggregate Crushing Value Limit |
| Flexible Pavements | |
| Soling | 50 |
| Water bound macadam | 40 |
| Bituminous macadam | 40 |
| Bituminous surface dressing or thin premix carpet | 30 |
| Dense mix carpet | 30 |
| Rigid Pavements | |
| Other than wearing course | 45 |
| Surface or Wearing course | 30 |