In the realm of construction and infrastructure development, the quality of stones and aggregates used plays a pivotal role. Two fundamental mechanical properties are of utmost importance: resistance to crushing during construction and the ability to withstand surface abrasion under traffic conditions. The Aggregate Crushing Value (ACV) test serves as a crucial indicator of the strength of aggregates used in construction, ensuring the stability and durability of pavement structures.

The Significance of Aggregate Strength

In the realm of construction, the strength of aggregates takes center stage. Aggregates must possess the resilience to withstand the formidable forces exerted by traffic wheel loads. The implications of weak aggregates are dire, potentially jeopardizing the stability and longevity of pavement structures. Hence, it is imperative to evaluate the strength of coarse aggregates, and this is precisely where the Aggregate Crushing Value test comes into play.

The Objective of the Test

At its core, the Aggregate Crushing Value test aims to assess an aggregate’s capacity to endure crushing under a gradual and increasing compressive load. This test holds immense importance in ensuring the quality of construction and pavements, as it helps in selecting aggregates with low ACV values, which are preferred for creating high-quality road surfaces.

The Essential Apparatus

To perform the Aggregate Crushing Value test effectively, a set of crucial apparatus is employed:

  • Steel Cylinder with Open Ends: This cylindrical container, with an internal diameter of 152mm and a square base plate, serves as the housing for the test sample during the examination.
  • Plunger: Equipped with a piston featuring a 150mm diameter and a hole along the stem, the plunger allows for smooth lifting and placement within the cylinder.
  • Cylindrical Measure: This cylindrical vessel boasts an internal diameter of 115mm and a height of 180mm, facilitating precise measurement of the aggregates.
  • Steel Tamping Rod: With one rounded end and a diameter of 16mm, this rod, typically 450 to 600mm in length, aids in compacting the aggregate layers.
  • Balance: To ensure accuracy, a balance with a 3 kg capacity and a 1g accuracy is used for weighing the test samples.
  • Compressive Testing Machine: This robust machine can apply a load of 40 tonnes at a uniform rate of 4 tonnes per minute.

Conducting the Test

The procedure for the Aggregate Crushing Value test unfolds through the following steps:

  1. Sample Selection: A representative sample of aggregate passing the 12.5mm IS sieve and retained on the IS sieve is chosen for the standard test. The aggregate must be in a surface-dry condition.
  2. Sample Preparation: The selected aggregate sample undergoes drying by heating it to a temperature between 100°C and 110°C for a duration of 4 hours. Once cooled to room temperature, it is ready for testing.
  3. Sample Tamping: The cylindrical measure is filled with the test sample in three equal layers, with each layer being tamped 25 times using the rounded end of the tamping rod. The aggregate is then leveled at the top of the measure.
  4. Load Application: The cylinder, with the test sample, is placed on the base plate of the testing machine. A compressive load is applied through the plunger at a uniform rate of 4 tonnes per minute until the total load reaches 40 tonnes.
  5. Sieve Analysis: After the test, the crushed aggregates are extracted from the cylinder and sieved using a 2.36mm IS sieve. The material that successfully passes through the sieve is carefully collected.

Calculating the Aggregate Crushing Value

The crux of the test lies in calculating the Aggregate Crushing Value (ACV), which is expressed as the ratio of the weight of fines that pass the specified 2.36mm IS sieve to the total weight of the sample, presented as a percentage:

ACV=(W2​/W1)×100

Here, W1 denotes the total weight of the dry sample, while W2 represents the weight of the portion of crushed material that effectively passes through the 2.36mm IS sieve.

Reporting the Results

To ensure accuracy, the mean of the crushing values obtained in two tests is reported as the aggregate crushing value. This practice provides a more comprehensive assessment of the aggregate’s strength.

Acceptable Limits

In the context of cement concrete pavement, the aggregate crushing value should not exceed 30%. However, for surfaces that are subjected to more wear and tear, a stricter limit of 45% is imposed. These limits are crucial in maintaining the quality and resilience of road surfaces.

(Read abrasion test of aggregate .)

FAQs:

What is the Aggregate Crushing Value (ACV) test?

The ACV test is a standardized procedure used to assess the ability of coarse aggregates to withstand crushing under a gradually applied compressive load. It is commonly used in the construction industry to evaluate the strength of aggregates for road construction and other applications.

Why is the ACV test important in construction?

The ACV test is essential because it helps ensure that aggregates used in construction projects, particularly for road surfaces, are strong enough to withstand the stresses imposed by traffic loads. Weak aggregates can compromise the durability and safety of the infrastructure.

What apparatus is used in the ACV test?

The ACV test requires specific apparatus, including a steel cylinder, plunger, cylindrical measure, steel tamping rod, balance, and a compressive testing machine. These tools are necessary to perform the test accurately.

How is the sample prepared for the ACV test?

The sample for the ACV test is selected to pass a 12.5mm IS sieve and retained on the IS sieve. It should be in a surface-dry condition. The sample is then dried by heating at a specific temperature and duration before testing.

What is the significance of tamping during the test?

Tamping is crucial because it ensures uniform compaction of the aggregate sample in the cylindrical measure. It helps in achieving consistent and reliable test results.

What is the acceptable limit for the ACV in cement concrete pavement?

The acceptable limit for the ACV in cement concrete pavement typically should not exceed 30%. This limit is set to maintain the quality and durability of road surfaces.