Introduction to Aggregate Impact Value Test
The Aggregate Impact Value (AIV) test is a standardized method for assessing the resistance of aggregates to sudden impact or shock. This test is vital for evaluating the mechanical strength and durability of aggregates used in construction, particularly for road works, concrete structures, and railway ballast.
The test is performed according to IS:2386 (Part IV)-1963 "Methods of Test for Aggregates for Concrete - Mechanical Properties" and provides a quantitative measure of aggregate toughness under dynamic loading conditions.
Aggregate Impact Value (AIV): The percentage by weight of fines (passing through a 2.36mm sieve) produced from an aggregate sample after subjecting it to a standard impact load. Lower AIV indicates stronger aggregates with better resistance to impact.
Why Determine Aggregate Impact Value?
Understanding the impact resistance of aggregates is crucial for several reasons:
Road Construction
Aggregates in road surfaces must withstand repetitive impact forces from vehicles. Weak aggregates would quickly degrade under traffic loads.
Structural Integrity
In concrete structures, aggregates with high impact resistance contribute to overall durability and resistance to dynamic loads.
Construction Applications
Different construction applications require aggregates with specific strength properties. AIV helps select appropriate materials for each use case.
Long-term Performance
Aggregates with low impact values maintain their integrity over time, reducing maintenance requirements and extending infrastructure lifespan.
According to IS:383 and various international standards, the maximum allowable Aggregate Impact Value is typically:
• ≤ 30% for concrete used for wearing surfaces (pavements, floors)
• ≤ 45% for other concrete applications
• ≤ 25% for high-quality road surfacing
• ≤ 35% for base course in road construction
Required Equipment
To conduct the Aggregate Impact Value test, you'll need the following equipment:
Impact Testing Machine
A standardized apparatus consisting of a metal base with a cylindrical steel cup, a metal hammer weighing 13.5-14.0 kg, and a mechanism to drop the hammer from a height of 380mm.
Balance
A precision balance with accuracy of at least 0.1g for weighing aggregate samples and fractions.
IS Sieves
12.5mm, 10.0mm, and 2.36mm sieves for sample preparation and post-test analysis.
Oven
For drying samples at 100-110°C to constant weight.
Tamping Rod
A 16mm diameter, 60cm long rounded steel rod for tamping the aggregate in the cup.
Trays & Containers
For handling, drying, and storing aggregate samples.
Aggregate Impact Value Test Procedure
Follow these steps to conduct the Aggregate Impact Value test accurately:
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Sample Preparation
Select a representative sample of the aggregate to be tested. The sample should be dry and clean. Sieve the sample through 12.5mm and 10.0mm sieves. Use the aggregates that pass through the 12.5mm sieve but are retained on the 10.0mm sieve for testing.
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Oven Drying
Dry the selected aggregate fraction (10.0mm - 12.5mm) in an oven at a temperature of 100-110°C for 4 hours or until a constant weight is achieved. Cool the sample to room temperature before testing.
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Preparing the Test Specimen
Fill the cylindrical steel cup of the impact testing machine with the prepared aggregate sample in three equal layers. Each layer should be tamped 25 times with the tamping rod. The final level of the aggregate should be about 5mm below the top edge of the cup. Record the exact weight of the aggregate in the cup (W₁).
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Performing the Impact Test
Secure the cup with the aggregate sample in the impact testing machine. Raise the hammer to a height of 380mm above the upper surface of the aggregate and allow it to fall freely onto the aggregate. Apply a total of 15 such blows, each separated by an interval of not less than one second.
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Sieving After Impact
After completing the 15 blows, remove the aggregate from the cup and sieve it through a 2.36mm IS sieve. Weigh the portion that passes through the 2.36mm sieve (W₂) and the portion retained on the sieve (W₃). Ensure that W₁ = W₂ + W₃ to verify that no material has been lost during the test.
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Calculation
Calculate the Aggregate Impact Value using the formula:
Aggregate Impact Value (%) = (W₂ / W₁) × 100
Where:
W₁ = Original weight of the dry sample
W₂ = Weight of the fraction passing through the 2.36mm sieve -
Repeat Testing
For reliable results, conduct the test at least three times with fresh samples and calculate the average. The average value is reported as the Aggregate Impact Value (AIV) of the material.
• Ensure that the cylindrical cup is clean and dry before each test.
• The tamping of each layer must be uniform to avoid uneven compaction.
• The hammer must fall freely without any hindrance or friction.
• For accurate results, the aggregate sample must be thoroughly dry.
• If the AIV exceeds 30%, additional tests like the Aggregate Crushing Value may be needed.
Interpretation of Results
The Aggregate Impact Value provides valuable insights into the mechanical strength of aggregates. Here's how to interpret the test results:
| Aggregate Impact Value (%) | Classification | Recommended Uses |
|---|---|---|
| Less than 10% | Exceptionally Strong | Heavy-duty concrete floors, high-strength concrete, airport runways |
| 10% - 20% | Very Strong | Highway wearing surfaces, heavy-duty industrial floors, bridges |
| 20% - 30% | Strong | General concrete construction, road base courses, standard pavements |
| 30% - 35% | Satisfactory for Roadwork | Road base and sub-base work, concrete not subject to surface wear |
| 35% - 40% | Weak for Roadwork | Limited use in non-critical applications, sub-bases under controlled conditions |
| Greater than 40% | Too Weak for Roadwork | Not recommended for structural applications, may be used for non-load bearing fills |
Factors Affecting Aggregate Impact Value
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Rock Type
Hard, dense rocks like basalt and granite typically have lower impact values (10-20%) compared to softer rocks like limestone or sandstone (25-40%).
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Moisture Content
Wet aggregates generally show higher impact values than dry ones. This is why the test requires oven-dried samples for standardization.
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Particle Shape
Angular and cubical particles typically perform better under impact than flaky or elongated particles, which tend to break more easily.
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Weathering
Weathered or partially decomposed rocks generally have higher impact values, indicating lower resistance to impact forces.
For critical construction applications, it's recommended to:
• Perform multiple tests (at least three) and use the average value
• Combine AIV results with other tests like Crushing Value and Abrasion Value
• Consider the specific requirements of the project when interpreting results
• Use aggregates with values at least 10% below the maximum allowable limit for added safety
Sample Calculation
Let's walk through a sample calculation for the Aggregate Impact Value test:
Test Data:
| Parameter | Test 1 | Test 2 | Test 3 |
|---|---|---|---|
| Weight of oven-dried aggregate sample (W₁) | 350.0 g | 352.5 g | 349.2 g |
| Weight of aggregate retained on 2.36mm sieve after impact (W₃) | 300.0 g | 298.5 g | 292.1 g |
| Weight of aggregate passing 2.36mm sieve after impact (W₂) | 50.0 g | 54.0 g | 57.1 g |
| Total (W₂ + W₃) | 350.0 g | 352.5 g | 349.2 g |
Calculation for Each Test:
Test 1: Aggregate Impact Value = (W₂ / W₁) × 100 = (50.0 / 350.0) × 100 = 14.29%
Test 2: Aggregate Impact Value = (W₂ / W₁) × 100 = (54.0 / 352.5) × 100 = 15.32%
Test 3: Aggregate Impact Value = (W₂ / W₁) × 100 = (57.1 / 349.2) × 100 = 16.35%
Average Value:
Average AIV = (14.29 + 15.32 + 16.35) / 3 = 15.32%
The calculated Average Aggregate Impact Value of 15.32% falls within the "Very Strong" category (10-20%). This aggregate is suitable for high-quality applications such as highway wearing surfaces, heavy-duty industrial floors, and bridge construction. It exceeds the requirements for general concrete construction and road work.
Using the Aggregate Impact Value Calculator
Our Aggregate Impact Value Calculator automates the entire calculation process, making it convenient and error-free. Here's how it works:
Aggregate Impact Value Calculator
The calculator streamlines the entire process through a user-friendly interface that handles calculations, validates inputs, and provides instant interpretations of results.
Input Data Entry
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Select Test Number
The calculator allows you to perform up to three tests (Test 1, Test 2, Test 3) by selecting the appropriate tab. This follows the standard practice of conducting multiple tests for reliability.
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Enter Total Weight
Input the total weight of your prepared aggregate sample in grams (W₁). This is the weight of oven-dried aggregate placed in the cylindrical cup before impact.
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Enter Weight Retained
Input the weight of aggregate retained on the 2.36mm sieve after impact (W₃). This represents the portion of the sample that remained intact after the test.
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Auto-Calculate Weight Passing
The calculator automatically determines the weight of aggregate passing through the 2.36mm sieve (W₂) by subtracting the retained weight from the total weight (W₂ = W₁ - W₃).
Practical Applications & Specifications
The Aggregate Impact Value test is widely used across various construction sectors with different specification requirements:
Highway Engineering
For highway wearing courses, AIV should not exceed 25% to ensure durability under heavy traffic loads and varying weather conditions.
Railway Ballast
Railway ballast typically requires an AIV below 20% to withstand the dynamic loads and vibrations from train movement.
Structural Concrete
For high-strength structural concrete, aggregates with AIV below 30% are preferred to ensure adequate strength and durability.
Hydraulic Structures
Dams and water-retaining structures typically require aggregates with AIV below 25% to withstand water pressure and prevent deterioration.
Comparison with Other Aggregate Tests
| Test | Purpose | Typical Specifications | Relationship with AIV |
|---|---|---|---|
| Aggregate Crushing Value (ACV) | Measures resistance to crushing under gradually applied compressive load | ≤ 30% for wearing surfaces, ≤ 45% for other concrete | Generally, ACV values are slightly higher than AIV for the same aggregate |
| Los Angeles Abrasion (LAA) | Measures resistance to abrasion and impact in rotating drum | ≤ 30% for high-quality concrete, ≤ 50% for base course | Typically, higher AIV correlates with higher LAA values |
| Ten Percent Fines Value (TFV) | Load required to produce 10% fines | ≥ 100 kN for roadwork, ≥ 50 kN for other applications | Inverse relationship: high TFV indicates low AIV |
| Flakiness & Elongation Index | Measures shape characteristics of aggregate | ≤ 35% for concrete, ≤ 25% for highway surfacing | Flaky and elongated particles typically show higher AIV |
For comprehensive quality assessment, it's recommended to conduct multiple tests rather than relying solely on AIV. The combination of AIV, ACV, and abrasion tests provides a more complete picture of aggregate mechanical properties.
References & Resources
For further information on Aggregate Impact Value testing, refer to the following standards and resources:
- IS:2386 (Part IV)-1963 - Methods of Test for Aggregates for Concrete - Mechanical Properties
- IS:383-2016 - Specification for Coarse and Fine Aggregates from Natural Sources for Concrete
- BS 812-112 - Testing Aggregates - Methods for Determination of Aggregate Impact Value
- MORTH Specifications for Road and Bridge Works
- IRC (Indian Roads Congress) Standards for Highway Materials