Determination Of Angularity Number Lab Report
Understanding the shape and surface characteristics of aggregate materials is crucial in civil engineering, especially when it comes to pavement construction. Among the various tests used to evaluate aggregate properties, the determination of angularity number is one of the key procedures that help assess how angular or rounded aggregate ptopics are. This lab test provides essential information about the suitability of aggregates in bituminous mixes, where angular ptopics are often preferred for better interlocking and stability.
Objective of the Experiment
The primary objective of the angularity number test is to determine the angularity number of a given sample of coarse aggregates. This value indicates the degree of angularity, which affects the compactability and stability of the aggregate in various construction applications.
Importance of Angularity in Aggregates
Influence on Workability and Strength
Aggregates with a higher angularity number tend to have more edges and corners, leading to better interlocking properties. This is advantageous in bituminous mixtures and concrete where a stable structure is required. However, highly angular aggregates can reduce workability in fresh concrete and require more cement paste or asphalt binder.
Effect on Compaction
Round aggregates compact more easily, which may be desirable in certain applications, but they provide less frictional resistance. On the other hand, angular aggregates resist movement, providing higher shear strength and resistance to deformation in pavements.
Apparatus Required
- Metal cylinder of standard dimensions (usually 3 liters)
- Weighing balance (accurate to 1 gram)
- Aggregates (clean and dry)
- Measuring cylinder or graduated container
- Tamping rod (optional)
Test Procedure
Sample Preparation
The aggregates used for the test should be clean, dry, and conform to the standard size range specified in the guidelines. Typically, 12.5 mm to 10 mm size aggregates are used.
Step-by-Step Method
- Fill the standard metal cylinder with aggregate in three layers, ensuring each layer is poured without compaction or tamping.
- Once the container is full, level the surface gently without pressing down.
- Weigh the container with aggregates and record the weight.
- Determine the volume of the container in cubic centimeters (cc).
Calculation of Angularity Number
The angularity number is calculated using the formula:
Angularity Number = (67 W / V) Ã 100
Where:
- W= weight of aggregate in grams
- V= volume of the container in cc
The standard reference density for perfectly rounded aggregates is taken as 67 grams per 100 cc. Any deviation from this value indicates the degree of angularity.
Observations and Data Recording
Example Data Table
| Parameter | Value |
|---|---|
| Weight of empty container (W1) | 500 g |
| Weight of container + aggregate (W2) | 1350 g |
| Weight of aggregate (W = W2 – W1) | 850 g |
| Volume of container (V) | 1250 cc |
| Angularity Number | (67 850/1250) Ã 100 = 0.2 |
Result
The calculated angularity number in the example above is 0.2. A higher angularity number typically indicates more angular ptopics. Generally, the angularity number for aggregates ranges from 0 (perfectly rounded) to 11 (highly angular).
Discussion
Interpretation of Results
The angularity number helps in determining whether the aggregate will provide sufficient friction and interlock in concrete or bituminous layers. In flexible pavements, angular aggregates are preferred for surface courses, while sub-base layers may use slightly more rounded aggregates for ease of compaction.
Limitations and Accuracy
The method assumes a standard density for rounded aggregates, which may not apply to all rock types. Also, care must be taken during sampling and measurement to avoid errors caused by moisture, compaction, or misreading volumes.
Applications of Angularity Number
- Design of hot mix asphalt (HMA)
- Concrete mix proportioning
- Evaluation of pavement layer materials
- Comparative analysis of aggregate sources
Precautions
- Ensure aggregates are completely dry before testing.
- Do not compact the material while filling the container.
- Use clean and standardized measuring equipment.
- Take multiple readings for better accuracy and consistency.
The determination of angularity number is a simple yet essential test in understanding the characteristics of coarse aggregates. It provides insight into the shape and packing ability of the ptopics, which directly impacts the performance of concrete and bituminous mixes. By measuring how angular the ptopics are, engineers can make informed decisions about the type of aggregates to use in specific construction applications. The test also helps in quality control and selecting materials that contribute to long-lasting and stable pavement structures.
Recommendations
- Use this test in conjunction with other aggregate tests such as shape index and flakiness index for comprehensive analysis.
- Update test records regularly to compare materials from different quarries or suppliers.
- Apply the results in mix design software for accurate prediction of pavement performance.
Through consistent testing and analysis of the angularity number, civil engineers can optimize material selection and ensure the reliability and longevity of infrastructure projects.