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D5821-13 – Standard Test Method Technical Guide
📋 Overview and Purpose of ASTM D5821-13
ASTM D5821-13 (Reapproved 2017) provides the standard procedure for determining the percentage, by mass or by count, of fractured particles in coarse aggregates. This test is critical for evaluating aggregate quality, as outlined in Section 4.1. The primary purpose of fractured particle requirements is to maximize shear strength by increasing inter-particle friction in bound or unbound mixtures, provide stability for surface treatments, and provide increased friction and texture for pavement surface courses. The standard is issued under the fixed designation D5821 and values stated in SI units are regarded as the standard.
🔍 Fractured Face Criteria and Terminology
Section 3 of the standard defines the essential terminology for this test. A fractured face is an angular, rough, or broken surface created by crushing, by other artificial means, or by nature. Crucially, a face only qualifies if its projected area is at least as large as one-quarter (¼) of the maximum projected area of the particle, and the edges must be sharp or slightly blunt. This explicitly excludes small nicks and minor damage. A fractured particle is then a particle having at least the minimum number of such faces specified (usually one or two).
| 🔍 Criterion | 📐 Requirement |
|---|---|
| Surface Definition | Angular, rough, or broken surface |
| Minimum Projected Area | At least ¼ of the maximum cross-sectional area |
| Edge Condition | Sharp or slightly blunt edges |
| Origin | Crushing, artificial means, or nature |
⚠️ Small Nick Exclusion: According to Section 3.1.1.1, minor chipping or surface damage is not counted. A face is only considered fractured if its projected area meets the strict ¼ rule relative to the maximum cross-sectional area of the entire particle.
⚙️ Apparatus Specifications and Test Data
Section 5 details the required apparatus for this test method. The balance must be accurate and readable to within 0.1 % of the test sample mass at any point within the range of use. Sieves must conform to Specification E11, and sample splitting must follow Practice C702. ASTM D5821-13 also provides clear default criteria for testing when the governing specification is ambiguous.
| 🛠️ Apparatus | ⚡ Specification |
|---|---|
| Balance | Accurate and readable to 0.1 % of test sample mass |
| Sieves | Conforming to Specification E11 |
| Sample Splitter | Suitable for Practice C702 |
💡 Default Calculation Method: If the project specification does not specify the number of fractured faces or whether to use mass or count, Section 4.2 directs the user to default to the criterion of at least one fractured face and calculate the percentage by mass.
❓ Frequently Asked Questions
🔍 What is the minimum size requirement for a face to be considered “fractured”?
The standard explicitly defines this in Section 3.1.1.1. The projected area of the fractured face must be at least one-quarter (¼) of the maximum projected area of the entire aggregate particle. Faces smaller than this are classified as small nicks and are excluded.
⚡ How do I choose between “by mass” and “by particle count”?
The standard allows for either method based on the project specification. If the specification does not state which method to use, ASTM D5821-13 directs the user to default to calculating the percentage by mass and to use the criterion of at least one fractured face.
💡 What is the required accuracy for the balance in Section 5.1?
The balance or scale must be accurate and readable to within 0.1 % of the test sample mass at any point within the range of use. This high degree of precision is critical for generating reliable test data.
📌 Why is the percentage of fractured particles important for performance?
As stated in Section 4.1, the primary purposes are to maximize shear strength by increasing inter-particle friction in bound or unbound aggregate mixtures, provide stability for surface treatment aggregates, and provide increased friction and texture for aggregates used in pavement surface courses.