I. Asphalt Concrete Base: Quality Requirements for Coarse Aggregates
For the asphalt concrete base course, the quality requirements of the coarse aggregates used in the selected asphalt concrete must comply with the standards set for urban road projects, as outlined in Table 1.4.6. These specifications ensure that the aggregates meet the necessary durability, strength, and performance criteria to support long-term pavement integrity.
**Quality Requirements for Coarse Aggregates in Asphalt Concrete Base**
| Index | Asphalt Concrete Base |
|-------|------------------------|
| Stone Crush Value (not greater than %) | 30 |
| Los Angeles Abrasion Loss (not greater than %) | 40 |
| Apparent Density (not less than t/m³) | 2.45 |
| Water Absorption (not greater than %) | 2.0 |
| Adhesion to Asphalt (not less than) | Level 3 |
| Soundness (not greater than %) | 12 |
| Flaky and Elongated Particles (not greater than %) | 20 |
| Washing Method Particle Content (not greater than %) | 1 |
| Soft Stone Content (not greater than %) | 5 |
| Polishing Value (not less than BPN) | 42 |
| Impact Value (not greater than %) | 28 |
| Broken Crushing Area (not less than %) | 40 (for upper, middle, and lower layers) |
*Note: Ruggedness tests may be conducted as required. The stone polishing value, impact value, and other parameters should be referenced according to the "Asphalt Pavement Construction and Acceptance Specifications."*
II. Quality Requirements for Sand Aggregate in Asphalt Concrete Base
In addition to coarse aggregates, the quality of sand used in the asphalt concrete base course must also meet specific standards. The sand should conform to the requirements specified for urban road projects, as detailed in Table 1.4.7. This ensures proper gradation, workability, and compaction of the asphalt mixture.
**Natural Sand Specifications for Asphalt Concrete**
| Square Hole Sieve (mm) | Round Hole Sieve (mm) | Coarse Sand (%) | Medium Sand (%) | Fine Sand (%) |
|-------------------------|------------------------|------------------|------------------|----------------|
| 9.5 | 10.0 | 100 | 100 | 100 |
| 4.75 | 5.0 | 90–100 | 90–100 | 90–100 |
| 2.36 | 2.5 | 65–95 | 75–100 | 85–100 |
| 1.18 | 1.2 | 35–65 | 50–90 | 75–100 |
| 0.6 | - | 15–29 | 30–59 | 60–84 |
| 0.3 | - | 5–20 | 8–30 | 15–45 |
| 0.15 | - | 0–10 | 0–10 | 0–10 |
| 0.075 | - | 0–5 | 0–5 | 0–5 |
| Fineness Modulus (Mx) | - | 3.7–3.1 | 3.0–2.3 | 2.2–1.6 |
*Note: This table is based on the "Asphalt Pavement Construction and Acceptance Specifications."*
These specifications are essential to ensure that both the coarse and fine aggregates contribute to a strong, durable, and well-structured asphalt concrete base. Proper selection and testing of materials are critical to the success of any road construction project.
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