I. Asphalt Concrete Base: Quality Requirements for Coarse Aggregates
For the asphalt concrete base course, the quality requirements of the coarse aggregate used in the selected asphalt mix should comply with the standards set for urban road projects, as outlined in Table 1.4.6.
The following are the key quality parameters for coarse aggregates used in asphalt concrete bases:
| 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) | Grade 3 |
| Soundness (not greater than %) | 12 |
| Flaky and Elongated Particle Content (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 |
Note: The soundness test can be conducted as required. The polishing value and impact value should be referenced according to the "Asphalt Pavement Construction and Acceptance Specifications."
II. Quality Requirements for Sand Aggregate in Asphalt Concrete Base
For the asphalt concrete base course, the quality requirements for sand used in the selected asphalt mix should also follow the standards of urban road projects, as specified in Table 1.4.7.
The following table outlines the specifications for natural sand used in 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."
When selecting aggregates for asphalt concrete, it's essential to ensure that all materials meet the required performance criteria to guarantee the durability, stability, and safety of the pavement. Proper testing and adherence to these standards help prevent premature failure and reduce long-term maintenance costs.
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