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In cement concrete projects, sand must be clean, hard, and meet the grading requirements specified in the standards. The fineness modulus of the sand should be 2.5 or higher, indicating a coarser or medium sand type. If coarse or medium sand is unavailable, a mix design test is required. However, if fine sand with less than 3% silt and clay impurities is available, it can be used after proper evaluation.
The technical specifications for sand are detailed in Table 1 below:
**Table 1: Sand Technical Requirements**
| Project | Screen Size (mm) | Square Hole Sieve | Round Hole Sieve |
|---------|------------------|-------------------|------------------|
| | | 0.16 | 0.315 | 0.63 | 1.25 | 2.5 | 5.0 |
| | | | | | | | |
| **Grading Zone I** | Cumulative Sieve % | 100–90 | 95–80 | 85–71 | 65–35 | 35–5 | 10–0 |
| **Grading Zone II** | Cumulative Sieve % | 100–90 | 92–70 | 70–41 | 50–10 | 25–0 | 10–0 |
| **Grading Zone III** | Cumulative Sieve % | 100–90 | 85–55 | 40–16 | 25–10 | 15–0 | 10–0 |
| Soil Debris Content (%) | - | ≤3 | - | - | - | - | - |
| Sulfide and Sulfate Content (%) | - | ≤1 | - | - | - | - | - |
| Other Impurities | - | - | - | - | - | - | Do not contain lime, cinder, or organic debris |
**Note:**
1. Zone I sand is generally coarse, Zone II is medium to slightly coarse, and Zone III is fine.
2. To prepare an organic matter standard solution, dissolve 2g of tannin powder in 98mL of 10% alcohol, then mix 2.5mL of this solution with 97.5mL of 3% sodium hydroxide solution. Shake well and let it stand for 24 hours before use.
For gravel (crushed stone), it should be hard, clean, and free from weathered or contaminated materials. The maximum particle size should not exceed 40mm. The technical requirements for crushed stone are outlined in Table 2.
**Table 2: Crushed Stone Technical Requirements**
| Project | Mesh Size (mm) | Accumulated Sieve Residue (%) |
|---------|----------------|-------------------------------|
| Particles Grading | 40 | 0–5 |
| | 20 | 30–65 |
| | 10 | 70–90 |
| | 5 | 95–100 |
| Compressive Strength Ratio (%) | - | ≥200 |
| Stone Strength Classification | - | ≥3 levels |
| Needle Particle Content (%) | - | ≤15 |
| Sulfur and Sulfate Content (%) | - | ≤1 |
| Soil Debris Content (%) | - | ≤1 |
**Note:** Stone strength classification should follow the "Highway Engineering Stone Test Regulations."
For gravel aggregates, non-reactive aggregates are preferred over high-activity ones. The technical requirements for gravel are shown in Table 3.
**Table 3: Gravel Technical Requirements**
| Project | Mesh Size (mm) | Accumulated Sieve Residue (%) |
|---------|----------------|-------------------------------|
| Particles Grading | 40 | 0–5 |
| | 20 | 30–65 |
| | 10 | 75–90 |
| | 5 | 95–100 |
| Voidage (%) | - | ≤45 |
| Soft Particle Content (%) | - | ≤5 |
| Needle Particle Content (%) | - | ≤15 |
| Soil Debris Content (%) | - | ≤1 |
| Organic Matter Content (Colorimetric Method) | - | Not darker than standard solution |
| Stone Strength Classification | - | ≥3 levels |
**Note:** Crush index value can be used to assess stone strength.
By following these guidelines, construction projects can ensure the quality and durability of concrete by using properly graded and clean aggregates.
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