In cement concrete projects, it is essential to use clean and hard sand that meets the grading requirements. The fineness modulus of the sand should be 2.5 or higher, indicating a coarser or medium-grained material. If coarse or medium sand is unavailable, a mix design test must be conducted. In such cases, fine sand with less than 3% impurities of silt and clay can be used, provided it passes the required tests.
Table 1 outlines the technical requirements for sand:
| Project | Sieve Size (mm) | Square Hole Sieve (%) | Round Hole Sieve (%) |
|---------|------------------|------------------------|-----------------------|
| | | 0.16 0.315 0.63 1.25 2.5 5.0 | |
| Grain Size | Cumulative Sieve Residue (%) | District I: 100–90 | 95–80 | 85–71 | 65–35 | 35–5 | 10–0 |
| | | District II: 100–90 | 92–70 | 70–41 | 50–10 | 25–0 | 10–0 |
| | | District III: 100–90 | 85–55 | 40–16 | 25–10 | 15–0 | 10–0 |
| Soil Debris Content | ≤3% | - | - |
| Sulfide and Sulfate Content | ≤1% | - | - |
| Other Impurities | No lime, cinder, or organic debris | - | - |
Note: Zone I sand is typically coarse, Zone II is medium, and Zone III is fine. For organic content testing, a standard solution is prepared by dissolving 2g tannin in 98mL of 10% alcohol, then mixing 2.5mL of this with 97.5mL of 3% sodium hydroxide solution and letting it stand for 24 hours.
For gravel (crushed stone), it should be hard, clean, and free from weathering and debris. It must meet grading specifications, with a maximum particle size not exceeding 40mm. Table 2 shows the technical requirements for crushed stone:
| Project | Sieve Size (mm) | Accumulated Sieve Residue (%) |
|---------|------------------|-------------------------------|
| Particle Grading | 40 | 0–5 |
| | 20 | 30–65 |
| | 10 | 70–90 |
| | 5 | 95–100 |
| Strength | 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 materials are preferred over high-activity ones. Table 3 provides additional requirements for gravel:
| Project | Sieve Size (mm) | Accumulated Sieve Residue (%) | Voidage (%) | Soft Particle Content (%) | Needle Particle Content (%) | Soil Debris Content (%) | Organic Matter Content | Stone Strength Classification |
|---------|------------------|--------------------------------|-------------|---------------------------|-----------------------------|--------------------------|------------------------|-------------------------------|
| | 40 | 0–5 | - | - | - | - | - | - |
| | 20 | 30–65 | - | - | - | - | - | - |
| | 10 | 75–90 | - | - | - | - | - | - |
| | 5 | 95–100 | ≤45 | ≤5 | ≤15 | ≤1 | Not darker than standard | ≥3 levels |
Note: Crush index value can be used as an alternative to strength classification.
Proper selection and testing of sand and aggregates are crucial for ensuring the durability and performance of cement concrete structures. Always refer to local standards and conduct necessary tests before finalizing material choices.
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