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 coarse or medium-grained sand suitable for such applications. If coarse or medium sand is unavailable, a mix design test must be conducted. In cases where fine sand is used, it should contain less than 3% of silt and clay impurities to ensure quality performance.
The technical specifications for sand are outlined in Table 1. This table provides detailed information on sieve analysis, soil debris content, sulfide and sulfate levels, and other impurities that must be avoided.
**Table 1: Sand Technical Requirements**
| Project | Sieve Size (mm) | Square Hole Sieve | Round Hole Sieve | Cumulative Sieve Residue (%) |
|---------|------------------|-------------------|------------------|-------------------------------|
| | | 0.16 | 0.315 | 0.63 | 1.25 | 2.5 | 5.0 | |
| Grain Size Classification | | | | | | | | |
| Zone I | | 100–90 | 95–80 | 85–71 | 65–35 | 35–5 | 10–0 | |
| Zone II | | 100–90 | 92–70 | 70–41 | 50–10 | 25–0 | 10–0 | |
| Zone 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 matter |
*Note: Zone I sand is typically coarse, Zone II is medium with good gradation, and Zone III is fine sand.*
For organic matter testing, a standard solution is prepared by dissolving 2g of tannin powder in 98mL of 10% alcohol, then mixing 2.5mL of this solution with 97.5mL of 3% sodium hydroxide solution. After shaking and standing for 24 hours, the solution is ready for use.
When using gravel (crushed stone) in cement concrete, the material must be hard, clean, and free from weathered or contaminated particles. It should also meet the grading requirements, with a maximum particle size not exceeding 40mm. The technical requirements for crushed stone are detailed in Table 2.
**Table 2: Crushed Stone Technical Requirements**
| Project | Mesh Size (mm) | Accumulated Sieve Residue (%) | Strength | Needle Particle Content (%) | Sulfur and Sulfate Content (%) | Soil Debris Content (%) |
|---------|----------------|-------------------------------|----------|------------------------------|--------------------------------|--------------------------|
| Particles Grading | 40 | 0–5 | | | | |
| | 20 | 30–65 | | | | |
| | 10 | 70–90 | | | | |
| | 5 | 95–100 | | | | |
| Stone Compressive Strength Ratio (%) | | ≥200 | | | | |
| Stone Strength Classification | | ≥3 Level | | | | |
| 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 should be used instead of high-activity ones to prevent adverse reactions in the concrete. The technical requirements for gravel are listed in Table 3.
**Table 3: Gravel Technical Requirements**
| Project | Mesh Size (mm) | Accumulated Sieve Residue (%) | Voidage (%) | Soft Particle Content (%) | Needle Particle Content (%) | Soil Debris Content (%) | Organic Matter Content | Stone Strength Classification |
|---------|----------------|-------------------------------|-------------|---------------------------|-----------------------------|--------------------------|------------------------|-------------------------------|
| 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) | | Not darker than standard solution | | | | | | |
| Stone Strength Classification | | ≥3 Level | | | | | | |
*Note: Crush index value can be used as an alternative to determine stone strength.*
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