The typical specifications for PCC (Portland Cement Concrete) delivery to paving sites focus on ensuring the concrete maintains its workability and quality during transit. Key requirements include a minimum of 1-2 hours between water introduction and discharge to allow proper mixing and hydration, and a maximum of about 300 drum revolutions between these stages to prevent overmixing or segregation. These parameters help guarantee the concrete's consistency and performance upon arrival at the paving site.
Key Points Explained:
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Time Between Water Introduction and Discharge (1-2 hours minimum)
- This interval ensures adequate hydration and mixing of the concrete before placement.
- Too short a time may result in insufficient mixing, leading to weak or non-uniform concrete.
- Too long a time could cause premature setting or loss of workability, making the concrete harder to place and finish.
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Maximum Drum Revolutions (300 revolutions)
- Limiting drum revolutions prevents overmixing, which can cause segregation (separation of aggregates from the cement paste).
- Excessive mixing may also generate excess heat, accelerating the setting time and reducing workability.
- This specification ensures the concrete remains homogeneous and easy to handle upon discharge.
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Workability and Quality Assurance
- These specifications are designed to maintain the concrete's slump (a measure of consistency) and compressive strength.
- Properly mixed and transported concrete ensures smoother paving operations and long-term durability of the pavement.
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Practical Implications for Paving Sites
- Contractors must coordinate delivery schedules to align with paving progress, avoiding delays that could compromise concrete quality.
- Monitoring drum revolutions and transit time helps prevent rejections or costly reprocessing of non-compliant loads.
By adhering to these specifications, paving projects can achieve efficient placement, optimal performance, and reduced risk of defects.
Summary Table:
| Specification | Requirement | Purpose |
|---|---|---|
| Time Between Water & Discharge | 1-2 hours minimum | Ensures proper hydration and mixing, preventing weak or non-uniform concrete. |
| Maximum Drum Revolutions | ~300 revolutions | Prevents segregation, excess heat, and maintains homogeneity. |
| Workability & Quality Assurance | Maintain slump & strength | Guarantees smooth paving and long-term pavement durability. |
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