PQC concrete stands for Pavement Quality Concrete, a high-strength cement concrete used as the top structural layer in rigid pavement roads. PQC concrete is specially designed to carry heavy traffic loads from trucks, buses and airport vehicles while maintaining long service life. Because of its durability and resistance to deformation, PQC concrete is widely used in highways, expressways, industrial areas and airport runways where ordinary concrete cannot perform efficiently.
How PQC Concrete Works in Pavement
When vehicles move over a PQC concrete surface, the load spreads across the concrete slab rather than penetrating deep into the soil. This slab action reduces stress on the subgrade and prevents rutting. The concrete gains strength through proper mix design and curing, while dowel bars and tie bars transfer load between slabs and control cracking caused by temperature changes. As a result, the pavement remains stable for decades with minimal maintenance.
Layers Below PQC Concrete
Dry Lean Concrete (DLC) Layer
A low cement concrete layer placed directly below PQC. It provides uniform support and prevents pumping of fine particles from soil.
Granular Sub-Base (GSB)
This drainage layer allows water to escape and improves load distribution.
Subgrade
Well compacted natural soil supporting the pavement structure. Good compaction prevents settlement and cracking.
Materials Used in PQC Concrete
High quality materials are required because the entire pavement strength depends on this layer:
- Ordinary Portland Cement for strength
- Crushed aggregates for load resistance
- Clean sand for workability
- Water for hydration
- Admixtures for workability and durability
Steel dowel bars and tie bars are installed at joints to transfer wheel loads and maintain slab alignment.
Construction Process of PQC Concrete
Construction begins after preparation of DLC surface. A slip form paver places the concrete continuously to maintain level and thickness. Vibrators compact the mix and remove air voids. Surface texturing is done to provide skid resistance. Transverse and longitudinal joints are cut to control shrinkage cracks. Proper curing using water or curing compound is done for about 14 days to achieve required strength before opening to traffic.
Common Defects in PQC Concrete
Although strong, poor construction practices may create problems:
- Cracking due to improper curing
- Faulting at joints from weak base support
- Spalling at edges due to heavy impact
- Scaling caused by freeze-thaw action
Quality control during mixing and curing prevents most of these issues.
Advantages of PQC Concrete
PQC concrete is preferred in heavy duty pavements because:
- Very long service life (20–40 years)
- Excellent load carrying capacity
- Resistant to water and fuel damage
- Low maintenance cost
- Suitable for heavy traffic corridors
Disadvantages of PQC Concrete
Some practical limitations exist:
- High initial construction cost
- Requires skilled workmanship
- Longer construction and curing time
- Repair requires traffic diversion
PQC Concrete vs Normal Concrete
| Feature | PQC Concrete | Normal Concrete |
|---|---|---|
| Strength | High | Moderate |
| Application | Roads & runways | Buildings |
| Durability | Very high | Medium |
| Traffic Resistance | Heavy traffic | Light load |
| Maintenance | Low | Moderate |
Maintenance Practices
Joint sealing prevents water entry and pumping. Diamond grinding restores smoothness when roughness increases. Regular inspection ensures long pavement life and prevents expensive reconstruction.
Design Considerations Engineers Use
Engineers design PQC concrete based on traffic load, temperature variation and soil strength. Expansion joints allow thermal movement while reinforcement controls cracking. Proper drainage is critical because trapped water weakens the support layer and causes faulting.
FAQs About PQC Concrete
What is the thickness of PQC concrete
Typically ranges between 250 mm to 350 mm depending on traffic load.
Why is DLC provided below PQC
It gives uniform support and prevents soil particles from pumping into joints.
How long does PQC concrete last
Generally 20 to 40 years with proper joint maintenance.
Is PQC concrete used in village roads
Usually not, because its cost is high and it is meant for heavy traffic roads.
Conclusion
PQC concrete is a high strength pavement material designed for long lasting rigid roads carrying heavy traffic. Its slab action distributes load efficiently, reducing stress on soil and minimizing maintenance needs. With proper construction, curing and joint maintenance, PQC concrete provides durable and reliable performance for highways, expressways and airport pavements for decades.
