IRC Code 129: Specifications for Open-Graded Friction Course (OGFC)

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The IRC Code 129, published by the Indian Roads Congress (IRC) in December 2019, introduces comprehensive guidelines for the design, production, and placement of the Open-Graded Friction Course (OGFC). This bituminous surface layer, developed as early as the 1950s, plays a pivotal role in enhancing road safety and efficiency by improving drainage, reducing hydroplaning, and minimizing tire-pavement noise. Below, we delve into the detailed specifications and significance of OGFC as outlined in IRC Code 129.

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What is Open-Graded Friction Course (OGFC)?

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OGFC is a thin, porous bituminous wearing course applied to impervious surfaces. Its structure consists of interconnected air voids, which facilitate surface drainage, especially during rainfall, thereby reducing the risks of hydroplaning. Additionally, OGFC enhances night-time visibility, reduces splash and spray, and minimizes pavement-tire noise, ultimately improving road safety.

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Key Benefits of OGFC:

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• Improved Safety: Reduces vehicle splash, enhances friction, and prevents skidding.
• Enhanced Visibility: Drains water quickly, improving visibility during wet conditions.
• Noise Reduction: Lowers pavement-tire interaction noise due to its macrotexture.
• Environmental Advantages: When used in shoulders or parking lots, it supports rainwater harvesting.

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Scope of IRC Code 129

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The IRC Code specifies that OGFC layers should be laid on impervious bituminous surfaces to provide skid resistance and drainage. OGFC relies on stone-to-stone contact for load transfer and durability. The scope also includes provisions for experimental trial sections to assess OGFC performance under real-world conditions.

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Materials for OGFC

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1. Bitumen:
   • Should conform to viscosity grade (VG-40) or Polymer Modified Bitumen (PMB) as per IS:15462 or Crumb Rubber Modified Bitumen (CRMB) as per IS:17079.
   • Minimum bitumen content is 5.5% by weight of the mix.
2. Coarse Aggregates:
   • Clean, hard, durable, and cubical-shaped aggregates free from organic or other deleterious substances.
   • Aggregate physical properties include:
     • Los Angeles Abrasion Value: ≤30%
     • Aggregate Impact Value: ≤15%
     • Polished Stone Value: ≥55
3. Fine Aggregates:
   • Manufactured sand or crushed fines passing a 4.75 mm sieve but retained on a 0.075 mm sieve.
   • Should be non-plastic and have a Sand Equivalent Value ≥50.
4. Stabilizers:
   • Pelletized cellulose fibers, dosed at 0.3% of the mix weight, are used to control binder drain-down.

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OGFC Mix Design

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The mix design for OGFC follows the ASTM D7064 standard. Key parameters include:

• Air Voids: 18–22% for adequate permeability.
• Voids in Mineral Aggregates (VMA): Minimum 25%.
• Binder Drain-Down: Should not exceed 0.3%.

Trial gradations are compacted using the Marshall method with 25 blows per face, and the optimum binder content is determined at 20% air voids.

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Production and Placement of OGFC

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1. Mixing:
   • OGFC is mixed in batch or drum plants with provisions to uniformly add stabilizing fibers.
2. Surface Preparation:
   • Existing surfaces are cleaned of debris, and a tack coat (0.23–0.45 kg/m²) is applied.
3. Placement:
   • OGFC is laid in thin layers of 20–40 mm thickness and compacted using static steel rollers.
4. Weather Restrictions:
   • OGFC cannot be placed during rain, fog, or when surface temperatures are below specified thresholds (10°C for bitumen, 15°C for PMB).

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Quality Control and Testing

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IRC Code 129 emphasizes strict quality control during the design, production, and placement of OGFC. Key tests include:

• Drain-Down Test: Ensures binder stability during transportation.
• Cantabro Abrasion Test: Measures the durability of compacted OGFC specimens.
• Tensile Strength Ratio (TSR): Evaluates resistance to moisture-induced damage.

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Experimental Sections

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Before implementing OGFC on larger road networks, trial sections (minimum 150 m) are constructed to evaluate its performance. Parameters such as mix composition, volumetric properties, and compaction patterns are tested to ensure compliance with specifications.

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Conclusion

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The IRC Code 129 is a critical resource for engineers and contractors in road construction. By defining the specifications for OGFC, the code ensures improved road safety, enhanced driving comfort, and sustainable water management. The adoption of these guidelines can significantly elevate the quality of road infrastructure in India.

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