Decoding IRC Code 105:1988 – Tentative Specification for Bituminous Concrete in Airfield Pavements

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The IRC Code 105:1988, published by the Indian Roads Congress, outlines the Tentative Specification for Bituminous Concrete (Asphaltic Concrete) for Airfield Pavements. This guideline serves as a foundational document, detailing the materials, construction techniques, and quality controls essential for laying bituminous concrete in airfield pavements. Let’s explore its key elements and practical implications.

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Overview of IRC Code 105:1988

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This specification focuses on designing and constructing bituminous concrete as a durable and stable surface for airfield pavements. Key highlights include:

• Scope: Applicable for surface courses with a single layer up to 50 mm thickness.
• Design Criteria: Includes mix designs based on the Marshall method to ensure optimal stability and durability.
• Application: Ensures compliance with stringent engineering standards for airfield operations.

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Design Criteria: The Backbone of Quality

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The code emphasizes proper mix design to meet stability, durability, and void requirements. As per the Marshall method, the criteria include:

1. Stability: Minimum 820 kg for compacted specimens.
2. Flow: Optimal range between 2 to 4 mm.
3. Voids in Mix: Maintain between 3% to 5%.
4. Binder Content: Ranges from 5% to 7.5%, ensuring cohesion and flexibility.

These criteria aim to provide a robust and lasting surface, capable of withstanding the operational stresses of airfield pavements.

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Material Specifications

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Bitumen

• Must comply with IS: 73-1961 standards.
• Appropriate grades (30/40 to 80/100) are selected based on regional conditions and traffic loads.

Aggregates

• Coarse and fine aggregates should meet physical and gradation requirements, with minimal impurities.
• Filler materials like stone dust or fly ash enhance the mix quality.

Gradation

Two gradation levels (40 mm and 50 mm) are specified to suit different project requirements, ensuring flexibility in design.

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Construction Guidelines

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Preparation and Transport

• The base must be cleaned, leveled, and free from dust or debris before laying bituminous concrete.
• Mixes should be prepared in a hot mix plant and transported in covered vehicles to avoid contamination.

Tack Coat Application

• A tack coat ensures bonding between layers, with specific bitumen application rates depending on the base material.

Spreading and Rolling

• A mechanical paver spreads the mix, followed by systematic rolling to achieve compaction.
• Compaction must reach 98% of the laboratory density to ensure durability.

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Quality Control: Ensuring Perfection

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The IRC Code emphasizes stringent quality control measures:

1. Aggregate Testing: Sieve analysis and physical property tests are mandatory.
2. Temperature Monitoring: Both binder and mix temperatures must remain within prescribed ranges.
3. Field Density Tests: Ensure compaction standards are met.
4. Surface Evenness: Longitudinal and transverse profiles must meet specified tolerances to maintain smoothness.

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Benefits of Adhering to IRC Code 105:1988

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1. Enhanced Durability: Ensures long-lasting pavements with reduced maintenance.
2. Operational Efficiency: Smooth surfaces minimize wear and tear on aircraft.
3. Compliance with Standards: Aligns with national and international engineering practices.

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Conclusion

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The IRC Code 105:1988 is an invaluable resource for engineers working on airfield pavements. By providing clear guidelines on material selection, design, and construction, it ensures the delivery of high-quality and durable infrastructure.

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