IRC Code: SP:107-2015 - Guidelines for Gap Graded Wearing Course with Rubberised Bitumen (Bitumen Rubber)

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The use of rubberised bitumen in road construction is a revolutionary approach that enhances durability, flexibility, and sustainability. The IRC Code: SP:107-2015 provides engineering guidelines for the gap-graded wearing course with rubberised bitumen, ensuring stronger and longer-lasting road pavements.

This blog explores the key features of gap-graded bituminous mixes using crumb rubber, their advantages, material composition, mix design, and environmental benefits.

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What is a Gap-Graded Wearing Course?

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A gap-graded wearing course is a bituminous mix with a specific gradation pattern that leaves gaps between aggregates. These gaps allow the incorporation of crumb rubber, which absorbs oil from the bitumen, expands, and makes the mix denser, durable, and more flexible​.

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Why Use Rubberised Bitumen?

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Rubberised bitumen, also known as Bitumen Rubber (BR), is produced by blending crumb rubber from recycled tires with bitumen at high temperatures. This process improves the elasticity, resistance to rutting, and cracking, making it an ideal choice for road surfaces.

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Key Advantages of Rubberised Bitumen

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The IRC: SP:108-2015 highlights multiple benefits of using gap-graded rubberised bitumen mixes:

1. Enhanced Durability – The rubber component increases elasticity and fatigue resistance, reducing cracks and potholes.
2. Higher Load Bearing Capacity – Improves resistance to heavy traffic loads, reducing road maintenance costs.
3. Environmental Sustainability – Utilises discarded vehicle tires, reducing waste in landfills and promoting green construction.
4. Improved Skid Resistance – The gap-graded texture provides better surface friction, enhancing road safety.
5. Reduced Road Noise – Absorbs sound and vibrations, creating a quieter pavement​.

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Composition and Mix Design of Rubberised Bitumen

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1. Materials UsedAccording to IRC: SP:108-2015, the mix consists of:

• Crumb Rubber (sourced from shredded vehicle tires)
• Bitumen (typically VG-30 or VG-40)
• Coarse Aggregates (sized for gap grading)
• Fine Aggregates (sand and mineral fillers)
• Additives (if required, for workability and adhesion)

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2. Mixing Process

1. Crumb rubber is blended with hot bitumen at 180-210°C to activate the rubber.
2. The mixture is stirred continuously to ensure proper dispersion.
3. Aggregates are heated separately and mixed with the bitumen-rubber blend.
4. Compaction is done using rollers to achieve the desired density​.

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3. Performance Criteria

• Marshall Stability – Minimum 1200 kg
• Flow Value – 2-4 mm
• Air Voids – 3-5%
• Bitumen Content – 6-8%

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Environmental Benefits of Using Rubberised Bitumen

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‍One of the major objectives of IRC: SP:108-2015 is to reduce environmental impact by promoting the use of recycled materials.

• Reuses waste rubber tires, reducing landfill accumulation.
• Decreases carbon footprint by replacing some bitumen with rubber.
• Reduces pollution from burning tires, a major environmental hazard​.

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Implementation and Future Scope

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‍Many countries, including India, the USA, and South Africa, have successfully adopted rubberised bitumen in road construction. The IRC: SP:108-2015 encourages wider implementation across national highways and urban roads.Future developments may focus on:

• Optimized mix design for different climatic conditions.
• Further reduction of greenhouse gas emissions.
• Enhanced research on alternative rubber sources.

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Conclusion

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‍The IRC Code: SP:107-2015 serves as a comprehensive guideline for gap-graded wearing courses with rubberised bitumen. With its improved durability, cost-effectiveness, and environmental benefits, this technology is set to transform India’s road infrastructure.

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