IRC Code: Specifications for Mix Seal Surfacing (MSS) & Close-Graded Premix Surfacing (CGPS) (IRC:SP:78-2008)

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Mix Seal Surfacing (MSS) and Close-Graded Premix Surfacing (CGPS) are essential surface treatments for flexible pavements, offering durability, skid resistance, and cost-effectiveness. The Indian Roads Congress (IRC) introduced IRC:SP:78-2008, which provides detailed specifications for these surfacing methods, ensuring high performance in low-traffic and high-rainfall areas.

In this blog, we will explore the scope, materials, construction techniques, and quality control aspects of this IRC code.

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What is IRC:SP:78-2008?

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The IRC:SP:78-2008 manual was introduced to standardize Mix Seal Surfacing (MSS) and Close-Graded Premix Surfacing (CGPS), which are used as wearing courses on prepared granular or bituminous bases. This surfacing method is preferred for low-volume roads (up to 10 million standard axles or MSA) and offers better resistance to water infiltration, skid resistance, and surface durability.

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Key Features of the IRC Code (IRC:SP:78-2008)

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✅ Suitable for low-traffic roads (up to 10 MSA).
✅ Ideal for high-rainfall and water-prone areas.
✅ Provides enhanced skid resistance.
✅ Ensures better bonding with bituminous layers.
✅ Prevents surface disintegration and enhances road life.

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Scope of IRC:SP:78-2008

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According to the IRC guidelines, Mix Seal Surfacing (MSS) and CGPS are designed for low-volume traffic roads and act as a cost-effective alternative to dense bituminous macadam (DBM) or semi-dense bituminous concrete (SDBC).

✔ Thickness: 20mm
✔ Base Requirement: Well-prepared granular or bituminous layer
✔ Two Types of Surfacing:

• Type A: Suitable for high-rainfall areas
• Type B: Suitable for low-rainfall areas (less than 150 cm per year)

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Materials Used in MSS & CGPS (As per IRC:SP:78-2008)

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1. Bituminous Binder

The binder used for Mix Seal Surfacing (MSS) should conform to the standards set by the Bureau of Indian Standards (BIS) or IRC:SP:53. The selection of viscosity-graded (VG) paving bitumen depends on climatic conditions:

Bitumen GradeApplicationVG-40High-stress areas like intersections, toll boothsVG-30Most common, used in moderate climatesVG-20Cold climates, high-altitude regionsVG-10Spraying and cold-weather applications

For tack coat, rapid-setting cationic bitumen emulsion (IS:8887) is preferred.

2. Aggregates

The aggregates used in MSS/CGPS should be crushed stone or gravel that meets specific strength and durability standards.

✔ Aggregate Impact Value: ≤ 30%
✔ Los Angeles Abrasion Value: ≤ 40%
✔ Flakiness Index: ≤ 25%
✔ Water Absorption: ≤ 1%
✔ Adhesion to Bitumen: Minimum 95% retained coating

The aggregate grading should conform to Type A (for high rainfall) or Type B (for low rainfall) as defined in the IRC:SP:78-2008 manual.

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Construction Process of Mix Seal Surfacing (MSS)

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The construction of MSS/CGPS involves several critical steps to ensure proper bonding and durability.

1. Weather Limitations

🚫 MSS/CGPS should not be laid during rainy weather or when the temperature is below 10°C.

2. Surface Preparation

✔ The base layer should be free of dust, moisture, and foreign materials.
✔ Potholes and depressions should be repaired before applying MSS.
✔ Tack Coat should be applied to enhance bonding with the existing surface.

3. Mixing and Laying

✔ The bituminous mix should be prepared in a hot mix plant or batch mixer.
✔ The binder temperature should be 140-170°C, depending on the bitumen grade.
✔ The aggregates must be uniformly coated with the bitumen before application.

Bitumen GradeMixing Temp (°C)Laying Temp (°C)Rolling Temp (°C)VG-40160-170150100VG-30150-16514090VG-20145-16513585VG-10140-16013080

4. Spreading and Compaction

✔ The mix is spread using mechanical pavers to achieve uniform thickness.
✔ Rolling is done using 8-10 tonne rollers to ensure compaction and surface smoothness.
✔ The road is opened to traffic after the surface cools down to ambient temperature.

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Quality Control Measures

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To ensure long-term durability, strict quality control must be maintained.

✔ Surface Smoothness: No variation greater than 6mm under a 3m straight edge.
✔ Bitumen Content: Must be precisely measured to avoid premature failure.
✔ Aggregate Gradation: Must comply with IRC standards to maintain skid resistance.
✔ Temperature Control: Proper heating of bitumen and aggregates to ensure uniform mixing.

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Advantages of Mix Seal Surfacing (MSS) & CGPS

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✅ Cost-Effective: Uses less bitumen and aggregates compared to other surfacing techniques.
✅ Suitable for Low-Traffic Roads: Ideal for rural and semi-urban roads.
✅ High Skid Resistance: Enhances road safety in wet conditions.
✅ Prevents Water Infiltration: Reduces surface deterioration due to rain.
✅ Faster Construction: Can be laid quickly with minimal road closures.

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Conclusion

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The IRC:SP:78-2008 code for Mix Seal Surfacing (MSS) and Close-Graded Premix Surfacing (CGPS) provides clear guidelines for constructing durable, cost-effective, and skid-resistant road surfaces. By following the specified material selection, construction techniques, and quality control measures, contractors and engineers can enhance the longevity of flexible pavements. For low-volume roads, MSS and CGPS serve as affordable yet effective solutions to improve road performance and reduce maintenance costs.

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