Use of Whitetopping Technology for Rehabilitation/Strengthening of National Highways

Based on the Circular from the Ministry of Road Transport & Highways, Government of India, dated 3rd October 2024 (File No. RW/NH-35083/09/2024-S&R (P&B))

Introduction

India currently has approximately 1.46 lakh km of National Highways (NH) network. As the country expands its 2/4/6/8-lane NHs and Expressways, the aging infrastructure requires rehabilitation to extend its service life. Flexible pavements, primarily bituminous, form the largest component of this network. Whitetopping (WT) is one of the rehabilitation techniques, involving a concrete overlay on existing in-service bituminous pavements.

Advantages of Whitetopping Technology

• Extends pavement lifespan by 20-25 years.
• Requires fewer lane closures during the design period.
• Lower life-cycle costs compared to bituminous overlays.
• Durable wearing course in high rainfall regions.
• Concrete's light color reflects more light, reduces urban heat island effect, improves safety, and lowers energy requirements for lighting.
• Fuel consumption on concrete roads is lower than on bituminous roads.

Life-Cycle Cost Comparison (Conceptual Graph)

The following bar graph illustrates a conceptual comparison of life-cycle costs between bituminous overlay and whitetopping, based on typical industry data (hypothetical values for demonstration).

Types of Whitetopping

According to IRC:SP:76 "Guidelines for Conventional and Thin Whitetopping":

• Conventional Whitetopping (Unbonded): Thickness > 200mm, suitable for badly damaged pavements, designed per IRC:58 and IRC:15.
• Thin Whitetopping (TWT): Thickness ≥100mm and ≤200mm, constructed for bonded condition but designed without bond for safety.
• Ultra-Thin Whitetopping (UTWT): Thickness <100mm, bonded interface, not suitable for NHs.

TWT is the most suitable for National Highways.

Selection Criteria for Thin Whitetopping (TWT)

Clause 1.5 and 6.3 of IRC:SP:76 emphasize ensuring subgrade/subbase continuity and fair condition of the existing bituminous surface. TWT is preferred in specific cases after evaluating measurable parameters.

Road Section Selection

Road sections meeting any of the following:

• Bypassed NH sections to be de-notified and handed over after one-time improvement.
• NH sections where lane addition is not envisaged for at least 20 years.
• NH sections through National Parks/Wildlife Sanctuaries/Protected Forests with no lane addition for 20 years and requisite approvals.
• NH sections not responding to bituminous overlays due to re-rutting or recurrent disintegration/reflection cracking from high rainfall/temperature/axle loads.

Evaluation Parameters

Sections must satisfy all:

Parameter	Criteria
Surface Disintegration	Cracked and patched area ≤20%. Cracking limited to wearing course.
Surface Deformation	Mean Rut Depth ≤20mm; single value ≤40mm.
Roughness	≤4000mm/km.
Bituminous Layer Composition	>125mm.
Base and Subbase Composition	≥300mm (granular) or ≥200mm (stabilized).
CBR of In-situ Subgrade	4-days soaked CBR ≥5.0% at field dry density.
Characteristic Deflection	≤1.8mm (Benkelman Beam).
Level Raising	Not more than TWT thickness +50mm.
Traffic Diversion	Possible for min. 14 days (preferably 28 days) post-laying.

Selection Process Flowchart

graph TD A[Start: Identify NH Section] --> B{Meets any Road Section Criteria?} B -->|No| C[Not Suitable for TWT] B -->|Yes| D{Evaluate All Parameters?} D -->|No| C D -->|Yes| E[Suitable for TWT] E --> F[Proceed to Design & Construction]

Good Design and Construction Practices

Adhere to IRC:SP:76, plus best practices:

• Use 4-days soaked CBR in Figs 1 & 2 of IRC:SP:76; post-milling bituminous thickness considered.
• Bond and uniform level: Mill existing surface to 20-50mm depth (cold milling), clean thoroughly. Post-milling bituminous ≥100mm. Level if needed with DBM/BC.
• Pre-overlay Repair: Treat cracks/settled portions by removal and redevelopment. If good condition (cracks <5%, ruts <10mm), use 30-40mm BC or 50mm DBM instead of milling.
• Mist Surface: Maintain <35°C, mist to saturated surface dry.
• Design Thickness: Typically 180-200mm for NHs, may vary with traffic.
• Laying: Full width in single pass with same camber/crossfall.
• Panel Size: Preferably 1.0m x 1.0m, max 1.25m x 1.25m.
• Wind Velocity: If >15km/hr, arrange protections against shrinkage cracks.
• Fibers: Add polypropylene fibers 0.9kg/m³; increase cement ~5%, superplasticizer dosage.
• Curing: Wax-based compound on all surfaces; cover with hessian, moist cure 14-28 days.
• Joints: Dowelled transverse at construction joints; tied longitudinal at center (>6m width).
• Sawing: Within 4-12 hours; two stages (large slabs then small); depth 1/3 of TWT, width 3-5mm.
• Sealing: If high rainfall (>2000mm/annum), seal initial cuts.
• Shoulder: Level earthen drop-off post-overlay.
• Opening to Traffic: After 80% concrete strength.
• Post-Construction Roughness: ≤2200mm/km.

Joint Sawing Process Flowchart

graph TD A[Start: Concrete Laid] --> B[Wait 4-12 Hours Joint Sawing Window] B --> C[Initial Sawing: Large Slabs e.g., 3m x 3m] C --> D[Further Sawing: Small Slabs 1m x 1m] D --> E[Depth: 1/3 TWT Thickness; Width: 3-5mm] E --> F[End: Seal if High Rainfall]

Characteristic Deflection Formula

Characteristic Deflection (D) using Benkelman Beam: Typically calculated as the mean deflection plus two standard deviations for conservative design.

D = μ + 2σ

Where μ is mean deflection, σ is standard deviation. Must be ≤1.8mm.

Conclusion

This circular mandates compliance for using TWT in NH rehabilitation, issued with approval of Competent Authority. It aims to promote durable, cost-effective solutions for India's aging highway network.