Thin White Topping with Estimate Items in SSR and sample Drawings

White Topping

Important Criteria for Choosing White Topping

1. The road structure should be free from distresses caused by subgrade failure (e.g., rutting, potholes, etc.).
2. The existing road must have at least 75 mm of bituminous layer. Layers such as BBM, MPM, and BUSG are not considered in thickness calculation. Only BM, DBM, Carpet, BC, etc., are included.

White Topping – Two lane with earthen shoulder and without footpath

White Topping – Two lane with paved shoulder and footpath cum drain

White Topping – Layer Details

White Topping – Details near Widening Joint

White Topping – CC Pavement Joint Details

Dowel bars shall be provided only at construction joints (end-of-day stops).

Tie bars shall be coated with protective coating at the center to prevent corrosion in the unembedded portion.

Items Used for Estimation

Item No. 1 – Dense Bituminous Macadam (DBM)

Providing and laying dense bituminous macadam using crushed aggregates of Grading 2, premixed with bituminous binder (VG-30 @ 4.5%), transported with VTS, laid with sensor paver, compacted using intelligent compactor – 50/75 mm thickness including tack coat @ 0.25 kg/sqm.

Note: This item should be included only for profile correction, not for the entire road length.

Roughening of the existing DBM surface is required (consider milling item).

Item No. 2 – White Topping (M50 Concrete Overlay)

Construction of thin white topping plain cement concrete pavement (M50) over prepared bituminous surface using 43-grade cement, coarse/fine aggregates (max 25 mm), fly ash (15% cement replacement), sand (10% replacement), mixed in batching plant, laid with fixed/slip form paver, including all joints (1 m × 1 m panels), dowel/tie bars, admixtures, polypropylene fiber, curing compound, etc., as per approved drawing.

Definition & Reference

White Topping: PCC overlay on top of an existing bituminous pavement (bonded or unbonded).

IRC Reference: IRC:SP:76-2015 – Guidelines for Conventional and Thin White Topping

Why White Topping?

Rutting in bituminous pavements is a major issue in India due to hot climate, heavy rainfall, and overloaded trucks with frequent start/stop conditions.

Panel Size: 1 m × 1 m to 1.25 m × 1.25 m

Types of White Topping

• Conventional (>200 mm): Can be unbonded.
• Thin White Topping (TWT, 100–200 mm): Bonding preferred but not mandatory. High-strength fiber-reinforced concrete commonly used. Joint spacing: 0.6–1.25 m.
• Ultra-Thin White Topping (UTWT, ≤100 mm): Bonding mandatory (milling ~25 mm). Not recommended for Indian conditions.

When to Avoid White Topping

When continuity of subgrade/sub-base support is doubtful.

Fibres in Concrete

Steel, polypropylene, polyester, polyethylene, or nylon fibres for uniform dispersion.

Polymeric Fibres: Length 30–60 mm, Diameter 0.2 mm, Dosage 0.5–1.5% by volume (4.5–14 kg/m³)

Slump Tolerance: ±15 mm (slump <50 mm), ±25 mm (50–100 mm)

Micro-Surfacing Over Thin White Topping

Improves performance with benefits:

• Reduced road noise
• Better surface texture and skid resistance
• Protection from thermal effects
• Prevents water ingress through joints/cracks

Microsurfacing Paver Unisurface 8000

Mumbai-Goa Highway – Micro-surfacing over concrete pavement

Reference: IRC:SP:76-2015 for design, construction, and material specifications.