Thin White Topping with Estimate Items in SSR and sample Drawings

 White Topping

Important criteria's for choosing white topping

1) Road Structure should be free from distresses occurred in pavements due to failure of Subgrades (Rutting, Potholes etc.)

2) Road Thickness must have at least 75mm of bituminous layer, in such layers BBM, MPM and BUSG such layer thicknesses are not calculated. BM, DBM, Carpet, BC etc. such layers are only considered for thickness calculations.

White topping image 1--> Two lane with Earthen shoulder without footpath

White topping image 2--> Two lane with paved shoulder and footpath cum drain

White Topping image 3--> Layer Details

White Topping image 4 --> Details near Widening Joint

White topping Image 5 --> CC pavement Joints Details

It is suggested that Dowel bars shall be provided only at locations of construction joints (where construction is stopped at the end of the day)

Tie bars shall be coated with protective coating at the centers of bar so that corrosion can be prevented in unembeded  portion of tie bar. 

Items used for estimation:-

Item no.1)   DENSE BITUMINOUS MACADAM: Proving and laying dense bituminous macadam using crushed aggregates of Grading 2, premixed with bituminous binder, transported to site with VTS laid over a previously prepared surface ,finished to the required grade, level, alignment and rolling to achieve the desired compaction for 50/75 mm compacted thickness with 4.5 % VG 30 Bitumen-Using 80 TPH Batch Mix type hot mix plant with SCADA Sensor Paver intelligent compactor with compaction analyzer and VSat attachment including tack coat VG-30 Bitumen @0.25kg/sqm.

Note:- Item 1 should be incorporated in estimate only for profile correction, not for entire length of road.

Roughening of DBM surface is also required so any item similar to milling can be considered.

Item no.2)   White topping of concrete overlay for Urban road M50 Construction of thin white topping plain cement concrete pavement over prepared sub base with 43 grade cement ,coarse and fine aggregate confirming to IS 383 maximum size of coarse aggregate not exceeding 25 mm replacing cement by fly ash to the extent of 15% and sand by and sand by 10%,mixed in a batching and mixing plant as per approved mix design, transported to site, laid with a fixed form or slip form paver, spread, compacted and finished in a continuous operation including provision of contraction, construction and longitudinal joints with panel size of 1mx1m,joint filler, sealant primer, joint sealant, debonding strip, dowel bar, tie rod, admixtures, polypropylene fiber as approved ,curing compound, finishing to lines and grades as per drawing.

Definition :- PCC overlay on the top of an existing Bituminous pavement.

Note:- PCC overlay may or may not be bonded to the layer below.

IRC No.:- IRC:SP:76-2015, GUIDELINES FOR CONVENTIONAL AND THIN WHITETOPPING

Why white topping ??

Rutting of Bituminous pavement is real problem in Indian subcontinent climate (hot, heavy rainfall) with heavy truck loads, operating under frequent start/stop conditions.

Panel Size = 1 m x 1 m to 1.25 m x 1.25 m.

Note:- PCC overlay on existing concrete surfaces, as strengthening/ rehabilitation measure are not called white topping as the existing surface is not Bituminous.

Types of White topping based on degree of bonding between the underlying Bituminous layer with PCC overlay 

1) Bonded interface

2) Unbonded interface 

3) Partial bonded interface 

Type based on Thickness of overlay

1) conventional :- 200 mm or 200+ mm

Can be constructed Without any bond

2) THIN WHITETOPPING (TWT) :- 100 mm < Thickness < 200 mm

Bonding between PCC overlay and Bituminous layer is considered but not mandatory.

Note:- High strength concrete with fibres is commonly used.

Joint spacing --> 0.6 m to 1.25 m

3) Ultra thin white topping (UTWT)

Thickness  <= 100 mm

Bonding is Mandatory 

Milling the existing Bituminous surface to an average depth of 25 mm is used to provide Bonding interface.

Note:- Not recommended for Indian climate conditions.

When white Topping is avoided??

When continuity of subgrade/sub-base support is in doubt.

Fibres :- steel/polypropylene/polyester/polyethylene/nylon

Uniform dispersion in concrete mass.

     Polymeric fibres - 

Length = 30 mm to 60 mm

Dia = 0.2 mm

Dosage = 0.5% to 1.5 % by concrete volume (4.5 to 14 kg/cu.m)

Tolerance in slump :- + or - 15 mm for slump < 50 mm

+ or - 25 mm for slump 50 < 100 mm

Thin white Topping performance can be improved using micro-surfacing, advantages are as follows

Reduction in Road noise

Surface texture improvement , Skid resistant

Protection of concrete from thermal effects

Preventing water penetration in expansion/contraction, longitudinal joints or through cracks.

Microsurfacing Paver Unisurface 8000

Mumbai - Goa Highway micro-surfacing over concrete pavement