Whitetopping refers to placing a Portland cement concrete overlay on an existing asphalt pavement surface. It can be either bonded or unbonded. Whitetopping provides structural strengthening, is cost-effective, and offers a more sustainable and rapid rehabilitation approach than full reconstruction. Thicknesses can vary from over 200mm for conventional whitetopping to under 100mm for ultra-thin whitetopping. Case studies in Colorado, Texas, and India demonstrated the successful use of thin whitetopping overlays between 150-175mm thick with joint spacings of 1.8-2m to rehabilitate heavily used urban and highway pavements.

1. Using Whitetopping
Overlay on existing pavement
Whitetopping refers to Portland Cement Concrete (PCC) overlay on the top of existing
bituminous pavement surface.
Concrete overlay on existing asphalt pavement can be either bonded or un-bonded.
What does Whitetopping mean?
What is the purpose to use whitetopping?
Whitetopping serves as a viable alternative for pavement rehabilitation. Applicable on
asphalt surface prone to rutting.
Figure: Typical Concrete Overlay on existing pavement. 1

2. Whitetopping
Conventional
Whitetopping
Thin Whitetopping
(TWT)
Ultra-Thin Whitetopping
(UTWT)
Thickness > 200 mm 100 -200 mm < 100 mm
Bonding Unbonded Preferably Bonded Bonded
Advantages
• Provide the structural strength to existing bituminous pavement
• Cost effective
• Sustainable and rapid approach for pavement rehabilitation than full reconstruction
• Offers extended service life.
• Reduces the maintenance and life-cycle cost of pavement.
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3. Construction Practice (IRC: SP: 76-2015)
• Whitetopping is generally constructed as Jointed Plain Concrete Pavement (JPCP).
• Continuous Reinforced Concrete Pavement (CRCP) and Fiber Reinforced Concrete
Pavement (FRCP) have also been practiced in USA since 1970.
• For JPCP & CRCP
 Thickness: 150-250 mm
 Joint Spacing: 4-4.4 m with provision of dowel bars
• Longitudinal steel reinforcement (CRCP): 0.5-0.6%
• Use of white curing compound or white washing on existing bituminous surface.
• White curing compound or white washing of existing surface: minimize the
temperature of existing bituminous layer by preventing the heat build-up, thereby
reducing the absorption of sunlight. Whitewash can be performed by using either the
white-pigmented curing compound or lime slurry.
• Rate of application of curing compound: 2-3 mL/100 cm2
• Paving of concrete at temperature higher than 35°C shall not be done.
General Consideration for Conventional Whitetopping
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4. Pre-Overlay Repair
Conventional Whitetopping
For Conventional Whitetopping, extensive overlay repair is not required. However, condition
of underlying pavement is of utmost important in the case of CRCP.
Repair of existing pavement is significant to avoid localized failure.
Guidelines provided by ACPA 1988 for the preoverlay repair can be used.
General pavement condition Recommended Repair*
Rutting (< 2 in. (50 mm)) None or milling+
Rutting (> 2 in. (50 mm)) Milling or levelling
Shoving Milling
Potholes Filled with crushed stone cold mixture or hot
mixture
Subgrade failure Remove and replace or repair
Alligator Cracking None
Block Cracking None
Transverse Cracking None
Longitudinal Cracking None
Raveling None
Bleeding None
Table: Guidelines for Whitetopping preoverlay repair (ACPA 1998)
Note: * Other factors to consider: adding edge drains, cost of direct placement on unrepaired pavement versus milling, or levelling.
+ consider deeper than standard joint sawing depth in the whitetopping pavement.
Construction Practice (IRC: SP: 76-2015)
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5. Field Evaluation
Field evaluation of pavement comprises of visual distress survey, deflection testing using
Benkelman Beam Method (BBM) or Falling Weight Deflectometer (FWD) and coring.
Surface Preparation
Conventional Whitetopping
Method 1: Direct placement
Existing surface is prepared just by sweeping & concrete overlay is placed directly.
Ruts in the surface are filled with concrete, thus resulting in thicker concrete pavement.
Method 2: Milling
Milling of existing surface is done to obtain uniform surface and remove surface distortion
like cracks on top portions and adjust cross slopes.
Milling depth: 25 to 50 mm.
Method 3: Placement of levelling course
Levelling course of minimum 50 mm bituminous macadam, dense bituminous macadam is
sometimes used to attain uniform surface for levelling.
If rut depth>50 mm, milling shall be preferred as an economical alternative.
Construction Practice (IRC: SP: 76-2015)
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6. Conventional Whitetopping
Method 4: DLC/PCC Levelling Course
PCC/DLC layer levelling and profile correction thickness:
Minimum Thickness: 75 mm
Average Thickness:100 mm
Maximum Thickness:125 mm
For thickness greater than 125 mm, a leaner concrete may be provided in thickness such that over it PCC
or DLC will be minimum 75 mm.
Separation Layer: Impermeable membrane of low density polyethylene (LDPE) or Geotextile (non-woven
polypropylene blanket 0.45 to 0.55 kg/m2).
Geotextile: provides uniform elastic support to concrete overlay, decreases pumping and avert reflective
cracking.
For Joint spacing <12 x PQC thickness, Separation layer shall not be used, even if PQC layer is designed
as un-bounded pavement.
Inlay
Concrete pavement can be used as inlay when a deteriorated lane has to be removed or
replaced.
Inlays are highly effective when the minimum vertical clearance requirements of structure for
example, road over bridge exceeds the existing level of road.
For wet climatic condition and heavy traffic conditions, dowels or reinforced concrete pavements
may be used.
Construction Practice (IRC: SP: 76-2015)
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7. Construction Practice (IRC: SP: 76-2015)
General Consideration for Thin-Whitetopping
Thin-Whitetopping
• TWT is generally preferred when the existing bituminous pavement condition is fair without wide cracks.
• For improved performance: Effective bond between PCC and existing bituminous surface is required.
• Chiselling may also be carried out at location where milling of existing asphaltic surface is difficult.
• Joint spacing: 1 m & 1.5 m may be provided.
• Square joint spacing (e.g. 1 m x 1 m) is preferred.
• In case of rectangular spacing, the ratio of long and short arm shall not exceed 1.2.
• For TWT overlay, minimum thickness of hot mix bituminous pavement (excluding the milled thickness) is
75 mm.
Site suitable for TWT overlay
 Rural roads
 Medium to Moderately heavy volume roads (e.g. major district road, state highway, low traffic national
highway)
 Intersections
 Minor airport pavement
 Toll Plaza
 Heavy density corridors
 Low volume metaled village roads
 Bus bay and truck lay-bye
Distressed material/subgrade or heavily rut surface has to be replaced partially or full by lean concrete (M10)
grade before laying TWT. 7

8. Thin-Whitetopping
Pre-Overlay Repair
Field Evaluation of Existing pavement
An extensive examination of deficiencies in pavement and their possible cause should be
assessed before selecting TWT as an alternative.
TWT overlay is provided for bituminous pavement exhibiting rutting, shoving and similar other
distresses without wide cracks.
Surface Preparation
Milling and cleaning of top of sub-base is to carried out to ensure effective bonding.
If the pavement condition is sound, direct laying of TWT can be done.
Milling of existing bituminous surface is desirable to enhance the bond and remove any
surface distress or distortions.
Lane Closure
At many intersections where lane closure is limited and traffic detouring is not feasible, the use
of TWT overlay provides quick solutions.
Overhead Clearance
Suitable milling of existing surface before TWT overlay helps in mitigating the problem of
mismatching of adjacent shoulder and elevated traffic lanes.
Construction Practice (IRC: SP: 76-2015)
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9. Figure: Stress Diagram in case of Bonded and Un-bonded TWT
• TWT overlay acts as a composite structure.
• To prevent excessive deflection and high vertical strains, joint spacing of 1 to 1.5 m is
recommended for Indian condition.
• Due to the composite action, load stresses are reduced due to shifting of neutral axes near
interface.
• The critical stress location of TWT is the corner location and critical stress is corner
stresses due to load and curling stresses.
• In short TWT panel, edge load and temperature stresses (which causes top-up transverse
cracking in the middle of slab) are not critical.
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10. Construction Steps
Milling
• Milling of asphaltic pavement provides removal of rutting and gives roughened
surface.
• Provides the bonding between new concrete overlay and existing surface.
• Depth of milling: 25-50 mm, depending on the type and severity of distress and the
available thickness of asphalt pavement.
• Roughness at difficult locations: Hand grinding/Light chiseling may also be used.
• Absence of machinery: Profile correction course of bituminous macadam (minimum
50 mm thickness) may be laid over existing bituminous pavement after applying tack
coat so as to achieve net bituminous thickness of 75 mm.
Repairing of existing pavement
• Presence of cracks in plenty indicates subgrade failure, then the pavement shall be
replaced and re-compaction of subgrade is mandatory.
• Locally observed surface cracks shall be repaired or sealed using properly designed
dense bituminous mixes. The top milled surface and repaired surface shall be in level.
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11. Cleaning of the milled surface
The existing surface after milling or profile corrective course is cleaned to ensure proper
bonding between existing surface and new overlay. Following methods can be used:
• Air blasting/vacuum cleaner
• Power brimming
• Water blasting
• Sand blasting
• Chiseling
Placing, finishing, texturing and curling using conventional paving techniques and
materials
• Placement of form work using steel channels or girders. Use of kerb stone as form
work in not recommended.
• Laying of PCC is followed by runner beam construction without disturbing TWT.
• Semi mechanized method, slip form paver or fixed form paver may be adopted.
• Curing compound/water shall be applied twice the normal rate, because of high surface
area to volume ratio of TWT, which results in rapid loss of surface moisture due to
evaporation.
• For skid resistance, texturing shall be done just after the water sheen has disappeared
and just before the concrete becomes non-plastic.
• Texturing for low speed, municipal or urban projects: burlap drag, turf drag, or coarse
broom texture is sufficient.
• Texturing for high-speed interstate: tining provides excellent long-term skid resistance.
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12. Distress in TWT/ Conventional Whitetopping
Cause: Fatigue cracking may be the primary failure mechanism.
Remedy: Full Panel Replacement
Corner Break/Corner Crack
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13. Cause: Late joint sawing, misalignment of dowel bar at construction joints.
Remedy: Make 8-10 mm wide groove along the crack for a depth of 20 mm
and refill with sealant.
Transverse Crack
Distress in TWT/ Conventional Whitetopping
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14. Cause: Use of masonry to raise the utility duct to road level. Improper workmanship and lack of
adequate protection of edges of the utility chamber.
Remedy: Raising of utility chamber shall be re-casted in concrete. Adequate protection of 0.3 m around
the utility duct should be strengthened using nominal steel mesh.
Damaged Utility Crack
Distress in TWT/ Conventional Whitetopping
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15. Cause: Poor workmanship, bent steel formwork during construction and unprotected
concrete edges results in zig-zag longitudinal joint which later opens up and prone to
damage after saw cutting.
Remedy: Use of strong formwork during construction and make sealing groove along the
longitudinal construction joint.
Damaged Longitudinal Joint
Distress in TWT/ Conventional Whitetopping
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16. Cause: Settlement and damage of underlying bituminous layer leads cracking and shattering of concrete
panels.
Remedy: Full depth repair of damages panels.
Shattered Panels
Distress in TWT/ Conventional Whitetopping
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17. Field Studies
Case 1: SH 68, Denver, Colorado
Thin Whitetopping project on Colorado in 1990 was initiated and two 91 m test section was
selected. The existing asphaltic surface for both the location and the pavement condition
after TWT is presented in Table.
Table: Existing asphaltic surface condition and pavement condition after TWT for location 1
and location 2
Parameter Location 1 Location 2
Thickness of existing asphaltic pavement (AC) 90 mm 125 mm
Slab panels used 2 m x 2 m (small panel) 3.7 m x 4 m
Treatment on AC No No
Tie bar and Dowel Bar Not provided Not provided
Pavement condition after 3 year No Deteriorations Cracking was observed
This project was the first project of TWT in Colorado and, thereafter, the use of milling,
joint spacing and pavement response were recorded with strain gauges were practice.
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18. Case 2: SH 121, Wadsworth Boulevard
The test section was a 4-lane divided roadway with ADT = 30,000 vehicle per day (vpd) as of 2001. The design
ADT for 2020 was estimated to be 40,000 vpd and 3.4% truck. For the construction of TWT following
parameters were used:
1. Thickness of concrete overlay: 150 mm
2. Joint Spacing: 1.8 m
3. TWT used : 130000 m2
4. The placement of TWT was completed in 67 days
5. Length of lanes: 5.6 km
6. Compressive strength of Fast-track mix: 17 MPa in 24h.
The construction of TWT was successfully implement over the full width (11.5 m) and full length of the project.
Figure: Placement of concrete for TWT 18

19. Case 3: SH 83, Parker Road
The project was undertaken to provide rehabilitation of 3 km, 6-lane urban highway. TWT overlay of 150
mm was used and the joints were sawed at 1.8 m intervals in both direction.
Estimated ADT: 52,000 vpd
Project duration: 75 working days. However, the project was completed in 65 working days. Total 90,100
m2 of TWT was placed.
Major challenges faced was the construction phasing and traffic control. In addition, maintaining two lanes
of through traffic in each direction and access to all business and residences throughout construction was
specified.
Thus, the constructed was divided into two phases with end crossovers and head-to-head traffic separated
by painted lines and tubular channelizing devices. Speeds were reduced to 72 km/h during construction.
After completion, the intersection was closed from 7:00 Friday until 5:30 am Tuesday.
Figure : Phased constructed TWT section Figure: Completed TWT
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20. Case 4: Pune, India
Existing condition: The existing pavement was in use for 20 to 25 years and consisted of 150-160 mm
bituminous treatment underlain by 250-300 mm WBM layer.
The road serves 5000 state transport buses daily. The existing roads were found to have several utility
arrangements like RCC pipe for drainage, water supply line, electrical cables etc.
Pavement: Length 1.26 km and carriageway width 11 m with 15/18 ROW.
Milling of 50-60 mm of bituminous layer was done to lower the level and create the bond for concrete overlay.
The portions with structural defects and settlements were completely excavated and new layer of hard
moorum, GSB and DLC were provided.
Thickness of TWT: 175 mm
Concrete: M-40
Construction Details:
• Mix Design: M40 with fibrillated polypropylene fibers was used.
• On-site concrete slump was kept below 40 mm.
• Cement content of 420 kg/m3
• Water-cement ratio: 0.37
• Concrete was transported from RMC plant using transit mixer and placed, compacted with screed and
needle vibrators.
• Panel Size : 1 m x 1 m was created by saw cutting joints within 24 h of casting.
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21. • TWT width: 8 m, casting of only 4 m wide concrete was done first.
• The remaining 4 m was casted after complete curing and joint filling of the first 4 m concrete (approx.
after 21 days).
• Dowel Bar: Dowel bars of 25 mm diameter and 250 mm c/c spacing were provided at construction
joints.
• Tie Bar: Tie bars of 12 to 16 mm dimeter and 400 c/c spacing was provided at longitudinal joints i.e. at
the center of road.
• The texturing was completed using locally available brush. The joints were cut for 1/3rd depth within 24
h and curing of concrete was done for 21 days by water ponding method.
• After 21 days, the joints were sealed with polysulphide sealant and the TWT pavement was opened to
traffic.
Figure 19: Constructed TWT pavement in Pune
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22. Thank You
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