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Paper No. 538

WHITETOPPING - A COST-EFFECTIVE REHABILITATIONALTERNATIVE FOR PRESERVING BITUMINOUS PAVEMENTS ON

LONG-TERM BASIS†

V.K. SINHA*, SATANDER KUMAR** & R.K. JAIN***

ABSTRACT

Use of Whitetopping as a rehabilitation measure by strengthening of deteriorated bituminous pavements is increasing.This concept has so far not found significant applications in the country. The Paper attempts to bring forth the concept ofWhitetopping. The brief literature review presents the cost-effectiveness of whitetopping as practiced in the developedworld. The analysis with typical designs of different types of whitetopping has been presented in the Paper to acquaint theengineers at large about the design methods, which could be adopted in the country. The actual cost savings per kilometrewise in case of Ultra-thin & Thin Whitetopping are demonstrated. The Paper concludes based on analysis that Whitetoppingwith the thickness between 100 mm to 250 mm can be used in rehabilitating our large network of existing bituminous roadshaving low to moderate traffic. It is suggested that some pilot projects be done to further the emerging concept of whitetoppingin the country.

1. INTRODUCTION

The focus today is on the construction of long-termperforming pavement, since pavements are the costliestcomponent of Highways. Most of our roads havebituminous pavements with thin binder course. Onlyrecently under NHDP bituminous pavements with thickerbinder courses are being constructed. Bituminouspavements are showing early sign of distressesworldwide, due to increasing loads, intensity of traffic,high tyre pressure etc. The rutting, cracking and ageingetc are quite common. Reflective cracking is anotherform of distress in bituminous overlay. These distressesget more pronounced in hot climatic regions like India,since bitumen is highly sensitive to temperature.Performance of bituminous pavements in hot climaticregions is thus becoming somewhat doubtful. Concreteon the other hand is known to be a relatively stiffermaterial and is relatively less sensitive to hightemperature. Accordingly, concrete pavements are beingincreasingly adopted as an alternative to traditionalbituminous pavements. Even in terms of rehabilitationand repair the use of concrete is replacing traditionalbituminous overlay because of better performance againstrutting and cracking. This is the current internationaltrend.

Earlier, objection against the adoption of concretepavement was that its repair is complex and difficult. It

was wrongly believed that even in case of small distress,the entire road has to be dismantled and reconstructed.With the present growth of technology, all thesemisconceptions are gradually vanishing. PCC overlaysare being provided even on concrete pavements, similarto bituminous pavements. Repair of concrete pavementis also not that difficult now. Concrete pavements areknown to have lasted in the developed world for about40 to 50 years.

Most of our bituminous pavements today, which arebadly suffering from distresses like rutting, shoving,cracking etc are overdue for rehabilitation/strengthening.This will involve huge cost and consumption of scarcephysical resources like aggregates and bitumen. Cost-effectiveness of PCC overlays (whitetopping) vis-a-visbituminous overlay, therefore, needs to be examined.Whitetopped roads on average have proved to be quitecost- effective besides giving an additional life of 20 to30 years on average. The present Paper, which is aconcept Paper, examines the concept of whitetoppingas a cost-effective alternative to bituminous overlays.

2. REMEDY FOR DISTRESS IN BITUMINIOUSPAVEMENT BY WHITETOPPING

Rutting is a common distress observed on bituminouspavements. It is a common experience that once ruttingoccurs on a bituminous pavement, placing a bituminous

* Secretary General, IRC } E-mail: [email protected]**Scientist, CRRI New Delhi. } E- Mail: [email protected]*** Chief Engineer (Retd.) Haryana PWD† Written comments on this Paper are invited and will be received upto 31st December, 2007

224 SINHA, KUMAR & JAIN ON

overlay does not prevent its recurrence. Ruttingreappears soon after the overlay. This is becausebituminous overlay cannot be properly compacted in suchwheel ruts and such overlays are not capable to standup against today’s high tyre pressure and traffic loads.On the contrary, concrete can uniformly fill such rutsand correct the surface profile. Concrete has muchgreater stiffness compared to bituminous overlay and,therefore, reflective cracking (quite common withbituminous overlays) are either eliminated or reducedsubstantially with concrete overlays. Bituminous mixesare sensitive to temperature. They are, therefore, quiteamenable to plastic flow, which leads to distresses liketransverse corrugation and localised bulging (shoving)caused by horizontal vehicle force. These distressesare quite common in case of bituminous overlays at theintersections, at round-abouts and at check-posts, dueto frequent stop/start condition of heavy vehicles. Theydo not occur with concrete overlays. This is becauseconcrete does not exhibit plastic flow.

Concrete is less affected by seasonal weakening ofthe sub-grade since it distributes the load on a widerarea through beam action. A study of test pavement atthe AASHO Road Test (1962) has established thatseasonal variations have much less effect onperformance of concrete pavements than on bituminouspavements. Nearly 61 per cent of the bituminous testsection failed during spring months compared with just5.5 per cent of the concrete section in USA vide Fig.1.Some of the States in USA restrict the heavy loads duringspring months vide Fig.2, even though enforcement isdifficult. Concrete pavement is resilient throughout theentire year. Bituminous pavements/overlays are relativelymore sensitive to heavy loads as compared to concrete.

Fig. 1. Weakening of asphalt roads during spring months.AASHO Road Test Source: ACPA EB210.02P

Fig. 2. Load restrictions used in 19 states (USA) duringthe spring season Source: ACPA EB210.02P

3. CURRENT TREND IN PCC OVERLAYS

According to NCHRP synthesis 204 (1), in USA about708 projects involving concrete resurfacing have beenprovided until 1993. Out of which, 189 projects are onexisting bituminous pavement i.e. Whitetopping. Tables1 to 3 give the trend in PCC overlays till 1993 in USA.

Source: NCHRP Synthesis 204

TABLE1. NUMBER OF CONCRETE RESURFACING BY TYPE AND USE

TYPE (a) Highways Streets Airfields TOTAL

JPCP 319 38 119 476

JRCP 99 24 6 129

CRCP 57 1 9 67

FCP 6 8 18 32

PCP 2 - 2 4

Totals 483 71 154 708

HIGHLIGHTS OF THE 178TH COUNCIL MEETING 225WHITETOPPING - A COST-EFFECTIVE REHABILITATION ALTERNATIVE FOR PRESERVING BITUMINOUS

PAVEMENTS ON LONG-TERM BASIS

(a)JPCP = Jointed Plain concrete PavementJRCP = Jointed Reinforced Concrete PavementCRCP = Continuously Reinforced Concrete

PavementFRC = Fiber Reinforced ConcretePRC = Prestressed ConcreteAC/F = Asphalt Concrete (Bituminous)

CPR = Concrete Pavement Restorations

In Indian context whitetopping has a larger role infuture rehabilitation of the weak bituminous pavements.Advantage of whitetoping is its longer life compared tobituminous overlays, which is known to suffer earlydistress due to material related problems. Table 4demonstrates low initial cost of PCC repair/rehabilitationcompared to bituminous overlays as per the experiencein USA.

TABLE 2. NUMBER OF CONCRETE RESURFACINGS BY THE TYPE AND UNDERLYING PAVEMENT

Underlying Pavement (a)

TYPE (a) JPCP JRCP CRCP AC/F OTHERS TOTALS

JPCP 220 44 25 175 12 476

JRCP 88 18 2 14 7 129

CRCP 22 26 2 17 - 67

FRC 10 2 4 14 2 32

PRC 2 - 1 1 - 4

TOTALS 342 90 34 221 21 708


TABLE 3. NUMBER OF CONCRETE RESURFACINGS BY TYPE AND INTERFACE

Interface (b)

TYPE (a) BONDED UNBONDED WHITETOPPING TOTAL

JPCP 105 218 151 474

JRCP 10 116 6 132

CRCP 3 50 13 66

FRC 8 16 8 32

PRC - 4 - 4

Totals 126 404 178 708


Location Rehabilitation Technique Project Size Cost/Lane km

North Carolina 1- 26 CPR 11.3 km $ 77,640

North Carolina 1-26 Crack/Seal and AC Overlay 4.2 km $ 232,920

Florida 1-10 CPR 106.2 km $ 38,820

Florida 1-10 Crack/Seal and 100 mm AC Overlay 51.5 km $117,190

Washington 1-90 CPR 53.1 km $73,800

Washington 1-90 110 mm AC Overlay 53.1 km $118,300

TABLE 4. COST COMPARISON OF PCC OVERLAYS V/S BITUMINOUS OVERLAYS (COST PER KM)



4. WHITETOPPING AS A CONCEPT

Whitetopping is an increasingly popular use of PCCresurfacing (overlay) as a rehabilitation or structuralstrengthening alternative on bituminous pavement. Allpavements including concrete pavements deteriorate withtime. The rate of deterioration is, however, different.Concrete pavement deteriorates slowly as compared tobituminous pavements. Fig. 3 presents the recommendedprocedures for preserving pavements againstdeterioration by application of PCC overlays. CPR isthe first response to a deteriorating concrete pavement.CPR relates to a non-overlay option and deals with thenumber of technique and procedures used to repairisolated area of distress. CPR is not discussed furtheras it is not the subject matter of the present Paper.

5. TYPE OF WHITETOPPING

From Fig. 3, it is seen that PCC overlay ofwhitetopping can be of two types, namely, unbonded typeand bonded type. Partially bonded types are alsomentioned in the literature. These are similar to un-bondedtype except that in such cases PCC overlays are laiddirectly on the existing bituminous pavement withoutmuch of surface preparation.

5.1. Un-bonded type

Thicker PCC overlays of un-bonded type commonlyknown as Conventional whitetopping can be used ondeteriorated bituminous pavements. This type ofwhitetopping is relevant for the rehabilitation orstrengthening of distressed/inadequate bituminouspavement on moderate to heavy trafficked corridors ofthe country. In India stage construction has been adoptedfor the bituminous pavements. All these pavements, whichhave now become badly due for strengthening, are thepotential candidates for Whitetopping. Conventional

Whitetopping is known to extend the life of bituminouspavement by 20 to 25 years. Technically they are similarto a newly laid concrete pavement except that bituminoussurface is the sub-base instead of Dry Lean Concrete(DLC) and no separation membrane or bond breakingfilm is provided.

5.2. Bonded Types

Ultra Thin Whitetopping is an example of bondedtype. In case of bonded type effect of composite actionis considered and thereby thin PCC overlays cater tosubstantial load of low to medium intensity. These areused at locations like intersections, round-abouts, parkinglots etc. Bonding of PCC overlay to the underlyingbituminous pavement surface by resorting to mechanicalprocess like milling achieves the monolithic behaviour ofthe two layers. It is, accordingly, a very economical andefficient means of enhancing the structural capacity ofthe bituminous pavement utilising the composite action.Inherent dis-advantage, however, is that if it is laid on abadly cracked surface the cracks will reappear. Millingremoves such cracks before bonding and is, therefore,mandatory.

Thin Whitetopping is in the middle of conventionaland Ultra-thin Whitetopping and accordingly can be usedon bituminous roads having light to moderate traffic.Milling though desirable is not mandatory. If required,bituminous overlay can be given in lieu of milling.

One of the pre-requisite for the construction of PCCoverlay is the uniform support condition of the PCCOverlay on the existing surface. In the absence ofuniform support condition, satisfactory performance ofany concrete pavement including overlay likeWhitetopping cannot take place. Most of the prematurePCC overlay failures are observed to be due to violationof this single requirement i.e. lack of uniform support.

Literature demarcates different types ofwhitetopping on the basis of degree of bonding andthickness of overlay. This is as below:-

Ultra Thin : Bonding mandatory, millingWhitetopping required, thickness upto 100 mm,

minimum thickness of the existingbituminous surface 75 mm (net aftermilling), with short joint spacing.Cannot be used on badly crackedbituminous surfaces. Substantialsurface preparation is involved.

Fig. 3. Overlay strategy of ageing pavements with level ofdeterioration

Source: American Concrete Pavement Association (ACPA)



Cost-efficient for intersections,check-posts, parking lots and lowvolume roads frequent with ruttingproblems due to stop/startconditions.

Thin : Bonding desirable, though notWhitetopping mandatory, milling desirable but thin

bituminous overlay of 25-50 mm inlieu of milling can be used, thicknessbetween 100 to 200 mm, with shortjoint spacing. Used for low tomoderate trafficked corridors.

Conventional : Similar to a new concreteWhitetopping pavement. Can be directly laid on

the existing bituminous pavementwithout much surface preparation.Thickness usually is equal to ormore than 200 mm. However, ThinWhitetopping and ConventionalWhitetopping do not have a veryrigid demarcation line and athickness between 150 mm to 250mm is quite common.

6. SCENARIOS CONSIDERED

Cost effectiveness of the whitetopping alternativein Indian context is proposed for analysis. For thispurpose three scenarios, typically representing the threetypes of bituminous road in the country, which could bethe potential candidates for whitetopping have beenconsidered. The three scenarios considered are asbelow:-

Scenario 1 Low Volume Road (C/W 7 m without

paved shoulders) Plain Terrain

Current traffic 300 CVPD.Projected design traffic*at 7.5% annual growthfor 10 yrs 2.3 MsaCharacteristic BBD**(assumed) 1.8 mmVDF as per IRC:81-1997(T-4) 1.5

Scenario II Medium Volume Road (C/W 7 m withoutpaved shoulders) Plain TerrainCurrent traffic 1000 CVPDProjected design

traffic at* 7.5%annual growthfor 15 yrs 33.36 MsaCharacteristic BBD**(assumed) 1.5 mmVDF as per IRC:81-1997(T-4) 3.5

Scenario III Heavy Volume Road (C/W 7 m withoutpaved shoulders, Plain Terrain)Current traffic 2000 CVPDProjected design trafficat 7.5%*annual growth for 20 yrs 142 MsaCharacteristic BBD**(assumed) 1.25 mmVDF as per IRC:81-1997(T-4) 4.5

* Projected traffic has been computed as per Para5.4.1of IRC:81-1997

** Benkelman Beam Deflections

7. COST COMPUTATION OF BITUMINOUSOVERLAY

7.1. Overlay Thickness Computation

Overlay Thicknesses have been computed for thethree scenarios as per IRC:81-1997. The overlaythickness of heavily traffic road with the projected trafficof 142 Msa has been computed by extrapolation. Thecomputed overlay thickness for the projected traffic ofthree scenarios is given in Table 5.

Scenario Computed Design lifeOverlay thickness of overlays

I 90 mm BM 10 years

II 150 mm BM 15 years

III 200 mm BM 20 years

BM = Bituminous Macadam

TABLE 5. COMPUTED OVERLAY THICKNESS

7.2. Basic rates used for analysis

The basic rates assumed are current (as per analysedtender rates). These are given in Table 6. The rates areapplicable and used for computation of the cost ofbituminous overlay as well as of Whitetopping.


TABLE 7. SCEDNARIO I: COST OF OVERLAY (90 mm BM)

Sl.No. Item of work (with computed Cost

quantity/cost) (Rs)

1. Tack Coat 7000 x 11.20 x 3 2.35 lakh

(Two coats of tack coat foraddl. crust and one coat for PR)

2. 90 mm BM (7000 x 0.09) 4480 28.22 lakh

3. 25 mm SDBC on BM (7000 x 8.82 lakh0.025) x 5040

4. Periodic Renewal (SDBC @ 8.82 lakh5 yrs) i.e. 5th yr (0.025 x 7000)x 5040 x 1

5. Routine Maintenance @ 5.00 lakhRs.50,000/- year/km 10 x 50,000

Total amount at current cost Rs.53.21 lakh Say 53 lakh

8. WHITETOPPING: GENERAL CONSIDERATIONS

8.1. Equivalent Whitetopping Treatment

The equivalent treatment of whitetoppingcorresponding to bituminous overlay for three scenarioshas been considered. The design of rigid pavement is ondifferent principles than those followed for design offlexible pavements. For rigid pavements each axle loadsare considered individually for the consumption of fatiguelife. This is against Equivalent Standard Axle Loads(ESAL) computed for flexible pavement by consideringall vehicles plying with a Vehicle Damage Factor (VDF).VDF takes care of higher loads than standard axle loadof 8.1 ton.

2. 150 mm BM addl. crust (7000 x 47.04 lakh0.150) 4480

3. 40 mm BC as surfacing (7000 x 0.004) 16.30 lakh5820

4. Add BC Periodic Renewal 40 mm 32.60 lakhcoat after 5th & 10th yrs 2(7000 x 0.04)x 5820

5. Add for Routine Maintenance @ 7.50 lakhRs.50000/yr for 15 yrs

Total amount at current cost 106.58 lakh Say 107 lakh

7.3. Cost of bituminous overlays

TABLE 6. BASIC (ITEM-WISE) RATES

S. No. Item of works Rate as on Oct.

2007(Rs)

1. Tack Coat 11.20/sqm

2. BM 4480/cum

3. DBM 4930/cum

4. SDBC 5040/cum

5. BC with CRMB 5820/cum

6. DLC 3490/cum

7. PQC 5330/cum

DBM = Dense Bituminous MacadamSD BC = Semi dense bituminous concreteB C = Bituminous concreteCRMB = Crumb rubber modified bitumenPQC = Paving quality concrete

TABLE 8. SCENARIO II: COST OF OVERLAY 150 mm BM


quantity/cost) (Rs)

1. Tack Coat 7000 x 11.20 x 4 3.14 lakh

(Two coats for addl. crust andtwo coats before Periodic renewalafter 5th &10th yrs)

TABLE 9. SCENARIO III: COST OF OVERLAY (200 mm)


quantity/cost) (Rs)

1. Tack coat 7000x11.20x4 3.14 lakh(2 operations for addl. Crustand 2 operations forPeriodic Renewal)

2. 100 mm BM (7000 x 0.1) 4480 31.36 lakh

3. 40 mm BC (7000 x 0.04) 5820 16.30 lakh

4. 40 mm BC Periodic Renewal 5th yr 16.30 lakh[(7000 x 0.04) x 5820]

5. 100 mm BM 10th yr (7000 x 0.1) x 4480 31.36lakh

40 mm BC (7000 x 0.04) 5820 16.30

40 mm BC Periodic Renewal 16.3015th yr (7000 x 0.04) 5820

Routine Maintenance @ 50000/- 10.00for 20 yrs

Total amount at current cost 141.06Say 41lakh



The equivalent whitetopping treatment has beenprescribed considering the following facts:-

• Characteristics deflection (BBD) of the existing

bituminous pavement has been kept as the limitingdeflection for rigid pavement design under themaximum axle load.

• ‘k’ value of sub-grade has been assumed as4.5 kg/cm3 corresponding to the CBR of 6 per centassumed for flexible pavement.

• The adequacy of the thickness of whitetopping hasbeen computed for maximum load likely to operateunder different scenario (some percentage of higheraxle loads and lower axle loads can, however,operate, as per the designs of rigid pavement).

• Design of whitetopping (PCC overlay) has beendone according to IRC:58-2002. Any specific changedue to smaller panel size etc. is duly explained in thedesign.

8.2. Design Assumptions

8.2.1. Ultra thin & thin whitetopping: The designof Thin Whitetopping and Ultra Thin Whitetopping areon different footing than Conventional Whitetopping.Both for Thin and Ultra Thin Whitetopping, panel sizesadopted are reduced. For the present analysis these havebeen kept as 1 m x 1 m. For such small panels chancesof two wheels (equivalent wheels) falling on the samepanel are remote. Accordingly, the Modulus of Rupture(MR) is computed from mid point loading rather thanthird point loading, as is the case, with the normal rigidpavement design. In case of conventional whitetopping,where panel spacing is about 4.5 m, the Modulus ofRupture (MR) is computed on the basis of third pointloading. Modulus of Rupture (MR) for small panel sizeas applicable to Ultra-thin Whitetopping/ThinWhitetopping is taken 1.5 times the value of MR forthird point loading. For details Appendix 1 may bereferred. Accordingly, MR adopted for Thin and Ultra-thin Whitetopping is 67.5 kg/cm2 for M-40 concreteinstead of 45 kg/cm2 which has been adopted forConventional Whitetopping.

Sub-base in case of Whitetopping is a bituminoussurface laid much before the PCC overlay(Whitetopping) is laid. Some useful life of such bituminoussub-base is, therefore, already consumed before PCC isoverlaid. To account for this, the fatigue life consumedfor all kinds of Whitetopping (including Conventional type)are taken as 0.75 or 75 per cent against 100 per cent

taken for the design of normal rigid pavement onsub-base (DLC) constructed together with PQC.

8.2.2. Conventional whitetopping: The panelsizes are large (4.5 m x 4.5 m typical) as is the case withnormal rigid pavements and hence no enhancement ofModulus of Rupture (MR) is done. The fatigue lifeconsumed, however, is taken as 75 per cent against 100per cent as above.

8.3. Equivalent Scenarios for Whitetopping

The equivalent of whitetopping for three scenariosof flexible overlays (Para 6) are as below:-

Scenario I: Ultra Thin Whitetopping

Current Traffic: 300 CVPDDesign Period: 10 yrsProjected Traffic: 225683(1.075)10 x 365 x 300:Design Traffic: 564200.25 x 225683 =Adopted 57500Thickness provided 100 mm

Scenario II: Thin WhitetoppingCurrent Traffic: 1000 CVPDDesign Period: 15 yrsProjected Traffic: 1079990(1.075)15 x 365 x 1000Design Traffic: 269997.60.25 x 1079990Adopted 270000Thickness provided 150 mm

Scenario III:Conventional 250 mmWhitetoppingCurrent Traffic: 2000 CVPDDesign Period: 20 yrsProjected Traffic: 3100931(1.075)20 x 365 x 2000:Design Traffic: 775232.800.25 x 3100931Adopted 775000Thickness provided 250 mm

9. DESIGN OF WHITETOPPING

9.1. Scenario I (Ultra Thin Whitetopping)100 mm

Thickness adequacy has also been checked forfatigue life for typically assumed axle load distributionvide Table 10 as per IRC 58-2002


TABLE 10. PCERCENTAGE OF AXLE LOAD FOR THE DESIGN OF UTWT (ASSUMED AXLE LOAD DISTRIBUTION)

Axle Load Percentage of axle Axle Load Percentage of axleClass, tons loads Class, tons loads

9-11 0.2 16-18 0.8

7-9 0.5 Less than 16 2.0

5-7 35.0 -

< 5 61.5 -

Total 97.2 Total 2.8

Single Axle Loads Tandem Axle Loads

Total Vehicles 57500

TABLE 11. DESIGN FROM FATIGUE CONSIDERATION USING PROGRAMME (IITRIGID)

Load in, tones Expected Repetition Load in, tones Expected Repetition

10 115 17 460

8 287 Less than 16 1150

6 20126

Less than 5 35362

Total 55890 Total 1610


SCENARIO I: ULTRA THIN WHITE TOPPING

Sl No. Pavement Layer Type and specification Ultra Thin White Topping(100 mm)

1 Traffic 300 CVPD

2 Thickness Designed 100 mm

3 Life 10 Years

4 Design Axles ( 25% of the projected) 57500

5 BBD (used as limiting Deflection) 1.8 mm

6 CBR 6%

7 Modulus of Subgrade Reaction 4.5 kg/cm3

8 Modified Modulus of Subgrade Reaction* 5.4 kg/cm3

9 Temperature Stresses (Delhi) 1.0 kg/cm2

10 Residual Stresses 66.5 kg/cm2

11 Edge Load stresses for 6 tones axle load 0.75x 46.29 34.71 kg/cm2

calculated from IITRIGID Prog

12 Stress ratio (for 6 tonees axle load) 34.71/67.5 = 0.51

13 Allowable repetition i.e. 0.75X485000 363750 which is > 57500, hence design issafe for individual axle load of 6 tones

* See Appendix II



TABLE 12. STRESS RATIO AT DIFFERENT AXLE LOADS UNDER THE CATEGORY OF SINGLE AXLES

Axle Load Stress Reduced Stress ratio* Expected Allowable Fatigue Life(AL) tones kg/ cm2 from Stress Col (3)/67.5 repetition Repetition Consumed

IIT RIGID kg/ cm2 fromcharts0.75 x Col (2)

(1) (2) (3) (4) (5) (6) (5)/(6)

10 69 52 0.77 115 274 0.42

8 58 44 0.65 287 7700 0.04

6 46 35 0.52 20126 326000 0.06

Less than 5 40 30 0.44 35362 unlimited 0

Total 55890 0.52

Total fatigue consumed = 0.52 (single axle) + 0.02 (tandem axle) = 0.54 < 0.75 hence design is safe

TABLE 13. STRESS RATIO AT DIFFERENT AXLE LOADS UNDER THE CATEGORY OF TANDEM AXLE.

Tandem Axle Stress kg/ Reduced Stress ratio Expected Fatigue life, Fatigue lifeLoad (AL) cm2 from Stress kg/ Col. 3/67.5 repetition N consumedtones charts cm2 Col

2 x 0.75

(1) (2) (3) (4) (5) (6) (7)

17 50.4 37.8 0.56 460 94100 0.01

Less than 16 48.2 36.0 0.53 1150 229000 0.01

- - Total 0.02

SCENARIO II : THIN WHITE TOPPING


1 Traffic 1000 CVPD


3 Life 15 Years

4 Design Axles ( 25% of the projected) 2,70,000


6 CBR 6%


8 Modified Modulus of Subgrade Reaction* 6.4 kg/cm3

9 Temperature Stresses (Delhi) 0.5 kg/cm2


11 Edge Load stresses for 9 tones axle load calculated from 34.3IITRIGID Prog

12 Stress ratio (for 9 tonees axle load) 34.3/67.5 = 0.51

13 Allowable Repetition i.e 0.75 x4.85 lacs 3.64 lacs (which is more than 2.7 lacs )Hencedesign is safe for 9 tones axle load

* See Appendix II


Thickness adequacy has also been checked for fatigue life for typically assumed axle load distribution vide Table15 as per IRC 58-2002

TABLE 15. DESIGN FROM FATIGUE CONSIDERATION USING PROGRAMME (IITRIGID)


12 5400 19 2160

10 13500 17 2700

8 40500 Less than 16 2700

6 94500

Less than 5 108540 -

Total 262440 Total -



Load (AL) Stress kg/cm2 Stress ratioCol Expected repetition Allowable Fatigue Lifetones from IIT RIGID (2)/67.5 Repetition Consumed

(1) (2) (3) (4) (5) (4)/(5)

12 43.5 0.64 5400 10200 0.53

10 37.46 0.55 13500 124000 0.11

8 31.15 0.46 40500 14335000 0.00

6 24.5 0.36 94500 unlimited 0.00

Less than 5 21.07 0.31 108540 unlimited 0.00

Total 262440 0.64

TABLE 14. PERCENTAGE OF AXLE LOAD FOR THE DESIGN OF TWT

Axle Load Percentage of axle Axle Load Percentage of axleClass, tons loads Class, tons load

11-13 2.0 18-20 0.8

9-11 5.0 16-18 1.0

7-9 15.0 Less than 16 1.0

5-7 35.0 -

< 5 40.2 -



Total Vehicles 270000



TABLE 17. STRESS RATIO AT DIFFERENT AXLE LOADS UNDER THE CATEGORY OF TANEM AXLE

Tandem Axle Stress kg/cm2 Stress ratio Expected Fatigue Fatigue lifeLoad (AL) tones from charts Col. 2/67.5 repetition life, N consumed

(1) (2) (3) (4) (5) (6)

19 28.62 0.42 2160 unlimited 0

17 26.23 0.38 2700 unlimited 0

Less than 16 - - 2700 unlimited 0

Total fatigue consumed = 0.64 (single axle) + 0.00 (tandem axle) = 0.64 < 0.75 hence design is safe. Further,maximum load stress 43.5 + temp stress i.e. 0.5 kg/cm2 = 44 kg/cm2 which is less than 67.5 kg/cm2

SCENARIO III: CONVENTIONAL WHITE TOPPING


1 Traffic 2000 CVPD


3 Life 20 Years

4 Design Axles ( 25% of the projected) 7.75 lacs


6 CBR 6%


8 Modified Modulus of Subgrade Reaction * 8.13 kg/cm3

9 Temperature Stresses (Delhi) 17.2 kg/cm2 when L = 4.5 m


11 Edge Load stresses for 13 tones axle load calculated from 21.2 kg/cm2

IITRIGID Prog

12 Stress ratio (for 13 tonees axle load) 45 = 0.47

13 Allowable Repetition i.e 0.75 x52 lakh 39 lakh (which is more than 7.75 lakh )Hencedesign is safe for each 13 tones axle loadindividually

Now, thickness can also be checked for fatigue for other axle load distribution (including 13 tones axle load) as perIRC 58-2002

Total Vehicles 7.75 lakh TABLE 18. PERCENTAGE OF AXLE LOADS FOR THE DESIGN OF CONVENTIONAL WHITETOPPING


15-17 3.75 28-30 0.2

13-15 12.5 26-28 0.2

11-13 10 24-26 0.2

9-11 15.0 22-24 0.4

7-9 20.0 20-22 0.4


* See Appendix II



Axle Load Stress kg/cm2 Stress ratio Expected Allowable Fatigue Life(AL) tones from IIT RIGID Col (2)/45 repetition Repetition Consumed

(1) (2) (3) (4) (5) (4)/(5)

16 25.3 0.56 29062 70575 0.41

14 22.5 0.50 96875 571500 0.17

12 19.7 0.44 77500 unlimited 0.00

10 - - 116250 unlimited 0.00

8 - - 155000 unlimited 0.00

6 - - 170500 unlimited 0.00

Less than 5 - - 108112 unlimited 0.00

Total - - 753300 Total 0.58

TABLE 19. DESIGN FROM FATIGUE CONSIDERATION USING PROGRFAMME (IITRIGID)



16 29062 29 1550

14 96875 27 1550

12 77500 25 1550

10 116250 23 3100

8 155000 21 3100

6 170500 19 3875

Less than 5 108113 17 3875

Total 753300 Less than 16 3100

Total 21700


5-7 22.0 18-20 0.5

<5 13.95 16-18 0.5

- - Less than 16 0.4


TABLE 21. STRESS RATIO AT DIFFERENT AXLE LOADS UNDER THE CATEGORY OF TANDEM AXLE

Tandem Axle Stress kg/cm2 Stress ratio Expected Fatigue life, Fatigue lifeLoad (AL) tones IIT RIGID Col. 2/45 repetition N consumed

(1) (2) (3) (4) (5) (6)

29 19.1 0.43 unlimited 1550 0.00

27 18.0 0.40 unlimited 1550 0.00



Since the residual stress = 27.8 kg/cm2 is more than the maximum stress i.e 25.3 kg/cm2 hence design is safe asper load distribution assumed.

Total fatigue consumed = 0.58 (single axle) + 0.00 (tandem axle) = 0.58 < 0.75 hence design is safe. Further,maximum load stress 25.3 + temp stress i.e. 17.2 kg/cm2 = 42.5 which is less than 45 kg/cm2. Hence design is safe.

10. COMPUTED COST OF WHITETOPPING

Tandem Axle Stress kg/cm2 Stress ratio Expected Fatigue life, Fatigue lifeLoad (AL) tones IIT RIGID Col. 2/45 repetition N consumed

25 - - 1550 0.00

23 - - - 3100 0.00

21 - - - 3100 0.00

19 - - - 3875 0.00

17 - - - 3875 0.00

Less than 16 - - - 3100 0.00

- - - 0.00

TABLE 22. COST OF ULTRA-THIN WHITETOPPING (100 mm)

Sl.No. Item Rate(Rs.) Quantity Sq.m Total Costin(Rs.Lakh)

1 Scarifying/ milling up to a depth of 40 mm, cleaning, 30/sqm 7000 2.10watering etc

2 Applying Tack coat as per MOSRTH Sps. 11.20/sq m 7000 0.78

3 Cost of PQC M 40 Grade concrete including, cost of 5330/ cu m 700 (mm) 37.31polymeric/polyolefin fibres, ~ 1kg/cum, form work,placing, laying a thickness of 100 mm, its compaction,finishing, curing, texturing, joint cutting in both directions(at an interval of 1m each upto a depth of 1/3rd of the slab’sthickness), use of three tie bars (10 mm dia deformed at aninterval 0f 30 cm c/c at butt types of joint in each panel ofsize 1mX1m, sealing of butt type joints.

4 Maintenance cost per annum (two lane 1 km) 25000 10 yrs 2.50

Total initial cost of UTWT in Rs , lakh for two lane 40.19

Total Life Cycle cost of UTWT, in Rs , lakh for two lane 42.69

10 cm thickness is safe up to an axle load of 6 tones for a maximum deflection of UTWT 0.125 cm for a traffic of 300 CVPDfor 10 years (considering allowable repetition 75 per cent of the specified)

Sl.No. Item Rate (Rs.) Quantity Sq.m Total Costin(Rs.Lakh)

1 Scarifying/ milling up to a depth of 40 mm, cleaning, 30/sqm 7000 2.10watering etc

2 Applying Tack coat as per MOSRTH Specifications. 11.20/sq m 7000 0.78

TABLE 23. COST OF THIN WHITETOPPING (150 mm)


15 cm thickness is safe for an axle load of 9 tones for 1000CVPD for 15 years. Higher loads may be allowedonly very limited


3 Cost of PQC M 40 Grade concrete including, cost of 5330/ cu m 1050 55.96polymeric/polyolefin fibres, 1kg/cum, form work, placing,laying a thickness of 150 mm, its compaction, finishing,curing, texturing, joint cutting in both directions at an intervalof 1m each upto a depth of 1/3rd of the slab’s thickness, use ofthree tie bars ( 10 mm dia deformed at an interval 0f 30 cm c/cat butt types of joint in each panel of size 1mX1m, sealing ofbutt type joints.

4 Cost of laying Bituminous macadam (75 mm thick) as profile 4480/ cum 525 23.52correction course

5 Maintenance cost per annum 25000 20 5.00

Total initial cost of TWT considering milling, in Rs , lakh for two lane 58.84

Total initial cost of TWT considering profile correction course, in Rs , lakh for two lane 80.26

Total Life cycle cost of TWT , in Rs , considering milling lakh for two lane 63.84

Total Life Cycle cost of TWT considering profile correction course, in Rs , lakh for two lane 85.26

TABLE 24. COST OF CONVENTIONAL WHITETOPPING (250 mm)

Conventional white topping 25 cm thickness is safe for an axle load of 13 tonne for 2000 CVPd for design trafficof 20 years but with some higher loads also as per distribution.


1 Cleaning, repair, and applying a white wash coat as 5.20/sq m 7000 0.36per MOSRTH Sps.

2 Cost of PQC M 40 Grade concrete including, cost of 5330/ cu m 1750 93.28polymeric/polyolefin fibres, 1kg/cum, form work,placing, laying a thickness of 200 mm, its compaction,finishing, curing, texturing, joint cutting in both directionsat an interval of 1m each upto a depth of 1/3rd of theslab’s thickness, use of three tie bars ( 10 mm diadeformed at an interval 0f 30 cm c/c at butt types ofjoint in each panel of size 1mX1m, sealing of butttype joints.

3 Maintenance cost per annum 25000 20 5.00

Total initial cost of conventional white topping, in Rs, lakh for two lane 93.64

Total Life Cycle cost of Conventional white topping, in Rs, lakh for two lane 98.64



Fig. 4. Histogram showing life cycle cost of Rigid andFlexible Overlays

11. ANALYSIS

From the perusal of the Table 25, the savings in theinitial cost of doing whitetopping against conventionalbituminous overlay is evidently convincing. Thecomparison is based on a relatively crude analysis doneon current cost basis without considering the likelyvariations in the future cost of bituminous materials andconcrete materials. Higher cost of white copping isconsidered because of lower thickness and more numberof joints than for conventional rigid pavement. This againgoes against the cost assumed for whitetopping, becauseas per the present trend the likely futuristic variations inthe cost of bitumen is expected to be more steep thanthose in concrete. The design of whitetopping particularlyin UTWT & TWT scenario is relatively quiteconservative in terms of the expected capabilities ofUTWT & TWT to carry heavier loads as compared tothe corresponding capabilities of bituminous overlays.This is because the design of bituminous overlays doesnot contemplate much higher loads than standard loads

TABLE 25. COMPARATIVE COST OF BITUMINOUS/WHITETOPPING OVERLAY (PER KM BASIS)

Scenario Bituminous Whitetopping Total cost of Total cost Saving in

Overlay thickness type & thickness bituminous of whitetopping Whitetoppingoverlay I/c I/c maintenance (Rs. Lakh)/

maintenance (Rs.)(Rs.) % Saving

I 90 mm BM 100 mm UTWT 53 lakh 42.69 lakh 10.31 lakh(19.04%)

II 150 mm BM 150 mm TWT 107 lakh 85.26 lakh 21.74 lakh(20.32%)

III 200 mm BM 200 mm 141 lakh 98.64 lakh 42.36Conventional lakh (30.04%)

due to low VDF assigned. This is particularly true forscenario I where VDF is considered 1.5.

The advantage of Thinner whitetoppings is quiteobvious in terms of cost savings due to small panel sizes.The advantage is apparently getting reduced significantlywhen the panel sizes are increased to 4.5 m x 4.5 mbeing typically adopted in case of concrete pavementsconstructed at present in the country. The temperaturestresses with large panel sizes become quite large toleave room to accommodate load stresses. The thicknessof such slabs is likely to be in the vicinity of 250 to 300mm. Tables 5 to 25 may be referred.

Concrete pavements have many advantages likeconservation of materials (due to less thickness), savingsin fuels, more environmental friendly, less to zeromaintenance, not very sensitive to temperature etc. Allthese advantages are also with whitetopping and are notrepeated for the sake of space. These have, however,not been considered in the evaluation of the cost-effectiveness in the analysis presented above. This willfuther add up.

The only disadvantage in whitetopping could be thatit requires longer period of curing and accordingly laneclosures during rehabilitation has to be longer. It is perhapsbecause of this limitation of concrete (compared to theease of bituminous pavement in this regard) that concretepavements did not find early applications in repair/rehabilitations. Fast track concrete pavement using EarlyTo Operate (EOT) Concrete is being used to overcomesuch shortcomings. The details of fast track constructionand EOT may be referred from some specialist literature.The advantages of concrete are obvious from the factthat research efforts have been made to device fast track


construction of concrete pavements, because despite thisone drawback, concrete is a better performing material,particularly in hot climate regions.

12. CONCLUSIONS

This Paper is a concept Paper. The objective wasto emphasize the cost-effectiveness of whitetopping asa rehabilitation measure of our bituminous pavementwhich are badly due for strengthening. The cost savingsshown on a kilometer basis suggests the likely impact,whitetopping will have in ensuring long performing betterroads at a much lesser cost. The only disadvantage islong lane closure and perhaps additional provision fordiversion of traffic during construction. Diversion oftraffic during construction, in any case, is a requirementalso for flexible pavement. This aspect is being neglectedand, therefore, it cannot be considered as an advantageof bituminous pavement. The authors recommend thatsome rehabilitation schemes be launched in the country

with whitetopping and the cost and performance aspectshould be watched. It is felt that whitetopping providesthe answer of rehabilitation of our pavements.

REFERENCES

1. NCHRP Synthesis 204, Transportation Research Board,1994

2. Concrete Overlays for Pavement Rehabilitation ACI325.13R-06, 2007

3. Whitetopping – State of the Practice, ACPA EB210.02P,1998

4. IRC:81-1997 “Guidelines for Strengthening of FlexiblePavements Using Benkelman Beam DeflectionTechnique”

5. IRC:58-2002 “Guidelines for the Design of Plain JointedRigid Pavements For Highways (Second Revision)”

6. IRC:15-2002 “Standard Specifications and Code ofPractice for Construction of Concrete Roads (ThirdRevision)”



Derivation Of the Formulae For Determiningmodulus of rupture Flexural Strength of ConcreteUnder Third Point loading (middle third loading)and central point loading (mid point loading)

Case I: Conventional White Topping (Mid thirdpoint loading)

Considering a case of concrete beam loaded attwo point as shown in Figure 1, for a contraction jointspacing of 4.5 m (maximum) with length /breadth ratioof 1.28.

Taking clockwise bending moment (BM) atpoint at point ‘A’:

BM = P/2x – /3 = P– /6

Now from the following principal equation i.e.:

M = f I y

F = (M y)/I

Where M = Bending moment (BM), kg cmI = Moment of Inertia of a beam, bd3/12,

cm4

F = Flexural strength/modulus of rupture atthird point loading (Figure 1),kg/cm2.

y = Distance of top/bottom fibre of thebeam from the neutral axis i.e d/2, cm

Therefore, F = (P– /6 d/2)/ bd3/12 = P– /bd2

Case 2: Ultra thin white Topping (UTWT) andThin white Topping (TWT)(Centre point loading)

Considering 2nd case, where, a concrete beam isloaded at central/middle point (small size panel/specimens/blocks) as shown in Figure 2, for a contractionjoint spacing of 1.25 m (maximum) with length /breadthratio of 1.2.

Taking clockwise bending moment (BM) at pointat point ‘A’:

BM = P/2x – /2 = P– /4

Now from the following principal equation i.e.:

M = f I y

F = (M y)/I

Where M = Bending moment (BM), kg cmI = Moment of Inertia of a beam, bd3/12,

cm4

F = Flexural strength/modulus of rupture atCentral/middle point loading(Figure 1) kg/cm2.

y = Distance of top/bottom fibre of thebeam from the neutral axis i.e d/2, cm

Therefore, F = (P– /4 d/2)/ bd3/12 = 3/2 P– /bd2

APPENDIX I


Appendix II

(Source: Corporation of Engineers and Portland Cement Association (PCA) USA.)1 pound persquare inch/inch = 0.027 kg/cm3.

Relation Between Benkelman Beam Deflection and modulus of Subgrade Reaction on the Top of Asphalt Pavement(Applicable for Conventional white topping, UTWT and TWT)

SINHA, KUMAR & JAIN ON

WHITETOPPING - A COST-EFFECTIVE REHABILITATION ALTERNATIVE FOR PRESERVING BITUMINOUS


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