WHITETOPPING - A COST-EFFECTIVE REHABILITATION ALTERNATIVE FOR PRESERVING BITUMINOUS PAVEMENTS ON LONG-TERM BASIS

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1 Paper No. 538 WHITETOPPING - A COST-EFFECTIVE REHABILITATION ALTERNATIVE 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 of Whitetopping. The brief literature review presents the cost-effectiveness of whitetopping as practiced in the developed world. The analysis with typical designs of different types of whitetopping has been presented in the Paper to acquaint the engineers at large about the design methods, which could be adopted in the country. The actual cost savings per kilometre wise in case of Ultra-thin & Thin Whitetopping are demonstrated. The Paper concludes based on analysis that Whitetopping with the thickness between 100 mm to 250 mm can be used in rehabilitating our large network of existing bituminous roads having low to moderate traffic. It is suggested that some pilot projects be done to further the emerging concept of whitetopping in the country. 1. INTRODUCTION The focus today is on the construction of long-term performing pavement, since pavements are the costliest component of Highways. Most of our roads have bituminous pavements with thin binder course. Only recently under NHDP bituminous pavements with thicker binder courses are being constructed. Bituminous pavements are showing early sign of distresses worldwide, due to increasing loads, intensity of traffic, high tyre pressure etc. The rutting, cracking and ageing etc are quite common. Reflective cracking is another form of distress in bituminous overlay. These distresses get more pronounced in hot climatic regions like India, since bitumen is highly sensitive to temperature. Performance of bituminous pavements in hot climatic regions is thus becoming somewhat doubtful. Concrete on the other hand is known to be a relatively stiffer material and is relatively less sensitive to high temperature. Accordingly, concrete pavements are being increasingly adopted as an alternative to traditional bituminous pavements. Even in terms of rehabilitation and repair the use of concrete is replacing traditional bituminous overlay because of better performance against rutting and cracking. This is the current international trend. Earlier, objection against the adoption of concrete pavement 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 these misconceptions are gradually vanishing. PCC overlays are being provided even on concrete pavements, similar to bituminous pavements. Repair of concrete pavement is also not that difficult now. Concrete pavements are known to have lasted in the developed world for about 40 to 50 years. Most of our bituminous pavements today, which are badly suffering from distresses like rutting, shoving, cracking etc are overdue for rehabilitation/strengthening. This will involve huge cost and consumption of scarce physical resources like aggregates and bitumen. Costeffectiveness of PCC overlays (whitetopping) vis-a-vis bituminous overlay, therefore, needs to be examined. Whitetopped roads on average have proved to be quite cost- effective besides giving an additional life of 20 to 30 years on average. The present Paper, which is a concept Paper, examines the concept of whitetopping as a cost-effective alternative to bituminous overlays. 2. REMEDY FOR DISTRESS IN BITUMINIOUS PAVEMENT BY WHITETOPPING Rutting is a common distress observed on bituminous pavements. It is a common experience that once rutting occurs on a bituminous pavement, placing a bituminous * Secretary General, IRC } secretarygen@irc.org.in **Scientist, CRRI New Delhi. } E- Mail: satander.crri@nic.in *** Chief Engineer (Retd.) Haryana PWD Written comments on this Paper are invited and will be received upto 31 st December, 2007

2 224 SINHA, KUMAR & JAIN ON overlay does not prevent its recurrence. Rutting reappears soon after the overlay. This is because bituminous overlay cannot be properly compacted in such wheel ruts and such overlays are not capable to stand up against today s high tyre pressure and traffic loads. On the contrary, concrete can uniformly fill such ruts and correct the surface profile. Concrete has much greater stiffness compared to bituminous overlay and, therefore, reflective cracking (quite common with bituminous overlays) are either eliminated or reduced substantially with concrete overlays. Bituminous mixes are sensitive to temperature. They are, therefore, quite amenable to plastic flow, which leads to distresses like transverse corrugation and localised bulging (shoving) caused by horizontal vehicle force. These distresses are quite common in case of bituminous overlays at the intersections, at round-abouts and at check-posts, due to frequent stop/start condition of heavy vehicles. They do not occur with concrete overlays. This is because concrete does not exhibit plastic flow. Concrete is less affected by seasonal weakening of the sub-grade since it distributes the load on a wider area through beam action. A study of test pavement at the AASHO Road Test (1962) has established that seasonal variations have much less effect on performance of concrete pavements than on bituminous pavements. Nearly 61 per cent of the bituminous test section failed during spring months compared with just 5.5 per cent of the concrete section in USA vide Fig.1. Some of the States in USA restrict the heavy loads during spring months vide Fig.2, even though enforcement is difficult. Concrete pavement is resilient throughout the entire year. Bituminous pavements/overlays are relatively more 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) during the spring season Source: ACPA EB210.02P 3. CURRENT TREND IN PCC OVERLAYS According to NCHRP synthesis 204 (1), in USA about 708 projects involving concrete resurfacing have been provided until Out of which, 189 projects are on existing bituminous pavement i.e. Whitetopping. Tables 1 to 3 give the trend in PCC overlays till 1993 in USA. TABLE1. NUMBER OF CONCRETE RESURFACING BY TYPE AND USE TYPE (a) Highways Streets Airfields TOTAL JPCP JRCP CRCP FCP PCP Totals Source: NCHRP Synthesis 204

3 WHITETOPPING - A COST-EFFECTIVE HIGHLIGHTS REHABILITATION OF THE 178 TH COUNCIL ALTERNATIVE MEETING FOR PRESERVING BITUMINOUS 225 PAVEMENTS ON LONG-TERM BASIS TABLE 2. NUMBER OF CONCRETE RESURFACINGS BY THE TYPE AND UNDERLYING PAVEMENT JPCP = Jointed Plain concrete Pavement JRCP =Jointed Reinforced Concrete Pavement CRCP = Continuously Reinforced Concrete Pavement FRC = Fiber Reinforced Concrete PRC = Prestressed Concrete AC/F = Asphalt Concrete (Bituminous) CPR = Concrete Pavement Restorations Underlying Pavement (a) TYPE (a) JPCP JRCP CRCP AC/F OTHERS TOTALS JPCP JRCP CRCP FRC PRC TOTALS Source: NCHRP Synthesis 204 TABLE 3. NUMBER OF CONCRETE RESURFACINGS BY TYPE AND INTERFACE Interface (b) TYPE (a) BONDED UNBONDED WHITETOPPING TOTAL JPCP JRCP CRCP FRC PRC Totals (a) Source: NCHRP Synthesis 204 In Indian context whitetopping has a larger role in future rehabilitation of the weak bituminous pavements. Advantage of whitetoping is its longer life compared to bituminous overlays, which is known to suffer early distress due to material related problems. Table 4 demonstrates low initial cost of PCC repair/rehabilitation compared to bituminous overlays as per the experience in USA. TABLE 4. COST COMPARISON OF PCC OVERLAYS V/S BITUMINOUS OVERLAYS (COST PER KM) 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 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 mm AC Overlay 53.1 km $118,300 Source: NCHRP Synthesis 204

4 226 SINHA, KUMAR & JAIN ON 4. WHITETOPPING AS A CONCEPT Whitetopping is an increasingly popular use of PCC resurfacing (overlay) as a rehabilitation or structural strengthening alternative on bituminous pavement. All pavements including concrete pavements deteriorate with time. The rate of deterioration is, however, different. Concrete pavement deteriorates slowly as compared to bituminous pavements. Fig. 3 presents the recommended procedures for preserving pavements against deterioration by application of PCC overlays. CPR is the first response to a deteriorating concrete pavement. CPR relates to a non-overlay option and deals with the number of technique and procedures used to repair isolated area of distress. CPR is not discussed further as it is not the subject matter of the present Paper. Fig. 3. Overlay strategy of ageing pavements with level of deterioration Source: American Concrete Pavement Association (ACPA) 5. TYPE OF WHITETOPPING From Fig. 3, it is seen that PCC overlay of whitetopping can be of two types, namely, unbonded type and bonded type. Partially bonded types are also mentioned in the literature. These are similar to un-bonded type except that in such cases PCC overlays are laid directly on the existing bituminous pavement without much of surface preparation Un-bonded type Thicker PCC overlays of un-bonded type commonly known as Conventional whitetopping can be used on deteriorated bituminous pavements. This type of whitetopping is relevant for the rehabilitation or strengthening of distressed/inadequate bituminous pavement on moderate to heavy trafficked corridors of the country. In India stage construction has been adopted for the bituminous pavements. All these pavements, which have now become badly due for strengthening, are the potential candidates for Whitetopping. Conventional Whitetopping is known to extend the life of bituminous pavement by 20 to 25 years. Technically they are similar to a newly laid concrete pavement except that bituminous surface is the sub-base instead of Dry Lean Concrete (DLC) and no separation membrane or bond breaking film is provided Bonded Types Ultra Thin Whitetopping is an example of bonded type. In case of bonded type effect of composite action is considered and thereby thin PCC overlays cater to substantial load of low to medium intensity. These are used at locations like intersections, round-abouts, parking lots etc. Bonding of PCC overlay to the underlying bituminous pavement surface by resorting to mechanical process like milling achieves the monolithic behaviour of the two layers. It is, accordingly, a very economical and efficient means of enhancing the structural capacity of the bituminous pavement utilising the composite action. Inherent dis-advantage, however, is that if it is laid on a badly cracked surface the cracks will reappear. Milling removes such cracks before bonding and is, therefore, mandatory. Thin Whitetopping is in the middle of conventional and Ultra-thin Whitetopping and accordingly can be used on 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 PCC overlay is the uniform support condition of the PCC Overlay on the existing surface. In the absence of uniform support condition, satisfactory performance of any concrete pavement including overlay like Whitetopping cannot take place. Most of the premature PCC overlay failures are observed to be due to violation of this single requirement i.e. lack of uniform support. Literature demarcates different types of whitetopping on the basis of degree of bonding and thickness of overlay. This is as below:- Ultra Thin Whitetopping : Bonding mandatory, milling required, thickness upto 100 mm, minimum thickness of the existing bituminous surface 75 mm (net after milling), with short joint spacing. Cannot be used on badly cracked bituminous surfaces. Substantial surface preparation is involved.

5 WHITETOPPING - A COST-EFFECTIVE HIGHLIGHTS REHABILITATION OF THE 178 TH COUNCIL ALTERNATIVE MEETING FOR PRESERVING BITUMINOUS 227 PAVEMENTS ON LONG-TERM BASIS Thin Whitetopping Conventional Whitetopping Cost-efficient for intersections, check-posts, parking lots and low volume roads frequent with rutting problems due to stop/start conditions. : Bonding desirable, though not mandatory, milling desirable but thin bituminous overlay of mm in lieu of milling can be used, thickness between 100 to 200 mm, with short joint spacing. Used for low to moderate trafficked corridors. : Similar to a new concrete pavement. Can be directly laid on the existing bituminous pavement without much surface preparation. Thickness usually is equal to or more than 200 mm. However, Thin Whitetopping and Conventional Whitetopping do not have a very rigid demarcation line and a thickness between 150 mm to 250 mm is quite common. 6. SCENARIOS CONSIDERED Cost effectiveness of the whitetopping alternative in Indian context is proposed for analysis. For this purpose three scenarios, typically representing the three types of bituminous road in the country, which could be the potential candidates for whitetopping have been considered. The three scenarios considered are as below:- 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 growth for 10 yrs 2.3 Msa Characteristic BBD** (assumed) 1.8 mm VDF as per IRC: (T-4) 1.5 Scenario II Medium Volume Road (C/W 7 m without paved shoulders) Plain Terrain Current traffic 1000 CVPD Projected design traffic at* 7.5% annual growth for 15 yrs Msa Characteristic BBD** (assumed) 1.5 mm VDF as per IRC: (T-4) 3.5 Scenario III Heavy Volume Road (C/W 7 m without paved shoulders, Plain Terrain) Current traffic 2000 CVPD Projected design traffic at 7.5%* annual growth for 20 yrs 142 Msa Characteristic BBD** (assumed) 1.25 mm VDF as per IRC: (T-4) 4.5 * Projected traffic has been computed as per Para 5.4.1of IRC: ** Benkelman Beam Deflections 7. COST COMPUTATION OF BITUMINOUS OVERLAY 7.1. Overlay Thickness Computation Overlay Thicknesses have been computed for the three scenarios as per IRC: The overlay thickness of heavily traffic road with the projected traffic of 142 Msa has been computed by extrapolation. The computed overlay thickness for the projected traffic of three scenarios is given in Table 5. TABLE 5. COMPUTED OVERLAY THICKNESS Scenario Computed Design life Overlay thickness of overlays I 90 mm BM 10 years II 150 mm BM 15 years III 200 mm BM 20 years BM = Bituminous Macadam 7.2. Basic rates used for analysis The basic rates assumed are current (as per analysed tender rates). These are given in Table 6. The rates are applicable and used for computation of the cost of bituminous overlay as well as of Whitetopping.

6 228 SINHA, KUMAR & JAIN ON 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 Macadam SD BC = Semi dense bituminous concrete B C = Bituminous concrete CRMB = Crumb rubber modified bitumen PQC = Paving quality concrete 7.3. Cost of bituminous overlays TABLE 7. SCEDNARIO I: COST OF OVERLAY (90 mm BM) Sl.No. Item of work (with computed quantity/cost) Cost (Rs) 1. Tack Coat 7000 x x lakh (Two coats of tack coat for addl. crust and one coat for PR) mm BM (7000 x 0.09) lakh mm SDBC on BM (7000 x 8.82 lakh 0.025) x Periodic Renewal 8.82 lakh 5 yrs) i.e. 5 th yr (0.025 x 7000) x 5040 x 1 5. Routine 5.00 lakh Rs.50,000/- year/km 10 x 50,000 Total amount at current cost Rs lakh Say 53 lakh TABLE 8. SCENARIO II: COST OF OVERLAY 150 mm BM Sl.No. Item of work (with computed quantity/cost) Cost (Rs) 1. Tack Coat 7000 x x lakh (Two coats for addl. crust and two coats before Periodic renewal after 5 th &10 th yrs) mm BM addl. crust (7000 x lakh 0.150) mm BC as surfacing (7000 x 0.004) lakh Add BC Periodic Renewal 40 mm lakh coat after 5 th & 10 th yrs 2(7000 x 0.04) x Add for Routine 7.50 lakh Rs.50000/yr for 15 yrs Total amount at current cost lakh Say 107 lakh TABLE 9. SCENARIO III: COST OF OVERLAY (200 mm) Sl.No. Item of work (with computed Cost quantity/cost) (Rs) 1. Tack coat 7000x11.20x lakh (2 operations for addl. Crust and 2 operations for Periodic Renewal) mm BM (7000 x 0.1) lakh mm BC (7000 x 0.04) lakh mm BC Periodic Renewal 5 th yr lakh [(7000 x 0.04) x 5820] mm BM 10 th yr (7000 x 0.1) x lakh 40 mm BC (7000 x 0.04) mm BC Periodic Renewal th yr (7000 x 0.04) 5820 Routine 50000/ for 20 yrs Total amount at current cost Say 41lakh 8. WHITETOPPING: GENERAL CONSIDERATIONS 8.1. Equivalent Whitetopping Treatment The equivalent treatment of whitetopping corresponding to bituminous overlay for three scenarios has been considered. The design of rigid pavement is on different principles than those followed for design of flexible pavements. For rigid pavements each axle loads are considered individually for the consumption of fatigue life. This is against Equivalent Standard Axle Loads (ESAL) computed for flexible pavement by considering all vehicles plying with a Vehicle Damage Factor (VDF). VDF takes care of higher loads than standard axle load of 8.1 ton.

7 WHITETOPPING - A COST-EFFECTIVE HIGHLIGHTS REHABILITATION OF THE 178 TH COUNCIL ALTERNATIVE MEETING FOR PRESERVING BITUMINOUS 229 PAVEMENTS ON LONG-TERM BASIS The equivalent whitetopping treatment has been prescribed considering the following facts:- Characteristics deflection (BBD) of the existing bituminous pavement has been kept as the limiting deflection for rigid pavement design under the maximum axle load. k value of sub-grade has been assumed as 4.5 kg/cm 3 corresponding to the CBR of 6 per cent assumed for flexible pavement. The adequacy of the thickness of whitetopping has been computed for maximum load likely to operate under different scenario (some percentage of higher axle loads and lower axle loads can, however, operate, as per the designs of rigid pavement). Design of whitetopping (PCC overlay) has been done according to IRC: Any specific change due to smaller panel size etc. is duly explained in the design Design Assumptions Ultra thin & thin whitetopping: The design of Thin Whitetopping and Ultra Thin Whitetopping are on different footing than Conventional Whitetopping. Both for Thin and Ultra Thin Whitetopping, panel sizes adopted are reduced. For the present analysis these have been kept as 1 m x 1 m. For such small panels chances of two wheels (equivalent wheels) falling on the same panel are remote. Accordingly, the Modulus of Rupture (MR) is computed from mid point loading rather than third point loading, as is the case, with the normal rigid pavement design. In case of conventional whitetopping, where panel spacing is about 4.5 m, the Modulus of Rupture (MR) is computed on the basis of third point loading. Modulus of Rupture (MR) for small panel size as applicable to Ultra-thin Whitetopping/Thin Whitetopping is taken 1.5 times the value of MR for third point loading. For details Appendix 1 may be referred. Accordingly, MR adopted for Thin and Ultrathin Whitetopping is 67.5 kg/cm 2 for M-40 concrete instead of 45 kg/cm 2 which has been adopted for Conventional Whitetopping. Sub-base in case of Whitetopping is a bituminous surface laid much before the PCC overlay (Whitetopping) is laid. Some useful life of such bituminous sub-base is, therefore, already consumed before PCC is overlaid. To account for this, the fatigue life consumed for 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 on sub-base (DLC) constructed together with PQC Conventional whitetopping: The panel sizes are large (4.5 m x 4.5 m typical) as is the case with normal rigid pavements and hence no enhancement of Modulus of Rupture (MR) is done. The fatigue life consumed, however, is taken as 75 per cent against 100 per cent as above Equivalent Scenarios for Whitetopping The equivalent of whitetopping for three scenarios of flexible overlays (Para 6) are as below:- Scenario I: Ultra Thin Whitetopping Current Traffic: 300 CVPD Design Period: 10 yrs Projected Traffic: (1.075) 10 x 365 x 300: Design Traffic: x = Adopted Thickness provided 100 mm Scenario II: Thin Whitetopping Current Traffic: Design Period: 1000 CVPD 15 yrs Projected Traffic: (1.075) 15 x 365 x 1000 Design Traffic: x Adopted Thickness provided 150 mm Scenario III:Conventional Whitetopping Current Traffic: Design Period: 250 mm 2000 CVPD 20 yrs Projected Traffic: (1.075) 20 x 365 x 2000: Design Traffic: x Adopted Thickness provided 250 mm 9. DESIGN OF WHITETOPPING 9.1. Scenario I (Ultra Thin Whitetopping) 100 mm Thickness adequacy has also been checked for fatigue life for typically assumed axle load distribution vide Table 10 as per IRC

8 230 SINHA, KUMAR & JAIN ON TABLE 10. PCERCENTAGE OF AXLE LOAD FOR THE DESIGN OF UTWT (ASSUMED AXLE LOAD DISTRIBUTION) Total Vehicles Single Axle Loads 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) BBD (used as limiting Deflection) 1.8 mm 6 CBR 6% 7 Modulus of Subgrade Reaction 4.5 kg/cm 3 8 Modified Modulus of Subgrade Reaction* 5.4 kg/cm 3 9 Temperature Stresses (Delhi) 1.0 kg/cm 2 10 Residual Stresses 66.5 kg/cm 2 11 Edge Load stresses for 6 tones axle load 0.75x kg/cm 2 calculated from IITRIGID Prog 12 Stress ratio (for 6 tonees axle load) 34.71/67.5 = Allowable repetition i.e. 0.75X which is > 57500, hence design is safe for individual axle load of 6 tones * See Appendix II Tandem Axle Loads Axle Load Percentage of axle Axle Load Percentage of axle Class, tons loads Class, tons loads Less than < Total 97.2 Total 2.8 TABLE 11. DESIGN FROM FATIGUE CONSIDERATION USING PROGRAMME (IITRIGID) Single Axle Loads Tandem Axle Loads Load in, tones Expected Repetition Load in, tones Expected Repetition Less than Less than Total Total 1610

9 WHITETOPPING - A COST-EFFECTIVE HIGHLIGHTS REHABILITATION OF THE 178 TH COUNCIL ALTERNATIVE MEETING FOR PRESERVING BITUMINOUS 231 PAVEMENTS ON LONG-TERM BASIS 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/ cm 2 from Stress Col (3)/67.5 repetition Repetition Consumed IIT RIGID kg/ cm 2 from charts 0.75 x Col (2) (1) (2) (3) (4) (5) (6) (5)/(6) Less than unlimited 0 Total 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 life Load (AL) cm 2 from Stress kg/ Col. 3/67.5 repetition N consumed tones charts cm 2 Col 2 x 0.75 (1) (2) (3) (4) (5) (6) (7) Less than Total 0.02 Total fatigue consumed = 0.52 (single axle) (tandem axle) = 0.54 < 0.75 hence design is safe SCENARIO II : THIN WHITE TOPPING Sl No. Pavement Layer Type and specification Ultra Thin White Topping(150 mm) 1 Traffic 1000 CVPD 2 Thickness Designed 150 mm 3 Life 15 Years 4 Design Axles ( 25% of the projected) 2,70,000 5 BBD (used as limiting Deflection) 1.5 mm 6 CBR 6% 7 Modulus of Subgrade Reaction 4.5 kg/cm 3 8 Modified Modulus of Subgrade Reaction* 6.4 kg/cm 3 9 Temperature Stresses (Delhi) 0.5 kg/cm 2 10 Residual Stresses 67.0 kg/cm 2 11 Edge Load stresses for 9 tones axle load calculated from 34.3 IITRIGID Prog 12 Stress ratio (for 9 tonees axle load) 34.3/67.5 = Allowable Repetition i.e 0.75 x4.85 lacs 3.64 lacs (which is more than 2.7 lacs )Hence design is safe for 9 tones axle load * See Appendix II

10 232 SINHA, KUMAR & JAIN ON Thickness adequacy has also been checked for fatigue life for typically assumed axle load distribution vide Table 15 as per IRC Total Vehicles Single Axle Loads TABLE 14. PERCENTAGE OF AXLE LOAD FOR THE DESIGN OF TWT Tandem Axle Loads Axle Load Percentage of axle Axle Load Percentage of axle Class, tons loads Class, tons load Less than < Total 97.2 Total 2.8 TABLE 15. DESIGN FROM FATIGUE CONSIDERATION USING PROGRAMME (IITRIGID) Single Axle Loads Tandem Axle Loads Load in, tones Expected Repetition Load in, tones Expected Repetition Less than Less than Total Total - TABLE 16. STRESS RATIO AT DIFFERENT AXLE LOADS UNDER THE CATEGORY OF SINGLE AXLES Load (AL) Stress kg/cm 2 Stress ratiocol Expected repetition Allowable Fatigue Life tones from IIT RIGID (2)/67.5 Repetition Consumed (1) (2) (3) (4) (5) (4)/(5) unlimited 0.00 Less than unlimited 0.00 Total

11 WHITETOPPING - A COST-EFFECTIVE HIGHLIGHTS REHABILITATION OF THE 178 TH COUNCIL ALTERNATIVE MEETING FOR PRESERVING BITUMINOUS 233 PAVEMENTS ON LONG-TERM BASIS TABLE 17. STRESS RATIO AT DIFFERENT AXLE LOADS UNDER THE CATEGORY OF TANEM AXLE Tandem Axle Stress kg/cm 2 Stress ratio Expected Fatigue Fatigue life Load (AL) tones from charts Col. 2/67.5 repetition life, N consumed (1) (2) (3) (4) (5) (6) unlimited unlimited 0 Less than unlimited 0 Total fatigue consumed = 0.64 (single axle) (tandem axle) = 0.64 < 0.75 hence design is safe. Further, maximum load stress temp stress i.e. 0.5 kg/cm 2 = 44 kg/cm 2 which is less than 67.5 kg/cm 2 SCENARIO III: CONVENTIONAL WHITE TOPPING Sl No. Pavement Layer Type and specification Ultra Thin White Topping(150 mm) 1 Traffic 2000 CVPD 2 Thickness Designed 250 mm 3 Life 20 Years 4 Design Axles ( 25% of the projected) 7.75 lacs 5 BBD (used as limiting Deflection) 1.2 mm 6 CBR 6% 7 Modulus of Subgrade Reaction 4.5 kg/cm 3 8 Modified Modulus of Subgrade Reaction * 8.13 kg/cm 3 9 Temperature Stresses (Delhi) 17.2 kg/cm 2 when L = 4.5 m 10 Residual Stresses 27.8 kg/cm 2 11 Edge Load stresses for 13 tones axle load calculated from 21.2 kg/cm 2 IITRIGID Prog 12 Stress ratio (for 13 tonees axle load) 45 = Allowable Repetition i.e 0.75 x52 lakh 39 lakh (which is more than 7.75 lakh )Hence design is safe for each 13 tones axle load individually * See Appendix II Now, thickness can also be checked for fatigue for other axle load distribution (including 13 tones axle load) as per IRC TABLE 18. PERCENTAGE OF AXLE LOADS FOR THE DESIGN OF CONVENTIONAL WHITETOPPING Total Vehicles 7.75 lakh Single Axle Loads Tandem Axle Loads Axle Load Percentage of axle Axle Load Percentage of axle Class, tons loads Class, tons load

12 234 SINHA, KUMAR & JAIN ON Axle Load Percentage of axle Axle Load Percentage of axle Class, tons loads Class, tons load < Less than Total 97.2 Total 2.8 TABLE 19. DESIGN FROM FATIGUE CONSIDERATION USING PROGRFAMME (IITRIGID) Single Axle Loads Tandem Axle Loads Load in, tones Expected Repetition Load in, tones Expected Repetition Less than Total Less than Total TABLE 20. STRESS RATIO AT DIFFERENT AXLE LOADS UNDER THE CATEGORY OF SINGLE AXLES Axle Load Stress kg/cm 2 Stress ratio Expected Allowable Fatigue Life (AL) tones from IIT RIGID Col (2)/45 repetition Repetition Consumed (1) (2) (3) (4) (5) (4)/(5) unlimited unlimited unlimited unlimited 0.00 Less than unlimited 0.00 Total Total 0.58 TABLE 21. STRESS RATIO AT DIFFERENT AXLE LOADS UNDER THE CATEGORY OF TANDEM AXLE Tandem Axle Stress kg/cm 2 Stress ratio Expected Fatigue life, Fatigue life Load (AL) tones IIT RIGID Col. 2/45 repetition N consumed (1) (2) (3) (4) (5) (6) unlimited unlimited

13 WHITETOPPING - A COST-EFFECTIVE HIGHLIGHTS REHABILITATION OF THE 178 TH COUNCIL ALTERNATIVE MEETING FOR PRESERVING BITUMINOUS 235 PAVEMENTS ON LONG-TERM BASIS Tandem Axle Stress kg/cm 2 Stress ratio Expected Fatigue life, Fatigue life Load (AL) tones IIT RIGID Col. 2/45 repetition N consumed Less than Since the residual stress = 27.8 kg/cm 2 is more than the maximum stress i.e 25.3 kg/cm 2 per load distribution assumed. hence design is safe as Total fatigue consumed = 0.58 (single axle) (tandem axle) = 0.58 < 0.75 hence design is safe. Further, maximum load stress temp stress i.e kg/cm 2 = 42.5 which is less than 45 kg/cm 2. Hence design is safe. 10. COMPUTED COST OF WHITETOPPING TABLE 22. COST OF ULTRA-THIN WHITETOPPING (100 mm) Sl.No. Item Rate(Rs.) Quantity Sq.m Total Cost in(rs. Lakh) 1 Scarifying/ milling up to a depth of 40 mm, cleaning, 30/sqm watering etc 2 Applying Tack coat as per MOSRTH Sps /sq m Cost of PQC M 40 Grade concrete including, cost of 5330/ cu m 700 (mm) polymeric/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 1/3 rd of the slab s thickness), use of three tie bars (10 mm dia deformed at an interval 0f 30 cm c/c at butt types of joint in each panel of size 1mX1m, sealing of butt type joints. 4 Maintenance cost per annum (two lane 1 km) yrs 2.50 Total initial cost of UTWT in Rs, lakh for two lane Total Life Cycle cost of UTWT, in Rs, lakh for two lane cm thickness is safe up to an axle load of 6 tones for a maximum deflection of UTWT cm for a traffic of 300 CVPD for 10 years (considering allowable repetition 75 per cent of the specified) TABLE 23. COST OF THIN WHITETOPPING (150 mm) Sl.No. Item Rate (Rs.) Quantity Sq.m Total Cost in(rs. Lakh) 1 Scarifying/ milling up to a depth of 40 mm, cleaning, 30/sqm watering etc 2 Applying Tack coat as per MOSRTH Specifications /sq m

14 236 SINHA, KUMAR & JAIN ON Sl.No. Item Rate(Rs.) Quantity Sq.m Total Cost in(rs. Lakh) 3 Cost of PQC M 40 Grade concrete including, cost of 5330/ cu m polymeric/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 interval of 1m each upto a depth of 1/3 rd of the slab s thickness, use of three tie bars ( 10 mm dia deformed at an interval 0f 30 cm c/c at butt types of joint in each panel of size 1mX1m, sealing of butt type joints. 4 Cost of laying Bituminous macadam (75 mm thick) as profile 4480/ cum correction course 5 Maintenance cost per annum Total initial cost of TWT considering milling, in Rs, lakh for two lane Total initial cost of TWT considering profile correction course, in Rs, lakh for two lane Total Life cycle cost of TWT, in Rs, considering milling lakh for two lane Total Life Cycle cost of TWT considering profile correction course, in Rs, lakh for two lane cm thickness is safe for an axle load of 9 tones for 1000CVPD for 15 years. Higher loads may be allowed only very limited TABLE 24. COST OF CONVENTIONAL WHITETOPPING (250 mm) Sl.No. Item Rate(Rs.) Quantity Sq.m Total Cost in(rs. Lakh) 1 Cleaning, repair, and applying a white wash coat as 5.20/sq m per MOSRTH Sps. 2 Cost of PQC M 40 Grade concrete including, cost of 5330/ cu m polymeric/polyolefin fibres, 1kg/cum, form work, placing, laying a thickness of 200 mm, its compaction, finishing, curing, texturing, joint cutting in both directions at an interval of 1m each upto a depth of 1/3 rd of the slab s thickness, use of three tie bars ( 10 mm dia deformed at an interval 0f 30 cm c/c at butt types of joint in each panel of size 1mX1m, sealing of butt type joints. 3 Maintenance cost per annum Total initial cost of conventional white topping, in Rs, lakh for two lane Total Life Cycle cost of Conventional white topping, in Rs, lakh for two lane Conventional white topping 25 cm thickness is safe for an axle load of 13 tonne for 2000 CVPd for design traffic of 20 years but with some higher loads also as per distribution.

15 WHITETOPPING - A COST-EFFECTIVE HIGHLIGHTS REHABILITATION OF THE 178 TH COUNCIL ALTERNATIVE MEETING FOR PRESERVING BITUMINOUS 237 PAVEMENTS ON LONG-TERM BASIS 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 Whitetopping overlay I/c I/c maintenance (Rs. Lakh)/ maintenance (Rs.) (Rs.) % Saving I 90 mm BM 100 mm UTWT 53 lakh lakh lakh(19.04%) II 150 mm BM 150 mm TWT 107 lakh lakh lakh(20.32%) III 200 mm BM 200 mm 141 lakh lakh Conventional lakh (30.04%) Fig. 4. Histogram showing life cycle cost of Rigid and Flexible Overlays 11. ANALYSIS From the perusal of the Table 25, the savings in the initial cost of doing whitetopping against conventional bituminous overlay is evidently convincing. The comparison is based on a relatively crude analysis done on current cost basis without considering the likely variations in the future cost of bituminous materials and concrete materials. Higher cost of white copping is considered because of lower thickness and more number of joints than for conventional rigid pavement. This again goes against the cost assumed for whitetopping, because as per the present trend the likely futuristic variations in the cost of bitumen is expected to be more steep than those in concrete. The design of whitetopping particularly in UTWT & TWT scenario is relatively quite conservative in terms of the expected capabilities of UTWT & TWT to carry heavier loads as compared to the corresponding capabilities of bituminous overlays. This is because the design of bituminous overlays does not contemplate much higher loads than standard loads due to low VDF assigned. This is particularly true for scenario I where VDF is considered 1.5. The advantage of Thinner whitetoppings is quite obvious in terms of cost savings due to small panel sizes. The advantage is apparently getting reduced significantly when the panel sizes are increased to 4.5 m x 4.5 m being typically adopted in case of concrete pavements constructed at present in the country. The temperature stresses with large panel sizes become quite large to leave room to accommodate load stresses. The thickness of such slabs is likely to be in the vicinity of 250 to 300 mm. Tables 5 to 25 may be referred. Concrete pavements have many advantages like conservation of materials (due to less thickness), savings in fuels, more environmental friendly, less to zero maintenance, not very sensitive to temperature etc. All these advantages are also with whitetopping and are not repeated for the sake of space. These have, however, not been considered in the evaluation of the costeffectiveness in the analysis presented above. This will futher add up. The only disadvantage in whitetopping could be that it requires longer period of curing and accordingly lane closures during rehabilitation has to be longer. It is perhaps because of this limitation of concrete (compared to the ease of bituminous pavement in this regard) that concrete pavements did not find early applications in repair/ rehabilitations. Fast track concrete pavement using Early To Operate (EOT) Concrete is being used to overcome such shortcomings. The details of fast track construction and EOT may be referred from some specialist literature. The advantages of concrete are obvious from the fact that research efforts have been made to device fast track

16 238 SINHA, KUMAR & JAIN ON construction of concrete pavements, because despite this one drawback, concrete is a better performing material, particularly in hot climate regions. 12. CONCLUSIONS This Paper is a concept Paper. The objective was to emphasize the cost-effectiveness of whitetopping as a rehabilitation measure of our bituminous pavement which are badly due for strengthening. The cost savings shown on a kilometer basis suggests the likely impact, whitetopping will have in ensuring long performing better roads at a much lesser cost. The only disadvantage is long lane closure and perhaps additional provision for diversion of traffic during construction. Diversion of traffic during construction, in any case, is a requirement also for flexible pavement. This aspect is being neglected and, therefore, it cannot be considered as an advantage of bituminous pavement. The authors recommend that some rehabilitation schemes be launched in the country with whitetopping and the cost and performance aspect should be watched. It is felt that whitetopping provides the answer of rehabilitation of our pavements. REFERENCES 1. NCHRP Synthesis 204, Transportation Research Board, Concrete Overlays for Pavement Rehabilitation ACI R-06, Whitetopping State of the Practice, ACPA EB210.02P, IRC: Guidelines for Strengthening of Flexible Pavements Using Benkelman Beam Deflection Technique 5. IRC: Guidelines for the Design of Plain Jointed Rigid Pavements For Highways (Second Revision) 6. IRC: Standard Specifications and Code of Practice for Construction of Concrete Roads (Third Revision)

17 WHITETOPPING - A COST-EFFECTIVE HIGHLIGHTS REHABILITATION OF THE 178 TH COUNCIL ALTERNATIVE MEETING FOR PRESERVING BITUMINOUS 239 PAVEMENTS ON LONG-TERM BASIS APPENDIX I Derivation Of the Formulae For Determining modulus of rupture Flexural Strength of Concrete Under Third Point loading (middle third loading) and central point loading (mid point loading) Case I: Conventional White Topping (Mid third point loading) Considering a case of concrete beam loaded at two point as shown in Figure 1, for a contraction joint spacing of 4.5 m (maximum) with length /breadth ratio of Case 2: Ultra thin white Topping (UTWT) and Thin white Topping (TWT) (Centre point loading) Considering 2nd case, where, a concrete beam is loaded at central/middle point (small size panel/ specimens/blocks) as shown in Figure 2, for a contraction joint spacing of 1.25 m (maximum) with length /breadth ratio of 1.2. Taking clockwise bending moment (BM) at point 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 cm I = Moment of Inertia of a beam, bd 3 /12, cm 4 F = Flexural strength/modulus of rupture at third point loading (Figure 1), kg/cm 2. y = Distance of top/bottom fibre of the beam from the neutral axis i.e d/2, cm Therefore, F = (P /6 d/2)/ bd 3 /12 = P /bd 2 Taking clockwise bending moment (BM) at point at 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 cm I = Moment of Inertia of a beam, bd 3 /12, cm 4 F = Flexural strength/modulus of rupture at Central/middle point loading (Figure 1) kg/cm 2. y = Distance of top/bottom fibre of the beam from the neutral axis i.e d/2, cm Therefore, F = (P /4 d/2)/ bd 3 /12 = 3/2 P /bd 2

18 240 SINHA, KUMAR & JAIN ON WHITETOPPING - A COST-EFFECTIVE REHABILITATION ALTERNATIVE FOR PRESERVING BITUMINOUS PAVEMENTS ON LONG-TERM BASIS Appendix II (Source: Corporation of Engineers and Portland Cement Association (PCA) USA.) 1 pound persquare inch/inch = kg/cm 3. Relation Between Benkelman Beam Deflection and modulus of Subgrade Reaction on the Top of Asphalt Pavement (Applicable for Conventional white topping, UTWT and TWT)