Featutes of New Guideline for the Design of Flexible Pavement.pptx

flexible pavement

1. Features of New Guidelines for the Design of Flexible Pavement- IRC:37-2012 Training Resource Person NAWRAJ BHATTA 28th November 2013

2. Presentation Outline - Introduction - Salient Features of New Guideline - Example Illustrating Design Methods - Introduction to Perpetual Pavement

3. Introduction 1 st published in 1970 – Based on CBR & No. of CV upto 1500 per day 1 st Revision in 1984 – empirical design charts available upto 30 MSA 2 nd Revision in 2001- design charts available upto 150 MSA; Semi-mechanistic approach, fatigue & rut criteria based on MORTH Research Scheme R-56, F-Pave introduced 3 rd Revision in 2012 History of IRC:37

4. Salient Features of New Guideline Concept of Effective Subgrade CBR; Min m CBR is 8 % for roads having CV traffic exceeding 450 vehicles per day Reference Axle Load for Single Axle Single Tyre (SAST) and Tridem Axle Dual Tyre (TRDT) Categories LDF for 2-lane single CWY road changed to 50 % of 2-directional traffic (corresponding value in earlier version was 75 %) Design for Higher Reliability Provision of Rut Resistant Surface Layer – Avoid Top Down Cracking Use of Fatigue Resistant Bottom Layer

5. Salient Features of New Guideline Reclaimed Asphalt Layers (RAP) Stabilized Sub base and Base Layers w/ SAMI GSB to be in 2 Layers, Both Layers to be designed Use of IITPAVE for Structural Analysis Perpetual Pavement

6. Concept of Effective Subgrade CBR Three situations emerge : CBR of embankment / foundation material considerably less than CBR of select sub-grade CBR of embankment / foundation material considerably higher than CBR of select sub-grade CBR of embankment / foundation material is more or less equals to CBR of select sub-grade For situation 2 - CBR of select sub-grade may be adopted for design. For situation 3 – Design method is same as previous guideline For situation 1 – Effective CBR must be determined and adopted in the design

7. Concept of Effective CBR CBR of Compacted Borrow Material – 500 mm Figure above shows that if the CBR of the 500 mm thick compacted sub-grade is not significantly higher than that of the embankment below it, then effective CBR of the sub-grade is almost equals to the CBR of compacted sub-grade

8. Reference Axle Load for Single Axle Single Tyre (SAST) and Tridem Axle Dual Tyre (TRADT) Axle Group Single axle single tyre (SAST) Single axle dual tyre (SADT) Tandem axle dual tyre (TADT) Tridem axle dual tyre (TRADT) Reference axle load, (kN) 65 80 148 224 New Guideline provides reference axle loads for SAST and TRADT category which enabled equivalency factor for these types of axles to be considered in the design

9. Sample Size for Axle Load Survey & LDF Total no. of commercial vehicles /day Minimum % of commercial traffic to be surveyed <3000 20 % 3000-6000 15 % >6000 10% Source: Clause 4.4.4 of IRC:37-2012 Type of facility Lane distribution factor, LDF 2- lane single carriageway 50 % of total two directional traffic 4- lane single carriageway 40 % of total two directional traffic 4- lane divided carriageway 75 % of total one directional traffic 6-lane divided carriageway 60 % of total one directional traffic

10. Design for Higher Reliability In Earlier version of the Guide, Formulae for Fatigue & Rut damage were available for 80 % reliability for all traffic. Similarly, design catalogues were also available for 80 % reliability only New Guideline recommends 90 % reliability to be applied to fatigue and rut for traffic exceeding 30 msa ; and 80 % reliability is restricted for traffic upto 30 msa only. The corresponding equations are Criteria R = 80 % R=90% Fatigue Rut

11. Fatigue Criteria for Cementitious Layers Two models are suggested as under: Australian model MEPDG model Criteria / Level Fatigue Life Applicable to Australian Model (Level 1) Applicable to all traffic scenarios; RF =2 for roads carrying < 1500 trucks per day and RF=1 for other roads. MEPDG Model (Level 2) Only for VERY heavy traffic scenario NOTATION: M RUP = 28-d flexural strength, s t and e t are tensile stress and tensile strain under cementitious layer, E = modulus of elasticity of cementitious layer

12. Rut Resistant Surfacing and Fatigue Resistant DBM The following provisions are made in the new guideline Higher viscosity grade bitumen or modified binder in surfacing VG-30 binder in DBM for traffic < 30 msa VG-40 binder in DBM for traffic > 30 msa DBM binder content in lower layer more than OBC by 0.5-0.6 % Air voids in bottom layer of DBM to be 3% Volume of bitumen increased to 13 % for DBM in lower layer

13. Drainage Layer Subbase should be composed of 2-layers Lower layer is a separation layer & upper later to be drainage layer Current trend is to limit fines upto 5 % (passing 75 micron) in India . However, new guideline calls for <2% fines Suggested permeability = 300 m/day DL may be treated with 2-2.5% bituminous emulsion to achieve compaction A filter fabric between sub-grade & DL may be required to prevent migration of fines from sub-grade into the voids of DL. The need should be assessed in each project. Based on target permeability and estimated infiltration, the thickness and grading of DL is determined (Refer Annex V for drainage design)

14. Drainage Layer Key Points for Effective DL Selection Avoid contamination Don’t block drainage path Avoid segregation

15. Pavement Design with RAP Why RAP ? Aggregates becoming progressively scarce Legal restriction on quarrying Construction activity expanded phenomenally Environmental concerns viz. disposal of dismantled material Pavement Design with RAP Bitumen emulsion or foamed bitumen treated RAP Suggested resilient modulus = 600 MPa (Range 600-1200) Poisson’s ratio = NOT GIVEN A four layer system comprising bituminous surfacing, treated RAP, cemented sub-base and sub-grade is proposed. Failure criteria are same as conventional flexible pavement How to determine the thickness of CTSB between 30-50 msa traffic not explained (See Plates 17,18,19,20)

16. Pavement Design Options The following design options are available in the new guideline Conventional 3 layer pavement structure same as IRC:37-2001 Five layer structure comprising cemented sub-base & base w/ aggregate interlayer for crack control Four layer structure comprising cemented sub-base & base w/ SAMI interlayer for crack control Four layer structure comprising cemented sub-base & treated RAP (treatment could be by foam bitumen or emulsion) Five layer structure comprising granular sub-base & cemented base w/ aggregate interlayer for crack control Four layer structure comprising cemented sub-base & WMM base IIT Pave software capable of handling 5-layer Burmister Model is adopted

17. Example Illustrating Design Method

18. Procedure for Calculating Design Traffic, N Estimate Traffic Growth Rate over Design Period, r Convert Axle Loads of Mixed Traffic into Equivalent No. of 80 kN Axle and Calculate VDF for Each Type of CV, F Use Presumptive VDF values, F Estimate Opening Year Traffic in Terms of AADT, A Estimate Lane Distribution Factor (D) for the Design Facility Axle load Data Available ? Calculate Design ESA, N as , Select Design Period, n No No N LDF  

19. Design Life Category IRC:37 IRC:58 2/4/6 Laning Manual Flexible Rigid One Time Construction Stage Construction National Highway State Highway 15 year Normally for 30 years Full Operation Period (FOP) BT for 10 yrs Granular for FOP Expressway & Urban Roads 20 years Other Categories 10-15 years Exceptionally for 20 years

20. Traffic Analysis (Cont’d) Vehicle Damage Factor - Example AASHTO load equivalence factors can used to convert traffic loads into equivalent 8160 kg single axle loads (using SN = 5 & pt = 2.5) 4 th Power Law

21. Traffic Analysis (Cont’d) Reference Axle Loads for Use with 4 th Power Damage Law LEF ij is the load axle type i with a loading of Wij , Po is the standard axle load (also called reference axle load) for the axle group type i and Wij is the axle load as measured during axle equivalency factor. Each axle load configuration such as single, tandem, tridem etc., has a reference standard axle as shown below: Axle Group Single axle single tyre (SAST) Single axle dual tyre (SADT) Tandem axle single tyre (TAST) Tandem axle dual tyre (TADT) Tridem axle dual tyre (TRADT) Reference axle load ( kN ) 65 80 90 148 224

22. Subgrade Characterization Compile CBR data Determine 90 th percentile CBR of Road bed Soil Determine effective Subgrade CBR As per IRC: 37-2012 Carry out Soil/Material Investigation Review available Soil Information of Project Road Classify Soil type along the Alignment -Determine CBR-Density-Moisture Relationship Establish CBR of Compacted Borrow Material Investigate Soil Borrow Areas

23. Subgrade Characterization Description of Subgrade Typical CBR Values Material USCS Classification Well Drained Poorly Drained Highly Plastic Clays CH 5 2-3 Silts ML             Silty Clay CL 6-7 4-5 Sandy Clay SC             Sand SW,SP 15-20 -

24. Design Principle - Traditional Pavement Failure Mode- Flexible Criteria Old Guideline New Guideline Fatigue cracking 20 % 10% for design msa > 30 20 % for design msa <30 Rut depth 20 mm 20 mm in 20 % length upto 30 msa 20 mm in 10 % length beyond 30 msa

25. Example of Use (Catalogue Method) Step 1: Traffic Calculation Total ESALs Buses + Trucks 20 million + 80 million = 100 million Step 2: Get CBR Value 90 th percentile CBR tests along the center line of Jhumritalaiya Road show: CBR ≈ 10 CBR of imported soil from nearby borrow areas CBR ≈ 10 Therefore design CBR = 10 % Step 3: Calculate Design Use Design Catalogue – Plate 7,pp 28

26. Example of Use (Cont’d) Required pavement structure Bituminous concrete = 50 mm DBM = 110mm WMM = 250 mm GSB = 200 mm

27. Analytical Model of a pavement structure subject to application of one standard axle of 80 kN Example of Use (Analytical Method)

28. Allowable values depend on the Materials properties and traffic expressed as a number of equivalent standard axles during the expected lifespan Two criteria are used for the Design: Vertical compressive strain at the top of the subgrade less than allowable values Horizontal tensile strain for bituminous layers or horizontal tensile stress for cement bound layers at the bottom of layers less than allowable values.

29. Dual Wheel Assembly Centre to centre distance between two wheels = 310 mm Standard Axle Load = 8160 kg (80 kN ) Load per wheel = 20 kN Tyre pressure, p = 5.6 kg/cm 2 =549.2 kPa Radius of wheel imprint = 10.79 cm, if p=560 kPa , and 9.54 cm if p=549 kPa Definition of Load

30. Material Characterization All materials are characterized by their elastic moduli (or resilient modulus) and Poisson’s ratios. A -layered elastic model (computer program IITPAVE) is used to compute stresses and strains.

31. Material Characterization (Cont’d) Sub-grade soil (in MPa )   E =10 x CBR ; for CBR less or equal to 5% E = 17.6 x CBR 0.64 ; for CBR greater than 5%   Modulus of unbound granular layer (in MPa )   E = 0.2 (h2) 0.45 x E 3 Where h 2 = thickness of the granular layer in mm and E 3 the underlying layer modulus

32. Resilient Modulus of Bituminous Mixes, MPa Mix type Temperature C 20 25 30 35 40 BC and DBM for VG10 bitumen 2300 2000 1450 1000 800 BC and DBM for VG30 bitumen 3500 3000 2500 1700 1250 BC and DBM for VG40 bitumen 6000 5000 4000 3000 2000 BC & DBM with Modified bitumen 5700 3800 2400 1650 1300 BM with VG30 bitumen 500 MPa at 35 C BM with VG40 bitumen 700 MPa at 35 C WMM/RAP treated w/ 3 % bitumen emulsion / foamed bitumen (2% residual bitumen & 1 % cementitious material) 600 MPa at 35 C (lab. values vary from 700-1200 MPa for water saturated samples) Note- Resilient modulus of BT layer at 35 C has been considered in the guidelines for pavement analysis (See Annexure I (I-8).

33. Desirable Properties of Cementitious Bases & Subbases Layer type Desirable Properties E (in MPa ) Poisson ratio Modulus of rupture Cement content Cemented subbase 2-4% UCS between 0.75 to 1.5 MPa for traffic < 10 MSA 400 0.25 UCS between 1.5 to 3 Mpa 600 (2000-3000) 0.25 Cemented Base E=k x UCS 28d Adopt 0.25 4-6% UCS of 4.5 MPa in 7-days 5000 0.20-0.25 20% of 28-d UCS UCS of 7 MPa in 7-days 7500 0.20-0.25 20% of 28-d UCS Note- high strength layers having 7-d UCS of 6-12 MPa given in Table 8 of IRC:SP-89-2010 are not recommended (See Annex-X) Close graded GSB material of MORTH w/ 53 mm maximum size of aggregate can be used k=1000-1250

34. IITPAVE INPUT

35. IITPAVE OUTPUT

36. Perpetual Pavement Definition - Flexible pavement with life > 50 year Research showed that: if tensile strain within bituminous layer < 70 micro-strain; then bituminous layer seldom cracks if vertical subgrade strain is < 200 micro-strain; then there will be no rutting of the subgrade Research also indicate that deep strength bituminous layers suffer damage only at top and no-where else In perpetual pavement, surface layer is the sacrificial layer

37. Perpetual Pavement

38. Thank you for your attention

39. Subgrade Characterization

40. Traffic Analysis (Cont’d) Annual Average Daily Traffic (AADT) Type of Commercial Vehicles Number of commercial vehicles (AADT) in the year 2011 Srinagar (km 19.5 of NH 79A) Gulabpura (km 80 of NH 79) Gangrar (km 160 of NH 79) Chittaurgargh bypass (km 187 of NH 79) Dabok (km 126 of NH 76) Bus 253 493 518 54 990 LCV 809 798 867 540 774 2 axle trucks 1485 1413 1684 759 847 3 axle trucks 4050 3845 4491 2042 2851 Multi axle vehicles 2971 2866 2942 1354 2344 Total 9568 9415 10502 4749 7806

41. Other Methods Each country has its own method Some countries have several methods Some popular methods are listed below AASHTO The Asphalt Institute Road Note 31, Road Note 29 AUSTROADS SHELL

42. Design for Stage Construction Granular crust to be designed for full operation period Initial bituminous crust to be designed for minimum 10 year period Future overlay (s) to extend life Initial overlay on existing pavement to be designed for minimum 10 year period

43. Mechanism of Load Transfer How Pavements Carry Loads Asphalt Layer Rigid Pavement Flexible Pavement Note- Concrete’s rigidity spreads the load over a large area and keeps pressures on the sub-grade low.

44. Material Characterization (Cont’d) Temperature °C 20°C 25°C 30°C 35°C 40°C BC & DBM for VG10 (Pen 80/100) bitumen 2300 1966 1450 1000 800 BC and DBM for VG30 (Pen 60/70) bitumen 3500 3000 2500 1700 1250 BC and DBM for VG-40 (Pen 30/40 bitumen) 6000 5000 4000 3000 2000 BM 80/100 bitumen       500   BM 60/70 bitumen       700  

45. Example of Use (Cont’d) Required pavement structure Bituminous concrete = 50 mm DBM = 140mm WMM = 250 mm GSB = 200 mm

46. Traffic Analysis (Cont’d) Traffic Loading in terms of MSA C = Cumulative number of axles during the design period for a given category of commercial vehicle. A = Opening year AADT (two directional) r = Annual rate of growth of a given commercial vehicle n = Analysis period in years VDF = Vehicle damage factor LDF = Lane distribution factor described in the preceding section. The formula is valid for a period of constant growth rate. The cumulative numbers for all constant growth rate period should then be added together. Finally, contribution of each category of commercial vehicle (viz., Bus, LCV, 2AT, 3AT & MAV) is added to derive cumulative msa .   N