THE GERMAN EMPIRICAL MECHANISTIC DESIGN SYSTEM PART I M - E ASPHALT PAVEMENT DESIGN IN GERMANY

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1 Fakultät Bauingenieurwesen Institut für Stadtbauwesen und Straßenbau Professur für Straßenbau THE GERMAN EMPIRICAL MECHANISTIC DESIGN SYSTEM PART I M - E ASPHALT PAVEMENT DESIGN IN GERMANY Sabine Leischner Frohmut Wellner NADim Seminar - Oslo TU Dresden

2 Design Guides in Germany Forschungsgesellschaft für Straßen und Verkehrswesen Arbeitsgruppe Infrastrukturmanagement Ausgabe 2012

3 Asphalt Pavements Surface layer Binder course Frost protection: Base course Entire thickness of pavement is dependent on: (Asphalt) - frost penetration - frost susceptibility of the soil in combination with Base course UGL/CTL - traffic load -between cm Sub base Surface layer Binder layer Base layer Base layer Sub grade

4 RStO 12- Table I, Part I LCC , t EASLs - B [Mio] > ,2 3, ,0 1,0 0.3 <0,3 1 Asphalt FPL (10) Asphalt CTB FPL Asphalt CTB FPL Asphalt CTB FPL

5 RStO Table I, Part II LCC t EASLs - B [Mio] > <0,3 3 Asphalt CRB FPL (10) 4 5 Asphalt GBC FPL Asphalt CRB/GBC FPL (10) (10)

6 Why a new mechanistic approach for pavement design?

7 Development of traffic

8 Development of traffic Prognosis 2050 Bill. t x km road freight transport rail transport waterway transport Year 2040 Source: Bast 2010

9 Standardised load classes Reality > 1 load class? Reality! 6 Load classes Load class [ Bk + max. ESALs]

10 Why? Technical background: - permanent increasing traffic load - climate change - limited resources - quality and costs of raw material Background by contract: - change of empirical to fundamental requirements in Germany - introduction of functional contracts

11 Forschungsgesellschaft für Straßen und Verkehrswesen Analytical Pavement Arbeitsgruppe Infrastrukturmanagement Design Guide + Software

12 Design criteria + frost protection! asphalt layers asphalt and cement treated layers σ D σ Βz σ v or σ v/ σ h h frost UGL σ v or σ v/ σ h FPL σ v or σ v/ σ h subbase/soil

13 Pavement Design Frost protection according to the RStO: Entire thickness of pavement is depended on: - frost penetration - frost susceptibility of the soil in combination with - traffic load

14 Input data traffic load climatic conditions stiffness fatigue resistance

15 Traffic loads in Germany permitted traffic loads heavy traffic: average of wheel contact pressure: 3,5 t.. 44 t weight of the vehicle 11,5 t axle load = 5,75 t wheel load 0,6... 0,8 MPa future: axle load 11,5 t 13 t (???) wheel contact pressure 0,8 MPa 1,0 MPa (???) number of car/trucks increasing continuously

16 Traffic loads in Germany Exceed of permitted axle loads [%] No. = kind of vehicle WIM, Federal Road Research Laboratory

17 Traffic loads in Germany Frequency [%] Traffic next to cities Continental traffic Mixed traffic Overloaded Axel load classes [t] Input: axle loads + frequency of load classes

18 Input data traffic load climatic conditions stiffness fatigue resistance

19 Surface temperatures -15 C +50 C

20 Temperature functions SL BC BC ,0-2,5 2,5 7,5 12,5 17,5 22,5 27,5 32,5 37,5 42,5 47,5-7,5 SBS

21 Frequency of appearance of temperature functions 25% 20% 15% 13,8% Climatic 9,9% Conditions 10% for 4 different Regions 5% 0,0% % 25% 1,3% 18,1% 19,3% 19,8% 8,0% S chles wig Hols tein A7, A210, A ,8% 3,2% 1,8% 0,0% 0,0% -13-7,5-2,5 2,5 7,5 12,5 17,5 22,5 27,5 32,5 37,5 42,5 47,5 25% 20% 15% 10% 5% 0% 0,0% 0,1% 17,8% 6,5% 20,1% 17,9% 16,3% 9,6% 4 Stationen (A7, A210, A215) 6 Stationen (A2) Niedersachsen A ,0% 3,8% 1,9% 0,0% 0,0% -13-7,5-2,5 2,5 7,5 12,5 17,5 22,5 27,5 32,5 37,5 42,5 47,5 20% 15% 10% 5% 0% 0,1% 1,1% 11,3% 17,2% 17,2% 16,8% 14,8% 9,0% Saarland A1,A6, A8, A ,7% 4,1% 2,7% Input: 0,0% 0,0% -13-7,5-2,5 2,5 7,5 12,5 17,5 22,5 27,5 32,5 37,5 42,5 47,5 25% 20% 15% 10% 5% 0% 6 Stationen (A1, A6, A8, A62) 1,7% 12,5% 17,9% 15,0% 30,2% Stationen (A8) 18,6% 14,0% 8,2% 5,3% Bayern A ,8% 2,9% 0,0% 0,0% < -13 C -2,5 C 7,5 C 17,5 C 27,5 C 37,5 C > 47,5 C temperature functions + frequency of appearance

22 Influence of temperature Temperature functions (examples) in the asphalt layers [MPa] Depth [mm] Temperature [ C] E= f(t) ABC BC SL ,0-2,5 2,5 7,5 12,5 17,5 22,5 27,5 32,5 37,5 42,5 47,5-7,5

23 Material behaviour Stiffness function Stiffness [N/mm²] ABC 3 ABC 1 ABC Temperature [ C]

24 Temperature and Stiffness E-Modulus Stiffness fuction function according according to the to temperature the temperature distribution [MPa] depth [mm] Depth [mm] E-modulus [N/mm²] - 12,5 C - 7,5 C - 2,5 C 2,5 C 7,5 C 12,5 C 17,5 C 22,5 C 27,5 C 32,5 C 37,5 C 42,5 C 47,5 C Based on this => calculation of stresses/strains

25 Input data traffic load climatic conditions stiffness fatigue resistance

26 Which test? Triaxial test Direct tension test Indirect tension test? Four point bending beam

27 Indirect tension tests -simple test -simple to make the sample (laboratory + in situ!) -low effort for sample preparation

28 Stiffness Stiffness-Modulus [MPa] Function according to Francken/Verstraeten f = 10 Hz Function according to test results (indirect tensile test) Input: Temperature [ C] Stiffness modulus - temperature functions

29 Material behaviour Load cycles Fatigue functions! AL Sp-Asphalt Input: fatigue functions Initial elastic strain [ ]

30 Calculation 13 temperature conditions load classes I II III IV V XIII. I II III IV V X 13 ( 200) * 10 (10 20) = 130 (4000) strain conditions evaluation: permitted N = F(calculated ε) per condition accumulation: Miner s law

31 Accumulation of damages (test results) per N = f ( exp σ,γ) (input data's) exp N Miner = exp N exp N exp N n pern pern pern 1 2 n 1 exp expected per - permitted Miner s law 1*100 = 100% = Fatigue status

32 Design Similar approach for UGL, CTB Fatigue status [%] Required service life [years]

33 Examples Design criterion Fatigue

34 Example 1 - material behaviour Stiffness determined by indirect tensile test Stiffness [N/mm²] ABC 3 ABC 1 ABC Temperature [ C]

35 Example 1 - material behaviour Fatigue functions - determined by indirect tensile test Load cycles N [-] ABC 2 ABC 3 ABC ,01 0,10 1,00 Initial elastic strain [ ]

36 Effect of material behaviour Ermüdungsstatus [%] Fatigue status [%] a 30 a 15 a origin Provenienz A A origin Provenienz B B origin Provenienz C C 0 Level of fatigue of asphalt base course material with the same stone material and sieving curve and Bitumen 50/70 with different origin

37 Example 2 traffic load Frequency [%] Traffic next to cities Continental traffic Mixed traffic Axel load classes [t]

38 Example 2 traffic load = 8 cm Effect on service life? B > 32 Mio 10 t StdA +0-4 cm +0 cm cm 4 cm SL 4 cm SL 4 cm SL 4 cm SL 8 cm BL 22 cm ABC 8 cm BL +200% = 90 a 18 cm ABC 8 cm BL 22 cm ABC 8 cm BL -50% =15 a 26 cm ABC 44 cm SBS 42 cm SBS 47 cm SBS 50 cm SBS RStO Mio 10 t StdA 90 Mio 10 t StdA 220 Mio 10 t StdA

39 Example 3 Performance based mix design method

40 Research project - Number of asphalt mixes - Grading curve Bitumen Producer medium No. of Bitumen content coarse fine Asphalt mixes

41 Grading curve (asphalt base course) fine medium coarse

42 Stiffness-Temperature-Function Stiffness [ MPa] MPa MPa Temperature [ C]

43 Fatigue function Load cycles cycles cycles Initial elastic strain [ ]

44 Calculation according to RDO Asphalt 09 B = 32 Mio ESALs 4 cm SL 8 cm BC 22 cm ABC 56 cm UGL RStO 12

45 Layer thickness Binder content Permitted Tolerances of Bitumen Content [%] Number of test results Layer adjusment [cm] ZTV Asphalt- StB 07/13 Method to determine the bitumen content for asphalt mixes? Bitumen content [M.-%]

46 Layer thickness Binder content Layer adjustment [cm] Minimum = 5% Bitumen content [M.-%]

47 Expenses [ /m²] Binder content [%] Minimum = 4,5 %! /m² Bitumen content [M.-%]

48 Example 3 - Layer bond Dynamic shear test 1,0 mm

49 Example 3 - Layer bond F S σ N b A

50 Results Layer bond Shear stiffness G s [MPa/mm] Temperature T [ C] Frequency f (x2) [Hz] Normal stress σ N [kpa] No. 0 Frequency [Hz] Temperature [ C] Gs,m (200 g/m^2) [MPa/mm] Gs,m (400 g/m^2) [MPa/mm] Gs,m (300 g/m^2) [MPa/mm] Normal stress [kpa]

51 Results Layer bond Sigmoidal function = ( G G ) s,max s,min G s Gs,min + [ m ( c ln σ + d ) + ( j σ + k )] 1+ e N N

52 Example 3 - Layer Bond 100% Load Load classification Classification < Mio Mio t StdA t ESALs ,9 15,6 22, % 80% 70% Fatigue Status [%] Fatigue status [%] 60% 50% 40% 30% 20% 10% 0% Service life [Years] Service life [Years]

53 Future? Improve the models to describe the material behavior: - Asphalt: viscos-elastic (complex modulus) + plastic behavior - Unbound materials: nonlinear-elastic + plastic behavior - more detailed temperature functions - Finite element method instead of multi layer theory - probabilistic instead of deterministic predictions

54 The End Thank you for your attention!