Fatigue Endurance Limits for Perpetual Pavements

Fatigue Endurance Limits for Perpetual Pavements By Waleed Zeiada, Ph.D. November 14, 2013 Civil, Environmental, and Sustainable Engineering Tempe, AZ 85287 5306 1

Outline Background Research Statement and Objectives Testing Plan and Design of Experiment Endurance Limit (EL) Algorithm Development Development of SR Models Comparison of EL from Uniaxial and Beam Fatigue Incorporating EL Methodology into AASHTOWare-ME Conclusions, and Recommendations 2

Outline Background Research Statement and Objectives Testing Plan and Design of Experiment Endurance Limit (EL) Algorithm Development Development of SR Models Comparison of EL from Uniaxial and Beam Fatigue Incorporating EL Methodology into AASHTOWare-ME Conclusions, and Recommendations 3

Background Fatigue Hot Mix Asphalt Endurance Limit Perpetual Pavement 4

HMA Fatigue Damage/Cracking Definition: A load associated damage due to repeated traffic loading. Description: Three different stages Early Stage Intermediate Stage Final Stage 5

Perpetual Pavements Definition: Term used to describe a long lasting HMA pavements. At least 50 years Full depth asphalt, 1960s Three HMA layer system Increases pavement recycling Cost savings Environmental benefits. 6

Definition: Wöhler (1870) Endurance Limit 7

Does HMA Exhibit an Endurance Limit? Monismith et al., 1970 Carpenter et al., 2003 HMA EL (Prowell et al., 2009): Strain level yields 50 millions load repetitions until failure 8

Perpetual Pavement Design Concept Endurance Limit = 75 ms 9

Outline Background Research Statement and Objectives Testing Plan and Design of Experiment Endurance Limit (EL) Algorithm Development Development of SR Models Comparison of EL from Uniaxial and Beam Fatigue Incorporating EL Methodology into AASHTOWare-ME Conclusions, and Recommendations 10

Research Problem Statement and objectives The EL concept has not been totally implemented in AASHTOWare Pavement ME Design software No current methodology to consider the effect of the environmental conditions, traffic condition, mix design, and material properties together in the EL calculations Develop an algorithm to determine EL that is compatible with the AASHTOWare-ME software 11

New EL Definition EL is a result of a balance of damage caused by loading and healing or damage recovery that occurs during rest periods T6 T5 T4 T3 T2 T1 A 12

Outline Background Research Statement and Objectives Testing Plan and Design of Experiment Endurance Limit (EL) Algorithm Development Development of SR Models Comparison of EL from Uniaxial and Beam Fatigue Incorporating EL Methodology into AASHTOWare-ME Conclusions, and Recommendations 13

Factors Affecting Fatigue and EL Asphalt Content (%) Air Voids (%) Temperature ( o F) Rest Period (seconds) Tensile Strain (μs) Factors Binder Grade Aggregate Type Filler Percent Aggregate Gradation Test Type 10 Factors with 3 levels: 3^10 = 59049 tests Three replicates: 69049 * 3 = 177147 tests Assuming average of 10 hours per test Total of 202 years 14

Selected Factors Factors No. of Levels Asphalt Content, AC (%) 4.2, and 5.2 Air Voids, Va (%) 4.5, and 9.5 Temperature, T ( o F) 40, 70, and 100 Rest Period, RP (seconds) 0, 5, 1, and 10 Tensile Strain, ε t (μs) L, M, and H Binder Type PG 58-28, 64-24, and 76-16 15

Test Type Beam Fatigue Test Uniaxial Fatigue Test 16

Binder Type PG 58-28 PG 64-22 PG 76-16 Binder Content 4.2 5.2 4.2 5.2 4.2 5.2 Air Voids (%) 4.5 9.5 4.5 9.5 4.5 9.5 4.5 9.5 4.5 9.5 4.5 9.5 Temperature, F Tensile Strain Rest Period (sec) 40 70 100 L M H L M H L M H 0 U U U 1 5 U U U U 10 0 U U U 1 U 5 U U U 10 U 0 U 1 U 5 U 10 0 U U U 1 5 U U U 10 U 0 U U U 1 U 5 U U U U 10 0 1 U 5 10 0 U U U 1 U U 5 U U 10 0 U U U 1 5 U U U 10 U 0 U 1 5 U 10 Total Number of Combinations Beam Fatigue = 190 Uniaxial Fatigue = 51 17

Outline Background Research Statement and Objectives Testing Plan and Design of Experiment Endurance Limit (EL) Algorithm Development Development of SR Models Comparison of EL from Uniaxial and Beam Fatigue Incorporating EL Methodology into AASHTOWare-ME Conclusions, and Recommendations 18

Strain Stiffness Ratio Strain Healing of Micro-cracks 1.2 Time 1 SR = 1.0, No Fatigue Damage 1-SR WRP Test Without Rest Periods 0.8 Healing 1-SR WORP 0.6 Time 0.4 0.2 Without Rest Period With Rest Period Test With Rest Periods 0 0 5000 10000 15000 20000 25000 19 Number of Loading Cycles

Stiffness Ratio Stiffness Ratio Algorithm Development for HMA Endurance Limit Determination of Endurance Limit Using SR 1.2 1.0 At endurance limit, SR = 1.0 0.8 0.6 5.2AC%, 9.5Va%, 112.5 με, 5 sec RP 5.2AC%, 9.5Va%, 155 με, 5 sec RP 1 0.4 0 5000 10000 15000 20000 Loading Cycles, N 0.8 0.6 EL = 80 μs 0.4 10 100 201000 Tensile Strain, μs

Outline Background Research Statement and Objectives Testing Plan and Design of Experiment Endurance Limit (EL) Algorithm Development Development of SR Models Comparison of EL from Uniaxial and Beam Fatigue Incorporating EL Methodology into AASHTOWare-ME Conclusions, and Recommendations 21

Stiffness Ratio First Generation SR Model SR = f (T, AC, V a, ε t, RP, BT, and N) AC = Asphalt content, % V a = Air voids, % ε t T RP = Tensile Strain, μs = Temperature, o F = Rest period, sec 1.00 0.98 0.96 N = 5,000 N = 10,000 N = 15,000 N = 20,000 BT = Binder Type 0.94 N = Number of cycles 0.92 0.90 0 5000 10000 15000 20000 2225000 Number of Loading Cycles

PSR First Generation SR Model Form of First Generation SR Model Effect of Rest Period 1.0 0.8 0.6 0.4 0.2 0.0 PSR = a + b * Tanh (c * RP) a, b, and c are regression coefficients 0 1 2 3 4 5 6 7 8 9 10 11 RP, Second 23

R 2 adj = 0.979 First Generation SR Model SR = 0.1564774 + (0.00079*BT) + (0.070059744*AC) + (0.00393*V a ) +(0.10095*RP) - (1.268*10-7 *N f ) - (0.0024676 *T) - (0.0001677*BT*AC) + (3.29961x10-5 *BT*RP) + (3.488*10-6 *BT*T) + (0.00794848*AC*RP) - (0.0042225*V a *RP) + (0.0006044*AC*T) - (0.0001035*V a *T) - (2.889*10-8 *RP*N f ) + (2.9191*10-9 *N f *T) - (0.0025*RP*T) - (3.97*10-7 *BT 2 ) - (1.20135*10-5 *T 2 ) + (8.434*10-8 *BT 2 *AC) - (2.8756*10-8 *BT 2 *RP) + (1.9558*10-6 *AC*T 2 ) + (6.6137*10-7 *V a *T 2 ) - (1.582*10-11 *N f *T 2 ) + (1.262x10-5 *RP*T 2 ) - (1.176*10-6 *V a *RP*T 2 ) + (3.124*10-12 *N f *RP*T 2 ) - (7.4*10-7 *BT*AC*T) + (3.92*10-7 *BT*RP*T) + (0.00013185 *V a *RP*T) + (2.19 * 10-9 *N f *RP*T) 24

SR EL Values From First Generation SR Model 1.0 0.9 PG 64-22 70⁰F 0.8 4.5 Va% - 5.2 AC% 9.5 Va% - 5.2 AC% 4.5 Va% - 4.2 AC% 9.5 Va% - 4.2 AC% 0.7 10.0 100.0 Tensile Strain, εt 1000.0 25

4.2AC-9.5Va 4.2AC-4.5Va 5.2AC-9.5Va 5.2AC-4.5Va 4.2AC-9.5Va 4.2AC-4.5Va 5.2AC-9.5Va 5.2AC-4.5Va 4.2AC-9.5Va 4.2AC-4.5Va 5.2AC-9.5Va 5.2AC-4.5Va Endurance Limit, ms EL Values From First Generation SR Model 300 250 40 ⁰F 70 ⁰F 100 ⁰F 200 150 100 50 0 PG 76-16 PG 64-22 PG 58-28 26

Second Generation PSR Model BT, T, AC, V a were replaced by initial stiffness, E o R 2 adj = 0.891 SR = f (E o, ε t, RP, and N) SR=2.0844-0.1386*log(E o )- 0.4846*log(e t )-0.2012*log(N)+ 1.4103*tanh(0.8471*RP)+0.0320 *log(e o )*log(e t )-0.0954*log(E o ) *tanh(0.7154*rp)- 0.4746*log(e t )*tanh(0.6574*rp) +0.0041*log(N) *log(e o )+0.0557*log(N)*log(e t )+ 0.0689*log(N)*tanh(0.0259*RP) 27

SR Second Generation SR Model 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 RP = 5 sec, N = 200,000 10 100 1000 e, ms Eo=50 ksi Eo=100 ksi Eo=200 ksi Eo=500 ksi Eo=1000 ksi Eo=2000 ksi Eo=3000 ksi 28

Endurance Limit, ms EL from Second Generation SR Model 250 200 150 100 50 0 1 2 5 10 20 Rest Period, sec Eo=3000 ksi Eo=2000 ksi Eo=1000 ksi Eo=500 ksi Eo=200 ksi Eo=100 ksi Eo=50 ksi 29

Outline Background Research Statement and Objectives Testing Plan and Design of Experiment Endurance Limit (EL) Algorithm Development Development of SR Models Comparison of EL from Uniaxial and Beam Fatigue Incorporating EL Methodology into AASHTOWare-ME Conclusions, and Recommendations 30

Stiffness Ratio Stiffness Ratio Beam Fatigue Versus Uniaxial Fatigue Tests 1.2 1.0 0.8 0.6 0.4 Beam Fatigue Uniaxial Fatigue Damage Comparison 0.2 0.0 (a) 4.5 Va% - 4.2 AC% 100 Tensile με, 40 F 4.5 Va% - 4.2 AC% 0 50000 100000 150000 1.1 100 Tensile με, 40 F 5 sec. RP Number of Loading Cycles 1.2 1.0 Healing Comparison 0.9 0.8 0.7 0.6 0.5 0.4 Uniaxial Fatigue without RP Uniaxial Fatigue with RP Beam Fatigue without RP Beam Fatigue with RP Uniaxial Fatigue Healing Beam Fatigue Healing 0 2000 4000 6000 8000 10000 12000 Number of Loading Cycles 31

Uniaxial Fatigue Endurance Limit Uniaxial Fatigue Versus Beam Fatigue 1000 100 y = 0.8986x R² = 0.9688 10 10 100 1000 Beam Fatigue Endurance Limit 32

Outline Background Research Statement and Objectives Testing Plan and Design of Experiment Endurance Limit (EL) Algorithm Development Development of SR Models Comparison of EL from Uniaxial and Beam Fatigue Incorporating EL Methodology into AASHTOWare-ME Conclusions, and Recommendations 33

Dynamic Modulud, E* psi Incorporation of EL into AASHTOWare-ME 1. Calculation of Endurance Limit SR = f (E o,e t, N, and RP) 1.0E+08 E o, Initial Stiffness (ksi) N = Number of cycles N of 20,000 is recommended RP= Rest Period (sec) RP = t / (NT) 1.0E+07 1.0E+06 1.0E+05 1.0E+04-10.00-5.00 0.00 5.00 10.00 Log Reduced Frequency, Hz e t, Tensile Strain, μs Tensile Strain is equal to the Endurance Limit at PSR = 1.0 34

Incorporation of EL into AASHTOWare-ME 2. Incorporation of EL into Fatigue Damage D i = Σ (n i / Nf i) D = Fatigue Damage n i = Actual traffic for period i (Traffic Demand) Nf i = Allowed Traffic in period i (Traffic Capacity) e t If the calculated EL < the actual e t, Damage is count If the calculated EL the actual e t, the Ni is infinity and the Damage is zero 35

Outline Background Research Statement and Objectives Testing Plan and Design of Experiment Endurance Limit (EL) Algorithm Development Development of SR Models Comparison of EL from Uniaxial and Beam Fatigue Incorporating EL Methodology into AASHTOWare-ME Conclusions, and Recommendations 36

Conclusions HMA exhibits endurance limit Mixtures using softer binders exhibit higher endurance limits than mixtures using stiffer binders High binder contents and low air voids produced the high endurance limit values Endurance limit values were higher at high temperatures The endurance limit values from the beam fatigue exhibit similar trends compared to those of the uniaxial fatigue test The endurance limits obtained in this study can be incorporated in the AASHTOWare-ME 37

Field calibration is needed Recommendations Consider other types of aggregates, and mixes such as warm mix asphalt, asphalt rubber, and polymer modified mixtures 38

Acknowledgement NCHRP 944-A Project Panel ASU Project Team and Lab Support: Dr. Matthew Witczak Dr. Michael Mamlouk Dr. Kamil Kaloush Dr. Mena Souliman Mr. Peter Goguen, and Mr. Kenny Witczak IPC: Mr. Con Sinadinos, Mr. Alan Feeley, and Mr. Stephen King 39

Questions! 40