Easy-To-Use Perpetual Pavement Design Software Rocky Mountain Asphalt Conference February 25, 2010 Dr. David Timm, P.E. Department of Civil Engineering Auburn University
What is a Perpetual Pavement? A pavement designed so there are no distresses deep in the pavement structure
Limit Cracking to top-down
Goal of Perpetual Pavement Design Design so there are no deep structural distresses Bottom up fatigue cracking Structural rutting All distresses can be quickly remedied from surface Result in a structure with Perpetual or Long Life
Designing Perpetual Pavements Newcomb, 2001
M-E Perpetual Pavement Design P Log A Threshold Strain t D 1 E 1 D 2 E 2 Log N No Damage Accumulation v D 3 E 3
Strain, (10E-06) 1200 1000 800 600 400 200 0 Normal Range for Fatigue Testing Endurance Limit 1000 100000 10000000 1.1E+08 Number of Loads to Failure Normal Fatigue Testing Results Versus Endurance Limit Testing
What is the Endurance Limit for HMA? 1972 Monismith estimates about 70 2001 I-710 designed at 70 2002 70 used by APA 2007 NCHRP 9-38 Lab Study 100 for unmod binders 250 for mod binders More severe than field 2007 MEPDG uses 100 to 250 2008 Field measurements show higher strains
N8 and N9 0.0 Lift 1 N8 Section SMA N9 2.3 PG 76-28 2.0 Lift 1 Depth From Pavement Surface, in. 5.0 10.0 15.0 20.0 25.0 Lift 2 Lift 3 Lift 4 2.9 PG 76-28 3.5 2.8 1.9 6.4 Moisture Content = 10.8% Unit Weight = 133.4 pcf Moisture Content = 18.0% Unit Weight = 126.2 pcf Dense Graded HMA Dense Graded HMA PG 64-22 Rich Bottom Layer PG 64-22 Aggregate Base (Track Fill) Subgrade (A-7-6 Soil) 3.1 2.6 3.2 8.4 Moisture Content = 12.9% Unit Weight = 133.8 pcf Moisture Content = 17.2% Unit Weight = 126.9 pcf Lift 2 Lift 3 Lift 4 Lift 5
Strain Measurements
1200 1000 800 600 400 200 0 Strain and Temperature 01-Nov-06 31-Dec-06 01-Mar-07 30-Apr-07 29-Jun-07 28-Aug-07 27-Oct-07 26-Dec-07 24-Feb-08 24-Apr-08 Date 120 100 80 60 40 20 0 Longitudinal Microstrain-Single Axle Mid-Depth Pavement Temperature,F N8-Temperature N9-Temperature N8-Strain N9-Strain
Strain vs. Temperature 1200 Longitudinal Microstrain-Single Axle 1000 800 600 400 200 0 Section Axle Type C 1 C 2 R 2 Single 21.249 0.033 0.96 N8 Tandem 15.326 0.035 0.96 Steer 11.341 0.036 0.87 Single 11.136 0.029 0.93 N9 Tandem 8.600 0.030 0.92 Steer 5.901 0.030 0.93 N8 Strain = 21.249e 0.033*Temp R 2 = 0.9584 N9 Strain = 11.136e 0.0293*Temp R 2 = 0.9309 0 20 40 60 80 100 120 140 Mid-Depth Pavement Temperature, F
1400 1200 1000 800 600 400 200 0 Strain History Section N8 11/1/2006 12/1/2006 12/31/2006 1/30/2007 3/1/2007 3/31/2007 4/30/2007 5/30/2007 6/29/2007 7/29/2007 8/28/2007 9/27/2007 10/27/2007 Time 140 120 100 80 60 40 20 0 Longitudinal Microstrain-Single Axles Temperature, F Temperature Strain
Strain Distributions 100% 90% 80% 70% N9 N8 Percentile 60% 50% 40% 30% 20% 10% 0% 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 Longitudinal Strain
NCAT Test Track Results 100% Percentile 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Fatigue Cracking 0 200 400 600 800 1000 1200 N1 2003 N2 2003 N3 2003 N4 2003 N5 2003 N6 2003 N7 2003 N1 2006 N2 2006 N3 2006 N4 2006 N8 2006 N9 2006 N10 2006 S11 2006 S13 2000 Microstrain
PerRoad 3.3 Sponsored by APA Developed at Auburn University / NCAT M-E Perpetual Pavement Design and Analysis Tool
Environmental Conditions Variability and Thresholds Layer Properties
f Material Properties f Thickness
Performance Criteria Location in Layer Pavement Response Threshold Transfer Function
Axle Weight Distribution Traffic Volume Types of Axles
Functional Classification Vehicle Frequency Number of Axles
Damage Accumulation Design Life Percent Below Threshold
PerRoadXPress For Low Volume Roads
Methodology - Overview Develop a set of boundary conditions Execute PerRoad analysis to determine required thickness for each design Develop design regression equations Guiding Principles Limit number of required inputs Make design procedure simple/efficient
Traffic Parameters Rural (Local) Collector vs. Urban Collector Volume 500, 1000 and 5000 AADT 0%, 1% and 3% Growth 1%, 5%, 10% and 20% Trucks Distribution Factors Assume 2-lane facility 100% Trucks in design lane 50% directional distribution Loadings Default Load Spectra in PerRoad Volume Range (over 30 years) 27,375 to 8,577,500 trucks
Structural Cross Section Layer Stiffness Poisson s Ratio HMA 400,000 to 1,000,000 psi 0.35 Variable Aggregate Base 20,000 psi 0.40 0-10 in. 10,000 psi to 30,000 psi Subgrade Soil 0.45 Infinite
Number of Simulations # Simulations = X X X X X X 2 Highway Classifications 3 Traffic Volumes 3 Growth Rates 4 Percent Trucks 3 Soil Stiffnesses 3 HMA Stiffnesses 3 Base Thicknesses 1,944 Pavement Designs
Design Equation HMA = C 0 + C 1 *AADT + C 2 *%Trucks + C 3 *%Growth + C 4 *Soil Stiffness + C 5 *Base Thickness + C 6 *HMA Stiffness
PerRoad XPress Traffic Soil Agg. Base HMA
AASHTO vs. PerRoad 30 25 AASHTO-93 PerRoad HMA Thickness, in. 20 15 10 5 HMA (a 1 = 0.44) 6 Agg. Base (a 2 = 0.14) Subgrade (M r = 15,000 psi) 0 1 10 100 1000 Traffic, million ESALs