1. Quality Control/Quality Assurance of Asphalt Mixtures Using Surface Wave Methods Shibin Lin, PhD Student Jeramy Ashlock, Major Professor (PI) Christopher Williams (CoPI) Hosin (David) Lee (CoPI) 2013 Mid-Continent Transportation Research Symposium Department of Civil, Construction, and Environmental Engineering I OWA S TATE U NIVERSITY

2. Significance of the Proposed Study Quality Density Density change overnight after paving: slight increase for seven projects, slight decrease for three projects. (Hanna, et al. 2008 from University of Wisconsin-Madison) Density (Hanna, et al. 2008 ) 2/29

3. Significance of the Proposed Study Quality Stiffness or Modulus e.g. Arellano et al., 2003, from Texas DOT Williams, et al., 2007, from ISU. Von Quintus et al., 2009, from ARA, INC. Structural property Performance Stress (Force) Strain (Displacement) Modulus (Stiffness) G=ρV s 2 Shear modulus: 3/29

4. Outline I.Equipment 1)PaveTracker (dielectric constant  Density) 2)GeoGauge (mechanical impedance, force over deflection  Stiffness) 3)Custom-built surface wave testing equipment (wave speed  G=ρV s 2 ) II.Testing Boone Central Iowa Expo project(36 base cores, 16 surface cores) III.Results 1)Density 2)Wave speed 3)Stiffness 4)Correlations IV.Preliminary conclusions V.Future works 4/29

5. GeoGauge (Humboldt) Equipment PaveTracker (Troxler) Custom-built surface wave testing equipment (Lin&Ashlock) 5/29

6. Surface wave method Surface wave methods make use of the dispersive nature of Rayleigh waves, which means that different frequency components of a wave travel at different phase velocities. FEM simulation of a transient impact Dispersive nature of Rayleigh waves Phase Velocity Frequency Dispersion curve Layer thickness and stiffness 6/29

7. Surface wave method By measuring the experimental phase velocity versus frequency relation (termed the experimental dispersion curve or dispersion image), the material properties can be calculated in the form of layer thickness and moduli. 7/29

8. Surface wave method Data acquisition and analysis system programmed in MATLAB 8/29

9. Surface wave method joint between two lanes middle of one lane (2012, in HWY 61 Fort Madison) The joint has lower wave speed and thus lower quality than the centerline. 9/29

10. Testing AsphaltBoone Central Iowa Expo project Base36 cores Surface16 cores 10/29

11. Results: PaveTracker Density 36 base cores (4”) from Boone σ/μ7.4×10 -4 2.5×10 -3 3.7×10 -4 3.4×10 -4 Hot = 1 to 3 hours after paving, Cold = next day (same locations) Increase in scatter and slight decrease in avg. density overnight 11/29

12. Results: SWM Wave speed SWM testing of Core 1-1 HOTCOLD Rayleigh waves are faster in cold asphalt pavements than in hot ones 12/29

13. Results: SWM Wave speed 36 base cores (4”) from Boone The dispersion images of cold asphalt pavements have wider frequency and velocity ranges than those of hot ones Pick Rayleigh wave velocities at 230 Hz of “hot” dispersion images and at 2500 Hz of “cold” dispersion images for further study HOTCOLD 13/29

14. Results: SWM Wave speed σ/μ 7.2 10.0 Velocity much more sensitive than density for assessing thermal effects Due to large change of modulus w/temperature, “Cold” velocities should correspond to modulus from lab tests 36 base cores (4”) from Boone 14/29

15. Results: Correlation between Lab Density Methods 36 base cores (4”) from Boone SSD density is highly correlated to CoreLok density 15/29

16. Results: PT Density vs. Lab Density HOT COLD 36 base cores (4”) from Boone High correlation between “hot” PT density and Lab density Low correlation between “cold” PT density and Lab density 16/29

17. Results: SWM Velocity vs. Field/Lab Density HOT COLD V s = (G/ρ) 1/2 COLD Very small correlation between PT density and wave speed Low correlation between PT density and wave speed 17/29

18. V s 2 = G/ρ Results: SWM Velocity vs. Lab Density COLD 18/29

19. Results: Air voids, Temperature difference As air voids increases, wave speeds decrease As temperature differences increase, wave speed differences increases As temperature differences increase, density differences first decrease and then increase. 19/29

20. Results: PaveTracker Density 16 surface cores (2”) from Boone Hot = 4 to 7 hours after paving, Cold = next day (same locations) Increase in scatter and slight decrease in avg. density overnight σ/μ1.7×10 -4 9.5×10 -4 1.6×10 -4 20/29

21. Results: PT Density vs. Lab Density 16 surface cores (2”) from BooneHOT COLD Low correlation between “hot” PT density and Lab density Very small correlation between “cold” PT density and Lab density 21/29

22. Results: SWM Wave speed 16 surface cores (2”) from Boone σ/μ1.96.7 Velocity much more sensitive than density for assessing thermal effects Due to large change of modulus w/temperature, “Cold” velocities should correspond to modulus from lab tests 22/29

23. Results: SWM Velocity vs. Field/Lab Density 16 surface cores (2”) from BooneHOT COLD Very small correlation between Field/Lab density and wave speed 23/29

24. Results: SWM Velocity vs. Lab Density 16 surface cores (2”) from Boone COLD 24/29

25. Results: GeoGauge stiffness 16 surface cores (2”) from Boone σ/μ0.460.74 Stiffness much more sensitive than density for assessing thermal effects 25/29

26. Results: SWM Velocity vs. GeoGauge stiffness 16 surface cores (2”) from Boone HOT COLD The correlation between SWM velocity and GeoGauge stiffness of cold asphalt is higher than the correlation between SWM velocity and GeoGauge stiffness of hot asphalt. 26/29

27. Results: Temperature difference 16 surface cores (2”) from Boone Density difference has the lowest correlation to temperature difference As temperature differences increase, wave speed and stiffness differences increases 27/29

28. Preliminary conclusions 1.Density slightly decreases overnight as pavement cools 2.Stiffness and wave speed significantly increase overnight, due to setup causing increase in stiffness/modulus 3.Wave speed is not good indicator of density due to stronger dependence on modulus, which varies by orders of magnitude 4.Wave speed can be a useful quantitative index for QA/QC based on pavement stiffness/modulus: V s highly sensitive to modulus, temperature Clear differences found in pavement joints vs. centerline 28/29

29. Future work 1.Tests on 24 more cores from four highways in Iowa. 2.More data for verifying preliminary conclusions for different pavement types (CIR, FDR, overlay, modified binders). 3.Modulus measurement in laboratory and correlation to field velocity (at same temperature). 4.More sophisticated SWM testing equipment and software. 5.Quantitative quality index based on wave speed. 29/29

30. Thanks! Questions?