Verification of Gyration Levels in the Superpave

Transcription

1 Verification of Gyration Levels in the Superpave N design Table NEAUPG Newport, Rhode Island Brian D. Prowell, P.E.

2 The compaction effort used in a volumetric mix design should produce laboratory samples which approximate the ultimate density of the pavement The goal of this project is to verify the laboratory compaction efforts established in 1999 for the Superpave gyratory compactor

3 Overview Background of N design NCAT Test Track NCHRP 9-9(1) 9 9(1) Field Test Sections Affect of Internal Angle of Gyration Conclusions

4 SHRP N design Experiment Looked at three traffic levels and three climates, two replicates for each except hot climate (nine cells) Sites selected from LTPP GPS pavement sites 12 years old or older - reached design air voids of 3% - 5% Construction air voids assumed to be 8%

5 SHRP N design Experiment Cont. Fifteen 12 inch diameter cores were taken, one from each project. Asphalt was extracted Recovered aggregate re-mixed with virgin AC-20 Aged for four hours Compacted to 230 gyrations (design levels were back calculated).

6 Original SGC Compaction Effort Design Average Design High Air Temperature ESALs <39 ºC ºC ºC ºC millions) N N N N ini des max ini N des N max N ini N des N max N ini N des? ? N max

7 National Efforts to Address N design Asphalt Institute - N design II Experiment Examined field densification of SPS-9 9 pavements Looked at mixture stiffness (G*) with SST NCAT - NCHRP Evaluation of the SGC Procedure Looked at sensitivity of mix volumetrics to changes in N design A new N design Table was developed from each effort

8 SGC Compaction Effort 1999 ESAL s N ini N des N max App < Light 0.3 to < Medium 3 to < * 160 High 10 to < High > Heavy Base mix (< 100 mm) option to drop one level, unless the mix will be exposed to traffic during construction.

9 Thoughts on N design Laboratory compaction effort should produce sample density approximately equal to ultimate pavement density Ultimate pavement density believed to be reached after years of traffic Typically, select laboratory density of 96% of Theoretical maximum density or 4% air voids Too little air voids (<2%) results in rutting Too many air voids tend to cause durability problems

10 NCAT Test Track near Auburn, Alabama U.S.A. Lee County Road 151 Laboratory Asphalt Plant North 2.74 km Oval Test Track on 309 acres 46 Cooperatively Sponsored 61 m Test Sections 437 sq m Testing Laboratory 242 sq m Truck Maintenance Facility

11 SECTION LAYOUT N W1 W2 W3 W4 W5 W6 W7 W8 W9 N13 N12 N11 N10 N9 N8 N7 N6 N5 N4 N3 N2 N1 W10 S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 S11 S12 S13 E10 E1 E9 E2 E8 E3 E7 ONSITE LAB AND TRUCK MAINTENANCE E6 E4 E5 HMA PLANT

12 NCAT Test Track Average Densification PG Upper Lift R 2 = 0.98 PG Lower Lift R 2 = 0.96 Pavement Density, % Gmm PG Upper Lift R 2 = 0.98 PG Lower Lift R 2 = 0.99 Winter PG Lower Lift PG Lower Lift PG Upper Lift PG Upper Lift ESALs

13 Estimation of Density at a Given Gyration Level Density at Gyration X? Density at NDesign? Height at NDesign Height at Gyration X

14 NCAT Test Track - Design Gyrations to Meet Pavement Density Design Gyrations Winter PG Lower Lift R 2 = 0.87 PG Upper Lift R 2 = 0.97 PG Lower Lift R 2 = 0.95 PG Lower Lift PG Upper Lift R 2 = 0.94 PG Lower Lift PG Upper Lift Note: Samples compacted on Troxler Compactor PG Upper Lift ESALs

15 The Whole Truth Predicted Gyrations to Match Test Track Density 140 Test Track Unmodified AC Predicted Gyrations to Meet Pavement Density Test Track Modified AC Test Track Unmodified AC, R 2 = 0.29 Test Track Modified AC, R 2 = ESALs

16 What Factors Cause this Variability? Source DF P-Value Significant Lift Yes Binder Yes Aggregate Type Yes Gradation Yes NMAS Yes Error 177 NA NA Based on Analysis of Variance

17 NCHRP 9-9(1) 9 9(1) Field Projects Verification of N design Table

18 Experimental Plan Sample 40 pavements at the time of construction with a range of: Lift Thickness to NMAS (2-4) Design Gyration Level (50-125) Binder Grade (Normal to +2 bumps) Gradation (Fine or Coarse)

19 Experimental Plan Plant mix taken at time of construction, compacted to 100 and 160 gyrations in three SGCs: Baby Pine (AFG1A) Small Troxler (4141) Brovold/Test Quip Used in 2001 only Data not yet reduced

20 Experimental Plan Roadway cores taken at construction, 3 months, 6 months, 1 year and 2 years after construction from right wheel path Goal: predict gyrations to match field density

21 NCHRP 9-9 (1): Field Project Locations Legend : Project Site

22 General Observations Gradation, coarse or fine, was related to compaction level: Almost all 75 gyration mixes were fine graded Two-thirds of 100 gyration mixes were coarse graded All 125 gyration mixes were coarse graded Binder Grade Bumps: 15 of 17, 100 gyration mixes included at least one binder grade bump All 125 gyration mixes included at least a one grade bump

23 Cumulative Frequency, % Cumulative Frequency of Construction Densities 55% 78% Percent Maximum Density, %

24 Summary of Projects with Two Years of Traffic

25 Pavement Densification Normalized Frequency, Percent One Year, N=38 2 Year, N=14 One Year, N=14 Construction N= Density, Percent Theoretical Maximum

26 Design Vs Predicted Gyrations Predicted Gyrations to Match Field Density at 2 Years Brand 1 SGC Brand 2 SGC Line of Equality Linear (Brand 1 SGC) Linear (Brand 2 SGC) R 2 = R 2 = Design Gyrations

27 Design Gyrations Vs Two Year Traffic 160 Predicted Gyrations to Match Field Density R 2 = R 2 = Brand 1 SGC Brand 2 SGC Power (Brand 1 SGC) Power (Brand 2 SGC) ESALs

28 Comparison of Modified and Unmodified Sections After Two Years Predicted Gyrations to Match Field Density at Two Years Brand 1 Modified Brand 2 Modified Brand 1 Neat Brand 2 Neat ESALs

29 Comparison of Coarse and Fine 160 Mixes - Two Years Design Gyrations to Meet Density at Two Years R 2 = R 2 = Brand 1 Coarse Brand 2 Coarse Brand 1 Fine Brand 2 Fine ESALs

30 Comparison of Nominal Maximum Aggregate Size Two Years Predicted Gyrations to Match Field Density at 2 Years Brand mm R 2 = 0.81 Brand mm R 2 = 0.70 Brand mm R 2 = 0.32 Brand mm R 2 = mm NMAS Brand mm NMAS Brand mm NMAS Brand mm NMAS Brand E+06 2E+06 2E+06 3E+06 3E+06 4E+06 4E+06 5E+06 5E+06 ESALs

31 Comparison of Number of Gyrations to Match Field Density for Two Compactors y = x R2 = Brand 2 SGC Line of Equality Brand 1 angle = 1.24 Brand 2 angle = Brand 1 SGC

32 Summary of Two-Year Performance of NCHRP 9-9(1) 9 9(1) Projects Rutting generally non-existent. One project with approximately 0.25 inch Minor ravelling common Several overlays over PCC evidence reflective cracking, even when total (new) overlay 3.5 inches or more Joints vary from fair to very good Some permeability evidenced by wet spots

33 Summary Test Track Data Indicates: Modified binders densify less than unmodified binders This may mean that mixes containing modified binders maybe designed at lower gyrations or higher asphalt contents to enhance durability Aggregate type, binder grade, nominal maximum aggregate size and gradation all affect predicted Ndesign values

34 Summary - Continued Data from Test Track and NCHRP seem to confirm current compaction level 0.3 to 3 million ESALs Results indicate that different compactors provide different compactive efforts Scatter in 9-9(1) 9 9(1) data decreases with additional traffic Trends developing, should be well founded once 2-year 2 core data collected

35 Thank You! Acknowledgements The Authors thank the National Cooperative Highway Research Program for their support of NCHRP 9-9 9(1), the U.S. state pooled fund participants and FHWA for their support of the NCAT Test Track