1. Office of Materials and Road Research
Asphalt Compaction Evaluation using Rolling Density Meter (TH 52 and TH14 Field Trials) Dr. Shongtao Dai, MnDOT Dr. Kyle Hoegh, MnDOT Dr. Lev Khazanovich, U. of Pittsburgh NRRA Pavement Conference (May 24, 2017)
Mn/DOT
Office of Materials and Road Research

2. Rolling Density Meter (RDM)
RDM: A GPR device.
One channel or multi-channels
Specific designed to measure HMA compaction density
SHRP2 R06C Research Product (2013)
Dielectric values related to air voids.
Rolling Density
Meter (RDM)

3. SHRP2 R06C Implementation (2015)
Objective:
Evaluate RDM equipment.
Provide support to states to assist to implement RDM.
Partnership
FHWA, AASHTO, CH2M Hill
University of Minnesota
MnDOT
Maine DOT
Nebraska DOT
Field Trails
Maine: HWY 9 near Clifton
Nebraska: HWY2, Lincoln
Minnesota: TH.14 and TH.52

4. Benefits Pavement density has great effects on performance.
Lack of density --- localized failure
1989 – “Effect of Compaction on Asphalt Concrete Performance” (Wash.DOT)
Each 1% increase in air voids (over 7 percent)
tends to produce ~10 percent loss in pavement life.
Core used to determine density
At a particular location, does not represent the entire
pavement density
Need a way to obtain full coverage of the surface
GPR is a good tool: Continuous profile

5. Principal
Wave propagation in solids
Provides full coverage

6. Questions
Measurement difference among the antenna pairs?

7. Underlying layer effect on surface measurement?
How thick does the HMA layer need to be so that the underlying layer (agg. base) has no effects?
Surface layer dT
Underlying layer
h1 =v* t1 /2
v= c/1
dT ~ 0.439us

8. Fr ~ 0.5 v (tr/fc)1/2 Footprint area of an antenna (Fresnel Zone)?
at D=18”, Fr (Radius) ~ 6” (for 1.5Ghz)
D=12”, Fr (Radius) ~ 3.8” (for 2.5Ghz-RDM)

9. Field Testing and Assessment Method
Selected MN TH52 (D6) and TH14 (D6)
7 miles on TH52 and 11 miles on TH14
Objectives:
Develop methods to assess compaction uniformity and quality
Make recommendation for feasibility of implementation.
i.e. when it can and can’t be used
Gathering data necessary for specification development.

10. MN Project #1 (Summer 2016) TH52 (D6): ~7 miles
M&O: Mill 1.5” and overlay 2x1.5”
4 Test Sections (FHWA/AASHTO funding)
No added binder + 4 rollers (control)
Added binder (+0.5%) + 4 rollers
No added binder + 5 rollers
Added binder (+0.5%) + 5 roller
The entire 7 mile project was scanned
30 scans per foot
3 antenna measurements per pass
Core calibrations along the entire project were used to develop a model relating RDM measurements to air void measurements
1.5”
1.5”
3” Exist

11. MN Project #2 (Summer 2016) TH14 (D6): 14 miles
M&O: Mill 2” and overlay 2” and1.5”
6 Test Sections:
¾” mix + 3 rollers (control)
¾” mix + 4 rollers
½” mix + 3 & 4 rollers
½” mix (Evotherm) + 3 rollers
¾” mix (Evotherm) + 3 rollers
Scanned 11 Miles on Top lift
30 scans per foot
3 antenna measurements per pass
Core calibrations along the entire project were used to develop a model relating RDM measurements to air void measurements
1.5” 2”
4-5” Exist

12. Results On-Site Identification of high and low levels of compaction
Mainline Survey: multiple passes
On-Site Identification of high and low levels of compaction
Joint Survey: one antenna close to joint

13. TH14 TH52 Relating Dielectric Measurements to Air Void Content
32 cores from TH52
31 cores from TH14
TH14
TH52

14. Similar relationships on Nebraska and Maine projects Nebraska HWY 2
July 19, 2016
1.25 in” overlay
1000 ft surveyed
Collected eight cores
Maine HWY 9
July 13, 2016
1500 ft surveyed
Collected five cores

15. Histogram Use histogram to assess uniformity and quality.
All Data Collected
Sampling Rate = 0.4 in/scan.
> 26 million measurements
Analysis based on 4 in. moving average
Equivalent to >1 million cores
Summary Stats
93.2% median density
STD: 1.18
97.5% locations
density> 90.8%

16. TH 52 – Mainline Number of Roller Effects
Section with added binder+5 rollers has highest density
Median Density:
Blue: 93.4%
Yellow: 93.1%
Green: 93%
Red: 94%

17. TH 52 – Longitudinal Joint
Top lift Mainline vs Confined and Unconfined Joints Summary:
93.5% (ML), 92.6%(CJ) and 91.4%(UCJ)
SD: 0.94(ML); 1.22(CJ); 1.8(UCJ)
Density:
UCJ/ML=97.7%; CJ/ML=99%
Core data: UCJ/ML=95.1%
CJ/ML = 99.1%
97.5% locations:
> 91.6%(ML),
> 90.2% (CJ)
> 87.8% (UCJ)

18. TH 52:Comparison with other Factors
Import RDM data into Veta for comparison with IR and other data

19. TH 14 – Mainline Comparison of Test Sections
Mix B (3/4-) to A(1/2-): not much difference on compaction.
Adding a roller: density slightly increased on this project. .
Median Density:
Blue: 94.1%
Red: 94.2%
Yellow: 93.5%
Green: 93.3%

20. TH 14 – Longitudinal Joint
Evotherm helped on the joint compaction density
Median Density:
Red: 93.1% (ML)
Blue: 93.1% (ML)
Yellow: 92.9%(CJ+Ev)
Green: 91.5% (CJ)
(CJ+Ev)/ML=99.7%
Core:
93.8%(ML)
93.5%(CJ+Ev)- only 2 cores
CJ/ML= 99.6%

21. Implementation Recommendations for Acceptance
Recommendation #1 - Mainline:
Require dielectric distribution readings from RDM per 500ft.
Ex: Require E of 5.31 >= 92% density?
E of 5.31 includes > 95% data
Take cores at E=5.31, Then measure density

22. Recommendation #2 – Longitudinal Joint:
Require RDM readings at the longitudinal Joint and X distance away from the Joint, use ratio of dielectrics between LJ and ML.
(No cores required)
Ex: Ratio of E >= 95%

23. MnDOT’s Plan 2017 Field Testing Objective:
2 to 3 construction projects in 2017 will be selected for more data collection. A consultant will be hired for part of the data collection. The focus will be placed on:
1) Educating consultant and contractors on this new technology
2) Further verifying the developed statistical method.
3) Testing application feasibility of vehicle mounted RDM system on
construction projects;
If all things go well, a few projects will
require the device in 2018

24. Summary
RDM is a good tool for mapping a continuous coverage of the relative compaction levels (higher dielectric = higher compaction)
Histograms and general statistics can be used to give a complete assessments of the in-place compaction
Potential Uses:
Assess compaction density and uniformity for QC/QA.
Provide on-site feedback to contractor of high and low compaction locations that they can cross-check with differences in mix or paving strategies in those locations to determine optimal construction procedures
Identification of trends in the air void content maps that can be cross-checked with IC and other data to determine the most critical factors in achieving higher density

25. Acknowledgements FHWA/AASHTO for providing RDM
MnDOT district materials and constructions
UMN students
Nebraska and Maine DOTs

26. Thank you!