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Asphalt Compaction Evaluation using GPR:TH 52 and TH 14 Field Trial
Dr. Kyle Hoegh, MnDOTDr. Shongtao Dai, MnDOT
Mn/DOTOffice of Materials and Road Research
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 potential tool: Continuous profile Locate relative high or low density areas based on
dielectric map
Why?
Data Collection Video3D Radar and Rolling Density
Meter
Equipment
Wave propagation in solids
Provides full coverage
Principal
Summer Testing Objectives Selected TH52 (D6) and TH14 (D6)Validate calibration methodology on large scale
pavements.Make recommendation for feasibility of
implementation. i.e. when it can and can’t be used Assess repeatability of the method
Gathering data necessary for specification development.
Project #1 (Summer 2016) TH52 (D6):
~7 miles M&O: Mill 1.5” and overlay 2x1.5” 4 Test Sections (FHWA funding)
No added binder + 4 rollers (control) Added binder (+0.3%) + 4 rollers No added binder + 5 rollers Added binder (+0.3%) + 5 roller
The entire 7 mile project was scanned 30 scans per foot (10 scan-4 in. moving average used in analysis) 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
TH14 (D6): 14 miles M&O: Mill 2” and overlay 2” and1.5” 4 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 (10 scan-4 in. moving average used in analysis) 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
Project #2 (Summer 2016)
General Process On-Site Identification of
high and low levels of compaction
TH14
CurrentMnDOTRDM
Relating Dielectric Measurements to Air Void Content
y = 15.652e-1.013x
R² = 0.6887
0.0%
2.0%
4.0%
6.0%
8.0%
10.0%
12.0%
14.0%
16.0%
4.50 4.70 4.90 5.10 5.30 5.50 5.70 5.90
Core
Mea
sure
d Ai
r Voi
ds
RDM Measured Dielectric
TH52
Relating Dielectric Measurements to Air Void Content
3D Radar
UMN MN RDM
UMNMaine RDM
UMN Nebraska RDM
Uncertainty in Core Measured Air Voids
Hall, K. D., F. T. Griffith, and S. G. Williams. TRB Record No. 9 1761, pp. 81‐85.
Highway 52 Findings - Histogram 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
6.78% Median Air Voids 97.5% locations
less than 9%air voids
TH 52 – All Test Sections RDM RDM Comparison of Test Sections
Section with added binder+5 rollers has highest density
Control (4R+No Added Binder)5 R on No Added Binder
4 R on Added Binder
5R on Added Binder
TH 52 – All Test Sections Cores Comparison of Test Sections
Section with added binder+5 rollers has highest density in both cores and RDM measurements
Insignificant differences otherwiseControl (4R+No Added Binder) 5 R on No Added Binder 4 R on Added Binder 5R on Added Binder
Bot
h La
nes
mean 5.97 6.31 6.5 5.895% CI 0.56 0.74 0.86 1.66STD 0.95 1.07 0.98 1.6997.5th % 7.83 8.42 8.42 9.112.5th % 4.12 4.21 4.58 2.49n Data 11 8 5 4
TH 52 -Sorted Histograms Top lift Mainline Left
and Right Lane Summary: 6.4% (R) and 6.6%
(L)air voids respectivelyDensity:
Right: 93.6% Left: 93.4%
STD: 1% and 0.9% 97.5% locations
below 8.4%air voids forboth lanes
Blue – Right Lane (4’-8’)Red – Left Lane (4’-8’)
TH 52 -Sorted Histograms Top lift Joint Unconfined
and Confined Summary: 8.69%(UCJ) and 7.29%(CJ)
air voids, respectivelyDensity:
UCJ: 91.3%; CJ:92.7%; R = 98.5%
STD: 1.8% (UCJ) and 1.2%(CJ)
97.5% locations below 11.99%(UCJ) and 10.2%(CJ) air voids, respectively
Blue – Conf. J (3” offset)Red – Unconf. J (3” offset)
TH 52 -Sorted Histograms Top lift Mainline and
Confined Joint Summary: 6.59% (ML) and 7.29%(CJ)
air voids, respectivelyDensity:
CJ=92.7%; ML=93.4%; R=99.3%
97.5% locations below 8.37% and 9.69% air voids, respectively
Blue – Conf. J (3” offset)Red – Mainline
TH 52 -Sorted Histograms Top lift Mainline vs Confined and
Unconfined Joints Summary: 6.59% (ML), 7.29%(CJ) and
8.69(UCJ) air voids, respectively Density:
CJ=92.7%; UCJ=91.3%; ML=93.4%
UCJ/ML=97.7% (ML-UCJ=2.1%); CJ/ML=99.3% (ML-CJ=0.7%)
97.5% locations below 8.11%(ML), 9.89%(CJ) and 10.7(UCJ) air voids, respectively
Blue – Conf. JRed – MainlineYellow – Unconf. J
TH 52 -Sorted PlotsBreak data down by location
TH 52:Comparison with other FactorsImport RDM data into Veta for comparison with IC and other data
9.72 9.725 9.73 9.735 9.74 9.745 9.75 9.755 9.76x 104
3
3.5
4
4.5
5
5.5
6
6.5
7
Stationing [ft]
Die
lect
ric [
]
Local Increase after Added Roller
Local decreases (blue) at unconfined edges
dielectric
[A] [B] [C]
TH 52 – Experimental Design Results in Left Lane MainlineNo Significant difference in control mix from 4 rollers (red) to 5
rollers (blue), except initial jump
TH 52 – Comparison with other Factors
Import RDM data into Veta for comparison with IC and other data
9.72 9.725 9.73 9.735 9.74 9.745 9.75 9.755 9.76x 104
3
3.5
4
4.5
5
5.5
6
6.5
7
Stationing [ft]
Die
lect
ric [
]
Local Increase after Added Roller
Local decreases (blue) at unconfined edges
dielectric
1070+50 1071+00 1071+50 1072+00 1072+50 1073+00 1073+50 1074+00 1074+50
-7.5-6.25
-5.0-3.75
3D Radar Relative Compaction (3 in. X 3 in. spacing)
Rolling Density Meter Relative Compaction (2 ft. Spacing)
• 3D Radar can provide better coverage and precision at a tighter spacing. However RDM has advantages too:
• Less Expensive• Requires less user expertise (ex. Antenna
Correction)• RDM is easier to operate close to joints
when adjacent lanes are open to traffic• Real time results (easier for providing on-
site feedback)
Lower Compaction Higher Compaction
GPR: Asphalt Relative Compaction Assessment
TH 14 – All Test Sections Comparison of Test Sections
Adding a roller: compaction density increase on this project. Adding Evotherm: not much difference on compaction. Mix B (3/4-) to A(1/2-): not much difference on compaction.
Red – ¾”mix + 3 rollers [Control (4’-8’)]
Green - ¾” mix (Ev) + 3 rollers
Yellow - ½” mix + 3 rollers
Blue – ¾” mix + 4 rollers
Red – ¾”mix+ 3 rollers [Control (4’-8’)]
Green – ½” mix (Ev) + 3 rollers
Yellow - ½” mix + 4 rollers
Blue – ¾” mix + 4 rollers
TH 14 – All Test Sections Comparison of Test Sections (Core data)
TH 14 – All Test Sections
Percent within limits (PWL) implications Good measure if enough data: takes into account magnitude and
spread in data < 10 data points for each QA Core assessment:
Core PWL st.dev > 10 percent
>150,000 data points for each RDM assessment
http://www.fhwa.dot.gov/publications/research/infrastructure/pavements/pccp/04046/04046.pdf
FHWA-HRT-04-046 Evaluation of Procedures for Quality Assurance Specifications
TH 14 -Sorted Histograms 3 Roller on ¾” Mix:
Confined Joint and Mainline.
Blue: Conf J. side(3”offset)
Red: Mainline 4-8’
Summary Stats 5.23 (ML) and
5.06(CJ) dielectric, respectively
STD: 0.11 and 0.11, respectively
3.6% higher dielectric in mainline CJ/ML=96.7%
TH 14 -Sorted Histograms
Blue: conf.J (3”offset)
Red: Mainline (4’to8’)
Summary Stats 5.22 (ML) and
5.20(CJ) dielectric, respectively
STD: 0.10 and 0.09, respectively
0.4% higher dielectric in mainline CJ/ML=99.6%
3 Roller on ¾”mix( Evotherm):Confined Joint and Mainline.
TH 14 -Sorted Histograms4 Roller on ¾” Mix: Confined Joint and Mainline.
Blue: Conf.J side(3”offset)
Red: Mainline 4-8’
Summary Stats 5.40 (ML) and
5.29(CJ) dielectric, respectively
STD: 0.10 and 0.12, respectively
2.1% higher dielectric in mainline CL/ML=97.9%
TH 14 -Sorted Histograms
Blue: Conf.J (3”offset)
4 Roller on ½” Mix:Confined Joint and Mainline.
Red: Mainline 4-8’
Summary Stats 5.38 (ML) and 5.35
(CJ) dielectric, respectively
STD: 0.09 and 0.09, respectively
0.6% higher dielectric in mainline CJ/ML=99.4%
Implementation Recommendations:
Longitudinal Joint (RDM)
Recommendation #1 - LJ: Require dielectric distribution readings from RDM per 500ft.
Ex: Require E of 5.31 >= 90% density? E of 5.31 includes > 95% data Take cores at E=5.31, Then measure density
0.0%
0.5%
1.0%
1.5%
2.0%
2.5%
3.0%
3.5%
4.0%
4.9
95
.03
5.0
75
.11
5.1
55
.19
5.2
35
.27
5.3
15
.35
5.3
95
.43
5.4
75
.51
5.5
55
.59
5.6
35
.67
5.7
15
.75
5.7
95
.83
5.8
75
.91
5.9
5
% o
f to
tal m
ea
sure
me
nts
in e
ach
dat
ase
t
Dielectric
Recommendation #2 - LJ: Require RDM readings at the logitudinal Joint and X distance away from the Joint, use % difference of dielectric. (No cores required)
Ex: Require Joint E >= 92% of mainline E ?
4
4.5
5
5.5
6
6.5
0 20 40 60 80 100 120
Relat
ive Pe
rmitt
ivity,
e
distance, ft
S5 -3.0 ft EB
S5 -3.0 ft EB
S5 -1.0 ft EB (unconfined)
S5 -1.0 ft EB (unconfined)
Core Location
-0.5%
0.0%
0.5%
1.0%
1.5%
2.0%
2.5%
3.0%
3.5%
4.8 5 5.2 5.4 5.6 5.8 6 6.2
S5 -1.0 ft EB
S5 -3.0 ft EB
Unconfined Joint Median
3 ft from Joint Median
dEJoint 3' away (mainline)
91.45% different
Implementation Recommendations:
Mainline – 3D GPR
Recommendation #3A - M(3DGPR)Survey the whole project surfaceRequire dielectric distribution from 3DGPR every 500ft.Example A: Require E of 5.2 = 92% density?
E of 5.2 includes > 95% datatake cores at E=5.2, then measure density
Surface Arrival Amplitude
Longitudinal Distance from Starting Point, feet
Tru
ck L
ane
<--
----
----
--->
Cen
ter
Lane
Tra
nsve
rse
Dis
tanc
e fr
om th
e Lo
ngitu
dina
l Joi
nt, f
eet Dielectric Map
47 94 141 188 235 282 329 376
-2.25
-1.75
-1.25
-0.75
-0.25
0.25
0.75
1.25
1.75
2.25 4
4.2
4.4
4.6
4.8
5
5.2
5.4
5.6
5.8
6
DielectricConstant
Recommendation #3B - Mainline(3DGPR):Require a test strip to establish the dielectric histogramand establish E and density relationshipExample B: E of 5.2 = 92% density
E of 5.2 includes > 95% datatake cores at E=5.2, then measure density
Require to construct test strip where material changesThen use established histogram for project acceptance: dielectric
distribution on mainline should be similar. 95% data should > 5.2. (No cores required) No OK
Summary GPR can provide 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 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