Effect of Diamond Grinding on Noise Characteristics of Concrete Pavements in California

Effect of Diamond Grinding on Noise Characteristics of
Concrete Pavements in California
Shubham Rawool1 and Richard Stubstad2
ABSTRACT
The construction of sound walls along highways has been the primary noise mitigation strategy
in California and in many other western States. Sound walls cost approximately $1.5 million
per mile and are effective only in close proximity to the highway, on the “far” side of the sound
wall, so to speak.
In its efforts to explore other noise mitigation strategies, the California Department of Trans-
portation (Caltrans) recently conducted a study to determine the effect of diamond grinding on
the noise characteristics of existing concrete pavements. Since the noise generated at the tire–
pavement interface is the greatest contributor to highway noise, quieter pavement surfaces can
reduce overall noise levels for both road users and neighborhoods—whether sound walls are
used or not.
On-board sound intensity (OBSI) measurements were conducted on six routes in California, for
a total of 42 evaluation sections; each evaluation section was 440 ft (136.8 m) long. OBSI
measurements before and after diamond grinding were recorded. Following are the overall con-
clusions that were reached after the pre- and post-grinding OBSI levels were measured:
• There is a significant and readily audible reduction in OBSI levels (and hence in tire–
pavement noise) after grinding.
• An average 2.7 dBA reduction in OBSI levels was observed for all test sites.
• Among the six routes, the highest average reduction of 4.4 dBA was observed on I-5
near Richards Boulevard in Sacramento County, and the lowest reduction of 1.2 dBA
was observed on State Route 60 (on a single test section) in San Bernardino County.
• The highest reductions in sound intensity levels on a 1/3-octave band basis occurred in
the 1600 Hz band, while the lowest reductions occurred in the 1000 Hz bandwidth.
INTRODUCTION
The construction of sound walls along highways has been the primary noise mitigation strategy
in California and many other States. Since the sound walls have their own limitations, other
strategies which could be used in conjunction with the sound walls are investigated. Among the
strategies that can reduce noise levels and sustain them while maintaining durability, maintain-

1 Shubham Rawool, Applied Research Associates, Inc., 1111 Howe Avenue, Suite 540, Sacramento, CA 95825;
email: srawool@ara.com; phone: 916-920-9850.
2 Richard Stubstad, Applied Research Associates, Inc.; email: rstubstad@ara.com; phone: 916-920-9850
Effect of Diamond Grinding on Noise Characteristics
235

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ability, and friction is improving pavement surface characteristics during construction or dia-
mond grinding the concrete surface post-construction. Efforts are underway to determine the
optimum surface characteristics that would simultaneously address tire pavement noise, texture,
smoothness, and friction.
In its effort to develop newer noise mitigation strategies, the California Department of Trans-
portation (Caltrans) is evaluating various alternatives that can reduce highway noise, even in
existing portland cement concrete pavement (PCCP). Since the noise generated at the tire–
pavement interface is the greatest contributor to highway noise, quieter pavement surfaces can
reduce the overall noise levels substantially for road users and neighborhoods alike. The noise-
reducing capabilities of open-graded asphaltic mixtures, porous concrete, and diamond-ground
pavement surfaces are some of the alternative approaches that are being considered to reduce
tire–pavement interface noise.
Grinding on bridge decks and elevated structures has been found to reduce tire–pavement
source levels by 3 to 10 “average weighted decibels” (dBAs), with relatively comparable reduc-
tions in wayside noise measurements (Ref. 1). Also, in Arizona, diamond grinding of trans-
versely tined concrete surfaces has been found to reduce pavement interface source levels by up
to 9 dBAs (Ref. 1). Similar results were also obtained in a study conducted on Route 101 in
California. Average noise-level measurements and single-vehicle pass-by (not pavement inter-
face) values were used to determine the reduction in noise levels after diamond grinding. Al-
though the results of the average noise levels were found to be inconclusive, the results of the
pass-by noise-level measurements showed an average noise drop of approximately 6 dB at 25 ft
and 4 dB at 50 ft (Ref. 2). Considering this potential level of noise reduction, it can be con-
cluded that diamond grinding of concrete surfaces may be a feasible means of reducing noise
levels on existing PCCP.
Objective of the Study
The main objective of the Caltrans study was to determine the effect of diamond grinding on
the tire–pavement noise characteristics of PCCP. Existing tire–pavement noise characteristics
of in-service pavements were determined both before and after grinding. The study had the
following specific objectives:
• Conduct on-board sound intensity (OBSI) measurements to determine tire–pavement
noise levels on PCCP sections before and after diamond grinding.
• Compare these before-and-after OBSI results to determine the change in sound intensity
(SI) levels after grinding.
• Select candidate PCCP sections to monitor long-term noise characteristics.
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Figure 1. OBSI equipment setup.
DATA COLLECTION
OBSI Equipment
The OBSI method was used to measure tire–pavement interface noise. The equipment setup
used to conduct measurements consisted of a Bruel and Kjaer front-end analyzer and the asso-
ciated “Pulse” software package, two probes (each consisting of a microphone pair), a mount-
ing fixture, and a Michelin Standard Reference Test Tire (SRTT—see Figure 1).
Each probe has two 0.5 in. (13 mm) diameter, phase-matched condenser microphones spaced
0.625 in. (16 mm) apart and fitted with a wind screen (Figure 2).

Figure 2. Schematic diagram depicting the microphone setup.
The two probes are placed 3 in. (76 mm) above the pavement and 4 in. (102 mm) away from
the tire sidewall and are positioned to capture SI at the leading and trailing edges of the tire
contact patch (Figure 2). The SI at the two probes is captured simultaneously by the front ana-
lyzer in real time and can be viewed on an onboard computer using the Pulse software. The
intensity values at the leading and trailing edges of the tire contact area are averaged together
on an energy basis to determine the SI for a given pavement section.
Effect of Diamond Grinding on Noise Characteristics
237

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Testing Procedure
The test vehicle was driven at a constant speed using the cruise control. For each route, test
sections with minimum grade and alignment changes were selected. Tests were conducted at
times when traffic was sparse and on days when dry pavement and favorable wind conditions
were present. To limit the data to as few variables as possible, a test plan with the following
parameters was developed:
• Constant speed of 60 ± 2 mi/h (97 ± km/h).
• Michelin Standard Reference Test Tire (SRTT).
• Cold tire pressure 30 lbf/in2 (206.8 kPa).
• No significant grade.
• Dry pavement.
To reduce any bias caused by the equipment; microphones, preamplifiers, and cords were num-
bered and placed in the same location for each test. Before and after every test, each of the four
microphones was calibrated.
Test Sections
All pavement sections considered for this project are listed in Table 1. Caltrans originally iden-
tified 15 routes on which pre-grind OBSI measurements were conducted. A total of 81 evalua-
tion sections, each of 5-second duration (440 ft [134 m]), were measured using the OBSI test-
ing equipment.
Since some of the pavements remained unground by the time this study ended, only 6 of the
original 15 routes (consisting of several test sections on each route) could be tested for post-
grind noise levels. However, these included over half (42 out of 81) of the evaluation sections
originally surveyed in the pre-grind phase of the project. All the evaluation sections except one
(along 1-60 southbound) showed a reduction in SI after grinding. The section on SR 60 begin-
ning at postmile (PM) 7.9 was excluded from analysis because it was not considered typical.
Table 2 and Figure 3 show pre- and post-grind SI values for the six routes. There was a reduc-
tion in SI on all the routes after grinding. The greatest reduction in SI value—4.4 dBA—was
observed on I-5 in Sacramento County, and the lowest reduction (1.2 dBA) was observed on
State Route 60 in San Bernardino County. On average, the reduction for all six sites was
2.7 dBA—a significant and audibly noticeable improvement.

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Table 1
Details of Tested Routes
No. of
Tested
Date of
Site
Starting
Ending
Sections
Pre-grind
Date of Post-
No. Route
County
Postmile
Postmile
(440 ft)
Testing
grind Testing
1 I-5
LA 32.3 44.3 7
5/22/2007
Not
ground
2 I-10
LA 18.3 32.7 7
5/22/2007
Not
ground
3 SR-60 LA 23.9 30.4 3
5/8/2007
Not
ground
4 SR-60 SBD 0 9.9
2
5/8/2007
6/4/2008
5 I-15 SBD 0 3.8
4
5/9/2007
Not
ground
6 I-15 RIV
51.4 52.3 2
5/9/2007
Not
ground
7 I-10 RIV 0 8.2
4
5/9/2007
Not
ground
8 I-15 RIV 8.1 23.9 6
5/23/2007
6/5/2008
9 SR-91 RIV 0 9.0
4
5/10/2007
Not
ground
10 I-5
ORA 14.5 21.3
4
5/23/2007
6/5/2008
11 I-405 ORA 16.9 24.2
3
5/22/2007
6/5/2008
12 SR-101 SFO 0
4.2
1
5/06/2007
Not
ground
13 I-280 SCL 5.1 7.8
4
5/06/2007
Not
ground
14 I-5
KER 10.2 15.8
14
4/16/2008
5/17/2008
15 I-5
SAC 24.1 24.8
16
5/19/2008
7/24/2008

Table 2
Pre- and Post-grind SI Values From All Six Routes
After Grind
Route
Pre-Grind SI
Post-Grind
Reduction
Site No.
Name County
(dBA)
SI (dBA)
(dBA)
1 SR-60
SBD 105.1 103.9 1.2
2 I-15 RIV 103.9 101.8 2.1
3 I-5 ORA
104.0 101.3 2.6
4 I-405
ORA
104.4 102.0 2.5
5 I-5 KER 103.2 100.0 3.2
6 I-5 SAC 104.7 100.3 4.4
Average 104.2
101.5
2.7

Effect of Diamond Grinding on Noise Characteristics
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106.0
) 105.0
A
B
d 104.0
(
i
t
y
103.0
ns
t
e 102.0
n
101.0
ound I
S 100.0
99.0
SR-60
I-15
I-5
I-405
I-5
I-5
Average
Routes
Pre-Grind
Post-Grind

Figure 3. Pre- and post-grind SI values for all six routes.


Detailed Data Analysis for I-5 in Kern County
A detailed analysis was conducted on the I-5 project in Kern County. This site was chosen for
detailed analysis since it had the most evaluation sections among all sites tested. Also, the data on
this site were considered to be most representative to study the detailed effect of grinding on SI
levels because pre- and post-grind data were collected within a 1-month period of one another.
On this route, data were collected in both the northbound and southbound directions. In the
northbound direction, five consecutive 440-ft (134-m) sections starting at PM 11.8 were meas-
ured. Similarly, in the southbound direction, nine consecutive 440-ft (134-m) sections starting
at PM 12.3 were measured.
SI Levels for I-5 in Kern County
A comparison of the pre- and post-grind SI levels is shown in Figure 4 and Figure 5 for the
southbound and northbound directions of traffic, respectively. The average pre-grind noise
level in the southbound direction was 102.8 dBA, whereas in the northbound direction it was
104.0 dBA. Correspondingly, the average post-grind noise levels were 100.1 dBA and 100.0
dBA in the southbound and northbound directions, respectively.
Note that the average pre-grind noise level was approximately 1 dBA higher in the northbound
direction compared to southbound direction. After grinding, a reduction of 3.9 dBA northbound
and 2.9 dBA southbound was observed (Figure 6). The average post-grind SI level for this site
was 100 dBA. This means that the results in terms after-grind dBA were similar, regardless of
the initial noise level.
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240

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I-5 Kern County - Southbound
104
) 103
A
B
d 102
t
y (
101
nsi
t
e 100
n
99
98
Sound I
97
Sect 1
Sect 2
Sect 3
Sect 4
Sect 5
Sect 6
Sect 7
Sect 8
Sect 9 Average
Distance (ft)
Pre-Grind
Post-Grind

Figure 4. A-weighted SI levels averaged over four runs for southbound I-5 in Kern County.

I-5 Kern County - Northbound
105
) 104
A
B 103
d
t
y ( 102
nsi 101
t
e
n 100
99
Sound I
98
97
Sect 1
Sect 2
Sect 3
Sect 4
Sect 5
Average
Distance (ft)
Pre-Grind
Post-Grind
Figure 5. A-weighted SI levels averaged over four runs for northbound I-5 in Kern County.

Effect of Diamond Grinding on Noise Characteristics
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Reduction in SI Levels After Grinding
5
)
A
B 4
d
t
y ( 3
nsi
t
e 2
n
1
Sound I
0
Sect 1
Sect 2
Sect 3
Sect 4
Sect 5
Sect 6
Sect 7
Sect 8
Sect 9 Average
Distance (ft)
I-5 NB
I-5 SB
Figure 6. Reduction in noise levels after grinding on I-5 in Kern County.

1/3-Octave Analyses for I-5 in Kern County
One-third-octave band analyses of SI levels were also conducted to determine the consistency
among runs and delineate the effect of grinding on the individual 1/3-octave bands.
Southbound Direction: Figure 7 and Figure 8 show pre- and post-grind center frequency
bands from 500 Hz to 5000 Hz for all four runs on southbound I-5. In the figure, each run (Rx)
is represented by three SI curves, the first curve for the microphone at the trailing edge (Tr) of
the tire, the second for the microphone placed at the leading edge (Ld), and the third represent-
ing the average for the leading and trailing edge microphones. As shown in these figures, the
consistency of SI values among runs is very clear in the 1/3-octave band analysis.
Pre- and post-grind SI values at 1/3-octave bands were compared to determine the effect of
grinding on the various individual octave bands. Table 3 and Figure 9 show pre- and post-grind
1/3-octave band spectra comparisons for the southbound direction. The greatest reductions for
the 1/3-octave bands occurred in the 1600 Hz band, while the lowest reduction was for bands
between 500 and 1000 Hz. However, all octave bands showed significant reduction levels
within audible frequencies.
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Pre grind 1/3 Octav e Spe ctra for all runs and microphone position for I-5 SB
R1-Tr
R1-Ld
100.0
R1-Avg
)
R2-Tr
A
95.0
B
R2-Ld
d
(
90.0
R2-Avg
i
t
y
ns
R3-Tr
85.0
t
e
n
R3-Ld
80.0
R3-Avg
ound I
75.0
R4-Tr
S
R4-Ld
70.0
R4-Avg
500
630
800
1000
Runs with le ading and
1250
1600
2000
500
trailing microphone
2
150
00
0
3
40
positions
500
Ce nte r Freque ncy band (Hz)
Figure 7. Pre-grind 1/3-octave band spectra for Southbound I-5 in Kern County.


Post grind 1/3 Octav e Spe ctra for all runs and microphone position for I-5 SB
R1-Tr
R1-Ld
R1-Avg
100.0
)
R2-Tr
A
95.0
B
R2-Ld
d
(
90.0
R2-Avg
i
t
y
s
R3-Tr
n
85.0
t
e
R3-Ld
n
80.0
R3-Avg
75.0
R4-Tr
ound I
S
R4-Ld
70.0
R4-Avg
500
630
800
1000
Runs with le ading and
1250
1600
2000
trailing microphone
2500
3150
4000
positions
5000
Ce nte r Fre que ncy band (Hz)
Figure 8. Post-grind 1/3-octave band spectra for Southbound I-5 in Kern County.
Effect of Diamond Grinding on Noise Characteristics
243

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Table 3
SI Values for Various Center Frequency Bands on
Southbound I-5 in Kern County
Center
Frequency Band
Pre-Grind SI
Post-Grind SI
Difference in SI
(Hz)
(dBA)
(dBA)
(dBA)
500 86.2 84.4 1.8
630 91.2 89.0 2.1
800 96.7 94.6 2.1
1000 96.6 94.8 1.8
1250 94.5 92.1 2.4
1600 94.9 88.3 6.6
2000 91.2 86.4 4.8
2500 87.1 83.2 4.0
3150 83.7 78.5 5.3
4000 80.8 75.4 5.4
5000 77.9 72.3 5.6


1/3 Octave Band Spectra for I-5 SB
100.0
)
A
95.0
B
(
d
90.0
t
y
nsi
85.0
t
e
n
80.0
d I
75.0
Soun
70.0
500
630
800
1000
1250
1600
2000
2500
3150
4000
5000
Center Frequency Bands (Hz)
Pre-Grind
Post-Grind
Figure 9. Pre- and post-grind 1/3-octave band spectra for northbound I-5 in Kern County.
Rawool and Stubstad

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Document Outline

• Introduction
• Data Collection
• Conclusions and Recommendations
• References

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