noise reduction capacity of a composite pavement system
TRANSCRIPT
KSCE Journal of Civil Engineering (0000) 00(0):1-8
Copyright ⓒ2014 Korean Society of Civil Engineers
DOI 10.1007/s12205-014-0594-z
− 1 −
pISSN 1226-7988, eISSN 1976-3808
www.springer.com/12205
Highway Engineering
Noise Reduction Capacity of a Composite Pavement System
Seong-Kyum Kim*, Woo-Jin Park**, and Kwan-Ho Lee***
Received November 27, 2012/Revised 1st: June 21, 2013, 2nd: August 20, 2013/Accepted September 24, 2013/Published Online May 20, 2014
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Abstract
Rapid economic development has induced massive road construction, due to increased traffic and travel speeds. However, thisdevelopment has produced numerous social problems, such as air pollution, traffic noise and road vibration. By applying the theoryof Helmholtz resonators to asphalt pavement, special concrete blocks in the base course of asphalt pavement can be used to alleviatevarious types of traffic noise, such as noise produced by vehicle engines and tire. This research examines two laboratory tests on thesound absorption effect of concrete block and base concrete block, and their applicability in the construction of quiet pavements. Thenoise reduction effects of the specimens, which are constructed with a fixed size, space, and depth for each hole, are analyzed usingdifferent vehicle noise levels. Based on the test results for vehicle noise volume, measurement distance, and form and size of the holein which the base concrete block is placed, the use of special concrete base and quiet asphalt surface was determined to be a goodalternative solution for traffic noise levels in the range of 4 dB to 9 dB. Noise reduction effects were separated into two parts:, adifferent Hot Mix Asphalt (HMA) on the same base concrete block, and a different base block with the same HMA. HMA 3 on thesame base concrete block exhibited optimum noise reduction effects with measured noise reduction values in the range of 3 dB to6 dB. The measured noise reduction values of different base concretes, using the same HMA, ranged e dB to 4 dB. This result meansthat a quiet asphalt surface exhibited a greater noise reduction effect than a hole in the concrete base block. Based on the test results,the use of HMA 3 in Base D exhibited optimal performance.
Keywords: concrete base block, hot mix asphalt, quiet pavement, theory of the Helmholtz resonator, traffic noise
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1. Introduction
Noise pollution is an ever-increasing global problem. Although
numerous sources of noise exist, traffic noise is the main
contributor to environmental noise. Different sources of traffic
noise are prevalent; however, noise caused by the interaction
between tires and pavement is the most dominant component of
traffic noise within major city and the highway limits. One
approach to reduce tire-pavement noise involves improving the
material characteristics of the pavements such that it produces
less noise. The government has attempted to promote and
maintain quiet daily living and an educational environment. To
accomplish these objectives, the regulation of traffic noise is
necessary. The government is also actively involved in the
development of quiet paving materials and construction
technologies. One popular technology is the use of various types
of soundproofing along the side of the road to reduce traffic
noise. However, the installation of soundproofing significantly
inhibits the aesthetic attributes of the city.
The main purpose of this study is to develop a quiet pavement
system, to analyze the characterization of traffic noise and to
reduce traffic noise that is generated by the interaction between
tires and pavement. Based on the theory of Helmholtz resonators,
two concrete base blocks with different sizes of holes were
adopted. Four different types of asphalt pavements were adopted
for the surface course. Different combinations of base blocks and
asphalt pavement were constructed to achieve reduced traffic
noise.
2. Literature Review on Tire-pavement Noise
2.1 Sound Measurement Unit
Sound can be determined by two characteristics: frequency
and amplitude. Frequency is a measure of the number of
vibrations that occur in one second. Frequency, which is
measured in hertz (Hz), is also known as pitch. The wavelength
of any sound is the measurement of the shortest repetition length
for sound waves or the distance between rarefactions or between
compressions. The amplitude of a sound wave, which refers to
the loudness or sound pressure level, is measured in decibels
(dB). The decibel is a logarithmic scale that is based on the
logarithm of the ratio of the pressure to a reference pressure
TECHNICAL NOTE
*Member, Ph.D. Candidate, Dept. of Civil Engineering, Kongju National University, Cheonan 331-717, Korea (E-mail: [email protected])
**Ph.D. Student, Dept. of Civil Engineering, Kongju National University, Cheonan 331-717, Korea (E-mail: [email protected])
***Member, Professor, Dept. of Civil Engineering, Kongju National University, Cheonan 331-717, Korea (Corresponding Author, E-mail: kholee@kongju.
ac.kr)
Seong-Kyum Kim, Woo-Jin Park, and Kwan-Ho Lee
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(Leung, 2007). The decibel scale ranges from the threshold of
hearing, which consists of 0 dB, to the pain threshold, which
consists of approximately 140 dB. Table 1 lists the sound levels
for typical sources of noise, including various sources of
transportation noise (Sandberg, 1992).
2.2 Tire-Pavement Noise Generation Mechanism
The interaction between tires and pavement generates noise.
The noise level may vary significantly depending on the types of
the tire and pavement surface. Several mechanisms explain the
generation of sound at the interface between tires and pavement.
Certain factors contribute to the amplification of the
mechanisms. All mechanisms can be divided three categories:
air resonant mechanism, radial vibration mechanism and
adhesion mechanisms.
The air resonant mechanism includes three main components,
which becomes dominant beyond the 1000 Hz frequency level.
The first component is pipe resonance, which amplifies sounds
generated inside the grooves of tire treads and on channels along
the surface of tires (Sandberg & Ejsmont, 2002; Rasmussen et
al., 2007). The second component is the Helmholtz resonance,
which is present when the air in the tire tread cavity behaves
likes a spring that resonates with the mass of air between the
cavity and the atmospheric air while the tire rotates. The third
component is air pumping, which forms between the tire treads
and the pavement surface texture as the gaps fill with air. As tire
rolls over pavement, air is squeezed out or trapped and
compressed. When a tire loses contact with pavement at a certain
point, trapped air is forced out. This process, which is repeated
hundreds of times per second, produces a large amount of air
turbulence and noise (Rasmussen et al., 2007; Leasure &
Bender, 1975).
The radial vibration mechanism, which is more pronounced at
frequencies below 1000 Hz, is activated ad tire rolls over
pavement. Vibrations (noise) that are induced by small
deflections due to the interactions between the pavement texture
and the tread of a tire propagate to the air. This mechanism can
be described using the physical analogy of a hammer by
assuming that each tread is a hammer stroking the pavement
thousands of times per second. The adhesion mechanism
includes two components.
Similar to the air resonant mechanism, the adhesion
mechanism is more pronounced for frequencies of 1000 Hz and
higher. Stick-slip is the first component, which occurs due to the
vibrations caused by tangential slippage of the tire tread between
the tire and the road surface. The second component is stick-
snap, which occurs when the rubber adheres to the pavement and
is released vertically from the road surface as the tire rotates. The
physical analogy for stick-snap is a suction cup. Other
components of the interaction noise between tires and pavement
amplify these mechanisms.
2.3 Quiet Pavement
Research into quiet pavements first began in Europe in the
1970s; one decade later Japanese researchers began to
implement low noise pavement. A few decades ago, the
importance of the quiet pavements was realized by FHWA;
consequently, research projects initiated in this field in the
United States (Rasmussen et al., 2007; Meiarashi, 1999). Three
types of Hot Mix Asphalt (HMA) designs are utilized in
pavements on high volume highways: Open Graded Friction
Course (OGFC), dense graded hot mix asphalt, and Stone Matrix
Asphalt (SMA) mix (Hanson & James, 2004). Porous
pavements, which are also known as GFCs, gap graded asphalt or
drainage asphalt, are considered one of the quietest types of
pavement. Studies have shown that an OGFC can reduce noise
levels from 3 dB to 5 dB (A), compared with a dense HMA
pavement. This finding can be attributed to air voids in the
pavement, which provide a means of escape for air trapped
between the tire and the pavement surface, which causes increased
sound absorption. To successfully damp the noise, the pores need
to be interconnected. Furthermore, porous surfaces efficiently
drain water and reduce the splash and spray produced at the rear of
vehicles during rainfall. However, one of the critical challenges
associated with porous pavement is their durability and
effectiveness over time. Fine particle on roadways can rapidly clog
voids and reduce a pavement’s capability to absorb noise. Recent
studies have suggested the use of two-layer system to solve the
problem in which the surface becomes clogged with dirt and dust
from environment conditions and during snow removal operations
and to address durability issues related to the wearing of OGFC
surfaces (Hanson & James, 2004). Clogging can become a serious
problem that creates additional costs, especially in urban areas and
where periodic cleaning operations are required. A twin-lay
surface has been optimized to produce a long acoustical lifetime
for urban applications at approximate speeds 50 kilometers per
hour (km/h). For applications of porous pavements in which the
travel speeds range from 90 to 130 km/h, self cleaning of the
pavement surface is possible; the acoustic lifetime is acceptable
without cleaning (Sandberg, 1999; Kocak 2011).
3. Testing Material and Test Setup
3.1 Base Concrete Block
To construct a lean base concrete block, the specifications of
the Korea Expressway Corporation and Korea Standard were
employed. Type I Portland cement (ASTM-150), which was
supplied by Sungshin Industries, of Korea, was incorporated to
Table 1. Noise Levels Associated with Common Activities
Activities Noise Level
Quiet Room 40 dB
Whispered Speech 45 dB
Passenger Car, 80 km/h at 15 m 65 dB
Vacuum Cleaner 70 dB
Diesel Truck, 70 km/h at 15 m 75 dB
Milling Machine at 1.2 m 82 dB
Power Lawnmower at Operator’s Ear 95 dB
Noise Reduction Capacity of a Composite Pavement System
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solidify the materials. The optimum water to cement ratio was
determined, as shown in Table 2.
A standard base concrete block and three different types of
base concrete block, which are shown in Fig. 1, were
constructed. The basic dimension of the blocks constitutes
500 mm width, 500 mm length, and 150 mm thickness. To verify
the effect of lean concrete block on noise reduction, three
different types of holes were adopted. Detailed information is
shown in Table 3.
3.2 Asphalt Surface Course
In this study, an asphalt mix design for quiet pavements was
created. A modified asphalt binder with high viscosity was
employed for the hot mix asphalt. Detailed properties are listed
in Table 4.
The aggregate in asphalt pavement is a key component of hot
mix asphalt, especially with regards to permanent deformation.
Because the aggregate should exhibit durability, hardness, and
stability, a granite aggregate was adopted. The specific gravity,
absorption of water and LA abrasion ratio of the aggregate are
2.767, 1.867% and 27.24%, respectively.
Two different types of hot mix asphalts, including an upper
layer and lower layer, were used to verify the noise reduction.
Table 5 lists the gradations of each mixture. Fig. 2 shows a
comparison, and two different quiet asphalt pavements (top layer
and bottom layer).
3.3 Combined Pavement Section
Sixteen cases of combined pavement sections are shown in
Fig. 3, i.e., an asphalt surface layer (HMAs 1, 2, 3, and 4) on a
base concrete block (Bases A, B, C, and D), were adopted to
analyze the noise reduction effect on a passenger car, bus and
heavy truck. The distances from the noise sources to the test
specimens were 20 cm, 40 cm and 60 cm, respectively. The
combination of base concrete and 2-layer HMA (top and bottom
Table 2. Lean Concrete Mix Design
MaterialsCement
(kg)
Fine Aggregate
(kg)
Coarse Aggregate
(kg)
Water(kg)
Slump(cm)
Values 34 36 62 13 9.2
Table 3. Data on Holes in Concrete Blocks
TypeDistance hole to
hole (mm)Hole depth
(mm)Number of hole
Base B 55 30 8
Base C 70 40 6
Base D 60 30 to 40 7
Table 4. Properties of Modified Asphalt Binder
Test Unit Specification Requirement Results
Penetration (25oC)
1/10 mm ASTM D 5 Over 40 55.3
Ring and Ball oC ASTM D 36 Over 80 99.0
Ductility (15oC) cm ASTM D 113 Over 50 75
Viscosity (60oC) poiseASTM D
2171Over 200,000 500,000
Density (15oC) g/cm3 ASTM D 70 - 1.03
Flash Point oCASTM D
4552Min 219 Over 300
Table 5. Gradations of Upper Layer and Lower Layer for Surface
Course
Size (mm)Passing % of upper
layerPassing % of lower
layer
19 100 -
13 92-100 -
10 62-81 100
4.75 10-31 70-90
2.36 10-21 45-70
1.18 - 28-50
0.6 4-17 19-34
0.3 3-12 12-25
0.15 3-8 7-18
0.075 2-7 5-15
Fig. 1. Base Concrete Block with Different Types of Holes
Fig. 2. Types of Hot Mix Asphalt
Fig. 3. Sixteen Bases of the Combined Pavement System
Fig. 4. 2-Layer of HMA on Base Block
Seong-Kyum Kim, Woo-Jin Park, and Kwan-Ho Lee
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layers) is shown in Fig. 4.
3.4 Noise Level Test
The test set-up consists of a noisemaker (dB controllable
speaker), a signal analyzer to measure the noise levels, and a
wood block to separate the noise source and the analyzer. Fig. 5
shows the test set-up for the noise level test. The noise level tests
were conducted in three different stages, concrete blocks, surface
course of the hot mix asphalt, and composite section (hot mix
asphalt on concrete block). The noise levels for each noise
source include 90 dB for the passenger car, 100 dB for the bus,
and 110 dB for the heavy truck. The distances from the noise
source to the base concrete block consist of 50 cm for the
passenger car, 70 cm for the bus, and 90 cm for the heavy truck,
respectively. The distances from the base concrete block to the
sound analyzer, which are shown in Fig. 6, are 60 cm, 100 cm,
140 cm, 180 cm and 220 cm. The sensitivity of the noise level
analyzer was approximately ±0.2 dB, and the testing was
conducted at room temperature. To reduce the side effects of
ambient sounds, the tests were performed in a lab from 7 to 11
PM.
4. Test Results and Analysis
4.1 Noise Reduction Effect for Concrete Block with Magni-
tude of Noise Source
The effect of the installation of the hole in the lean concrete
base layer on noise reduction was analyzed, according to the
initial noise source for three different bases. The measured
values are shown in Table 6. These values signify the differences
between the standard base block and the modified base block
with different holes.
In the simulation of the passenger car, the noise reduction
improved as the measured distance increased. As shown in Table
6, Bade D with composite holes produced greater noise
reduction than the remaining bases, i.e., Base B and Base C. The
maximum noise reduction percentage is approximately 12.07%
for Base D with a 120 dB source and a 60 cm distance. The
simulation of bus noise demonstrated the least amount of
reduction and the simulation of a heavy truck demonstrated the
second lowest reduction. These results indicate that the use of
lean concrete base block with holes is an acceptable tool for
traffic noise reduction in residential areas where the majority of
the traffic volume is composed of passenger cars.
Table 7 represents the noise reduction effect at a distance of
100 cm between the noise source and the base concrete block.
The noise reduction values, which comprise the difference
between the standard concrete block (Base A) and the remaining
concrete blocks with holes, were calculated. Base D exhibited
optimal results at an equivalent distance from the noise source.
As the measurement distance increases, the noise reduction
effect generally increases. The surface void area of Base D
(350 cm2), which the noise contacts on, is larger than that of Base
C (300 cm2), even though the total void volume of concrete holes
of Base C (3162.7 cm3) is slightly larger than that of Base D
(2929 cm3)
4.2 Noise Reduction Effect with Measurement Distance
Noise levels, which generally decrease as the distance from the
noise source decreases, vary depending on the frequency band.
The lateral distance of sound source for each measuring point
was defined as 20 cm, 40 cm and 60 cm. When the dimension of
the specimen consist of three blocks, the lateral distance was
defined as 40 cm, 80 cm and 120 cm. Based on the initial noise
level and distance from the surface for each car, the maximum
distance for measuring noise level was 60 cm for a passenger car
and 180 cm for a heavy truck. The test results indicate that
although the noise reduction continuously increases, some of the
negative effects caused by diffraction are considered.
4.3 Noise Reduction Effect with Hole Shape and Size
To analyze the effects of shapes and sizes of holes on noise
reduction, three different holes with diameters of 17 mm, 32 mm
Table 6. Effect on the Different Types of Car
(a) Noise Reduction Percentage (%) for Simulation of a Passenger Car
Base B Base C Base D
yx
20 cm 40 cm 60 cm 20 cm 40 cm 60 cm 20 cm 40 cm 60 cm
60 cm 2.26 2.14 2.97 5.58 5.74 5.81 6.64 6.68 9.73
80 cm 4.42 4.03 4.90 6.96 6.85 5.99 7.90 8.99 10.34
100 cm 5.79 5.97 4.43 7.81 7.73 6.50 9.42 10.85 11.62
120 cm 5.83 5.34 6.24 7.72 7.81 6.93 10.57 11.10 12.07
(b) Noise Reduction Percentage (%) for Simulation of a Bus
Base B Base C Base D
yx
20 cm 40 cm 60 cm 20 cm 40 cm 60 cm 20 cm 40 cm 60 cm
80 cm 1.71 1.17 1.18 1.03 1.17 1.18 3.20 3.27 3.54
100 cm 1.74 2.58 2.51 1.74 2.58 2.51 3.47 3.98 4.79
120 cm 2.68 3.17 3.25 2.68 3.17 3.25 4.54 4.45 4.82
140 cm 3.17 3.25 3.86 4.34 4.33 5.07 5.40 5.65 5.91
(c) Noise Reduction Percentage (%) for Simulation of a Heavy Truck
Base B Base C Base D
yx
20 cm 40 cm 60 cm 20 cm 40 cm 60 cm 20 cm 40 cm 60 cm
100 cm 3.49 3.75 3.90 3.37 3.22 3.56 4.72 5.79 5.96
120 cm 4.53 4.68 4.65 3.96 3.99 4.07 4.76 5.13 6.74
140 cm 5.67 6.14 7.29 3.97 4.52 4.71 5.44 5.79 6.12
160 cm 6.02 6.47 7.09 4.88 5.18 5.32 6.58 7.06 6.97
Table 7. Noise Reduction Percentage (%)
Base B Base C Base D
ysource
20 cm 40 cm 60 cm 20 cm 40 cm 60 cm 20 cm 40 cm 60 cm
90 dB 5.79 5.97 4.43 7.81 7.73 6.50 9.42 10.85 11.62
100 dB 1.74 2.58 2.551 1.74 2.58 2.51 3.47 3.98 4.79
110 dB 3.49 3.75 3.90 3.30 3.18 3.56 4.72 5.79 5.96
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and mixed were utilized for the concrete blocks. From a
comparison of the normal concrete block and the blocks with
holes, the use of holes achieves significant noise reduction for
each vehicle to a maximum reduction percentage of 7.29%,
especially for the heavy truck. In case of the passenger car, the
range of noise reduction for Base D is 6.64% to 12.07%. For
buses and heavy trucks, Base D yielded a noise reduction of
3.20% to 5.91% and 4.72% 7.06%, respectively. The specimens
with the 32 mm holes and mixed holes resulted in more effective
noise reduction, with an average reduction in the range of 2.5%
to 4.79%, than the specimen with 17 mm holes. The test results
indicate that the larger the hole size, the greater is the noise
reduction effect. Because the hole size affects the durability and
strength of the concrete block, the proper hole size should be
determined.
4.4 Noise Reduction Effect for Asphalt Surface Layer
Noise reduction characteristics of an asphalt surface layer were
assessed. Four different asphalt specimens were employed for
comparison, namely, dense graded Hot Mix Asphalt (HMA 1),
the upper layer (HMA 2) of quiet pavement, the lower layer
(HMA 3) of quiet pavement, and the combined layers (HMA 4)
of quiet pavement. The average noise level of dense graded hot
mix asphalt is shown in Table 8. The measured average noise
levels range from 67.1 dB to 71.2 dB for a passenger car, from
76.2 dB to 80.5 dB for a bus, and from 84.2 dB to 87.1 dB for a
heavy truck. The remaining asphalt mixtures showed lower noise
levels than the sense graded hot mix asphalt. The noise reduction
effects for quiet pavement are shown in Table 9. The bottom
layer of the quiet pavement exhibited the widest range of noise
reduction percentage, specifically 3.99% to 6.50%. The effect of
the combined layers showed a similar noise reduction effect. As
shown in Table 7, the noise reduction effect decreases as the
noise source level increases. This finding indicates that the noise
reduction effect of quiet pavement is highly dependent on the
source noise level.
4.5 Noise Reduction Effect for Combined Pavement System
Figure 7 shows the measured noise levels for 4 different hot
mix asphalts on base A with 100 dB noise levels. The combination
of HMA 3 on Base A exhibited the lowest noise levels for each
measurement point on lines A, B and C. The combination of HMA
1 on Base A yields the highest noise levels. The combination
HMA 2 or 4 on Base A demonstrated a similar effect on noise
levels. The noise reductions range from 3 dB to 6 dB.
Figure 8 displays the noise levels for the different base
concrete blocks for each HMA. The source noise level was
90 dB. The use of different base concrete block with the same
Table 8. Noise Levels (dB) of Dense Graded Hot Mix Asphalt (HMA 1)
SourcePassenger Car
(90 dB)Bus
(100 dB)Heavy Truck
(110 dB)
yx
20 cm 40 cm 60 cm 20 cm 40 cm 60 cm 20 cm 40 cm 60 cm
100 cm 71.2 69.8 68.1 80.5 78.0 76.6 87.1 85.9 84.6
140 cm 70.3 68.8 67.1 78.8 76.8 76.8 85.0 84.4 84.2
180 cm 69.7 67.7 67.8 77.6 76.5 77.1 85.0 85.2 84.5
220 cm 70.1 68.9 68.2 78.7 77.0 76.2 85.6 85.2 85.0
Table 9. Effect on the Magnitude of Noise Source
(a) Noise Reduction Percentage (%) for 90 dB of Source
HMATop Layer (HMA 2)
Bottom Layer (HMA 3)
2-Layer (HMA 4)
yx
20 cm 40 cm 60 cm 20 cm 40 cm 60 cm 20 cm 40 cm 60 cm
100 cm 1.14 0.73 0.89 6.12 5.38 4.32 5.55 5.96 2.68
140 cm 0.14 1.18 2.06 5.60 6.50 5.16 3.16 5.47 2.80
180 cm 0.29 0.87 2.79 3.99 5.95 5.72 2.85 2.76 3.23
220 cm 0.29 0.87 2.79 3.99 5.95 5.72 2.85 2.76 3.23
(b) Noise Reduction Percentage (%) for 100 dB of Source
HMATop Layer (HMA 2)
Bottom Layer (HMA 3)
2-Layer (HMA 4)
yx
20 cm 40 cm 60 cm 20 cm 40 cm 60 cm 20 cm 40 cm 60 cm
100 cm 1.14 2.08 2.99 4.31 2.99 4.43 2.54 1.82 3.39
140 cm 0.39 0.92 2.46 3.74 3.01 4.54 1.80 2.48 4.67
180 cm 1.14 1.56 1.18 2.67 0.65 2.89 1.78 2.47 1.84
220 cm 1.14 1.56 1.18 2.67 0.65 2.89 1.78 2.47 1.84
(c) Noise Reduction Percentage (%) for 110 dB of Source
HMATop Layer (HMA 2)
Bottom Layer(HMA 3)
2-Layer (HMA 4)
yx
20 cm 40 cm 60 cm 20 cm 40 cm 60 cm 20 cm 40 cm 60 cm
100 cm 0.71 0.36 1.07 2.82 2.37 4.99 2.12 0.36 0.12
140 cm 1.76 0.12 0.12 1.88 3.05 4.85 1.53 0.23 0.36
180 cm 0.93 0.23 0.94 0.70 3.87 4.47 0.12 0.59 1.41
220 cm 0.93 0.23 0.94 0.70 3.87 4.47 0.12 0.59 1.41
Fig. 7 Noise Levels (dB) for 4 HMA on the Same Base Concrete Block (Base A): (a) At 20 cm, (b) At 40 cm, (c) At 60 cm
Seong-Kyum Kim, Woo-Jin Park, and Kwan-Ho Lee
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Fig. 8. Noise Levels (dB) for 4 HMA on Base A with 90 dB of Noise Source at Line A (20 cm): (a) Base A, (b) Base B, (c) Base C, (d) Base D
Fig. 9. Noise Level (dB) for 100 dB of Noise Source at A line (20 cm): (a) Base A, (b) Base B, (c) Base C
Fig. 10. Noise Level (dB) for 110 dB of Noise Source at Line C (60 cm): (a) Base A, (b) Base B, (c) Base C, (d) Base D
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HMA for a surface represented a slight noise reduction effect. In
the case of HMA 3, the measured noise levels were
approximately 67 dB for base A, 63 dB for base B, 64 dB for
base C, and 63 dB for base D. The use of holes in the concrete
base block produced noise reductions that range from 3 dB to
4 dB.
The combined effect is more interesting. The measured noise
levels for the combination of HMA 2, 3, or 4 on Bases B, C, or D
showed an approximate range of 62 dB to 68 dB. For the case of
HMA 1 on Base A, the noise levels ranged from 70 dB to 72 dB.
The range of noise reduction is approximately 4 dB to 8 dB,
which is significant.
Figure 9 shows a noise source level of 100 dB, which simulated
the traffic noise for a bus. The entire trend for the noise reduction
effect was similar to the noise reduction effect for a 90 dB noise
source.
Figure 10 represents the noise source level of 110 dB at line C,
which simulated the traffic noise for a heavy truck. The noise
reduction effects were separated into two parts:, different HMAs
on the same base concrete blocks and different base blocks with
the same HMA. The noise reduction effects were optimal for
HMA 3 on the same base concrete blocks. The measured values
ranged from 3 dB to 6 dB. With the same HMA, the measured
noise reduction values of different concrete bases ranged from
2 dB to 4 dB. These results indicate that the use of a quiet asphalt
surface resulted in a greater noise reduction effect than the use of
holes in the concrete base block. Based on the test results, the use
of HMA 3 on Base D resulted in optimal performance.
5. Conclusions
The research presented in this study aimed to characterize the
noise levels for 4 different types of hot mix asphalts on 4
different concrete base blocks. Three different traffic noises,
which simulated a passenger car (90 dB), a bus (100 dB), and a
heavy truck (110 dB), were applied. Despite potential limitations
of the laboratory tests, the following conclusions were formed:
1. To evaluate traffic noise reduction, four different concrete
base blocks with various sizes of holes were applied.
According to the applied traffic noise levels of 90 dB for a
passenger car and 110 dB for a heavy truck, the case of base
D with mixed holes resulted in the maximum valued of
8.7 dB and 6.8 dB of traffic noise reduction, respectively.
Due to the magnitude of the initial noise level, the effect of
traffic noise reduction was nearly meaningless. This finding
signifies that the use of a lean concrete base block with holes
is a sufficient tool for traffic noise reduction in residential
areas where the majority of the traffic volume consists of
passenger card.
2. The lateral distances of sound source for each measuring
point were defined as 20 cm, 40 cm and 60 cm from the test
specimen. When the dimension of the specimen increased
three times, the lateral distance increased to 40 cm, 80 cm
and 120 cm. Based on the initial noise level and distance
from the surface for the simulated traffic noise, the maxi-
mum distances for measuring noise level was 60 cm for pas-
senger cars and 180 cm for heavy trucks. Based on the test
results, the noise reduction continuously increases.
3. A comparison of the normal concrete block with the blocks
with holes reveals that the noise reduction for the block with
holes is significant, at a maximum reduction percentage of
7.29%, especially for the heavy truck. In the case of the pas-
senger car, the range of noise reduction for Base D is 6.64%
to 12.07%. For buses and heavy trucks, Base D yielded a
noise reduction of 3.20% to 5.91% and 4.72% to 7.06%,
respectively. The specimens with the 32 mm holes and
mixed holes resulted in more effective noise reduction, with
an average reduction in the range of 2.5% to 4.79%, than the
specimen with 17 mm holes.
4. The measured average noise levels range from 67.1 dB to
71.2 dB for a passenger car, from 76.2 dB to 80.5 dB for a
bus, and from 84.2 dB to 87.1 dB for a heavy truck. The
remaining asphalt mixtures yielded lower noise levels than
the dense graded hot mix asphalt. The bottom layer of the
quiet pavement demonstrated the greatest noise reduction
percentage, specifically in the range of 3.99% to 6.50%. The
effect of the combined layers showed a similar noise reduc-
tion effect.
5. The combination of HMA 3 on Base A showed the lowest
noise levels for each measurement point on lines A, B and
C. The combination of HMA 1 on Base A exhibited the
highest noise levels. The combinations of HMA 2 or 4 on
Base A showed a similar effect for noise levels. The noise
reductions range from 3 dB to 6 dB.
6. The noise reduction effects were separated into two parts: a
different HMA on the same base concrete block and a differ-
ent base block with the same HMA. The noise reduction
effects were optimal for HMA 3 on the same base concrete
block. The measured values were in the range of 3 dB to 6
dB. Using the same HMA, the measured noise reduction
values with different concrete bases ranged from 2 dB to 4
dB. This finding signifies that the use of quiet asphalt sur-
faces have a greater effect on noise reduction than the use of
holes in concrete base block. Based on the test results, the
use of HMA 3 on Base D exhibited the optimal perfor-
mance.
Acknowledgements
This work was partially supported by the KAIA (2012), which
is funded by the Korean Government.
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