Noise reduction capacity of a composite pavement system

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

− 2 − KSCE Journal of Civil Engineering

(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


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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



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


yx


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


yx


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 (%)


ysource


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


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


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


Bottom Layer (HMA 3)

2-Layer (HMA 4)

yx


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


Bottom Layer(HMA 3)

2-Layer (HMA 4)

yx


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



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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Noise reduction capacity of a composite pavement system

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