Two-layer porous asphalt for urban roads

- The Øster Søgade projectLars Ellebjerg Larsen

Hans BendtsenDanish Road Institute/Road Directorate

• To develop and test noise reducing pavements for urban roads

• Applying and improving Dutch two-layer concept for Danish conditions

• Investigate the clogging phenomenon of two-layer porous pavements

• Over the lifetime of the pavements to analyse:– The acoustical properties of the pavements– The clogging of the pavements– The structural properties of the pavements

Project goals

AcknowledgementsØster Søgade experiment financed by:• Danish Ministry of Transport • Danish Ministry of the Environment

Danish project group: • Lene Michelsen, Danish Road Directorate • Steen Kønigsfeldt and Michael Rasmussen, Municipality of

Copenhagen• Jørn Bank Andersen, Pavement Contractors Association / NCC• Hans Bendtsen, Bent Andersen, Jørgen Kragh, Jørn Raaberg,

Bjarne Schmidt and Lars Ellebjerg Larsen, Danish Road Institute/Road Directorate

The clogging project: • Part of the Dutch IPG program• Financial and technical support and cooperation of Road and

Hydraulic Engineering Institute in the Netherlands (DWW) • The DRI-DWW noise abatement programme

The test roadØster Søgade in Copenhagen:• Speed: 50 km/h• Traffic: 7000 AADT• HGV: 8 %• Length: 800 m

The test road 2

The porous pavements Name Section Type Total

thickness Top layer aggregate

Bottom layer

aggregate

PA8-70 I Porous asphalt 25+45 mm 5-8 mm 11-16 mm

PA5-55 II Porous asphalt 20+35 mm 2-5 mm 11-16 mm

PA5-90 III Porous asphalt 25+65 mm 2-5 mm 16-22 mm

DAC8 (ref.) IV

Dense asphalt

concrete30 mm 0-8 mm -

The porous pavements 2

0

10

20

30

40

50

60

70

80

90

100

0,001 0,01 0,1 1 10 100

Size (mm)

Per

cent

age

of m

ater

ial

AC8tDA5DA8DA16DA22

The test pavements

The test pavements 2

Material PA5(top)

PA8(top)

PA16(bottom)

PA22(bottom)

DAC8(ref.)

Stone material 95.0 % 95.5 % 97.0 % 97.5 % 97.5 %

Hydrated lime 1.5 % 1.5 % 1.5 % 1.5 % 1.5 %

Lime filler 3.5 % 3.0 % 1.5 % 1.0 % 1.0 %

Cellulose fibers .25 % .25 % .25 % .25 %

Bitumen 6.3 % 5.4 % 3.9 % 3.5 % 5.8 %

Marshall cavity 25.5 % 26.0 % 25.5 % 25.5 % 2.4 %

Pavement measurements

• On location– Texture – Laser measurements of MPD– Permeability – Becker’s tube method– Friction

• On drill cores– Built-in voids– Asphalt analyses– Thin and plane sections– CT-scans

Noise measurements

• SPB• CPB• CPX• Sound absorption

– Extended surface method [ISO 13472-1]– Impedance tube – Transfer-function

method [ISO 10534-2]

Other surveys

• Noise annoyance– questionnaire survey

• Cost-benefit analyses– Comparison of pavements, barriers and

façade insulation

Texture

Texture 2

0,000

0,500

1,000

1,500

2,000

2,500

3,000

0,000 0,100 0,200 0,300 0,400 0,500 0,600 0,700

Positioning (km)

MP

D (m

m)

19992001200220042005Old pavement

PA8 PA5 DAC8

[ISO 13473-1]

Permeability

Permeability - northbound lane

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70

Months after opening

Wat

er d

rain

ing

time

(sec

onds

/10

cm)

PA8-70 aPA8-70 bPA8-70 cPA5-55 aPA5-55 bPA5-55 cPA5-90 aPA5-90 bPA5-90 c

Permeability - southbound lane

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70

Months after opening

Wat

er d

rain

ing

time

(sec

onds

/10

cm)

PA8-70 aPA8-70 bPA8-70 cPA5-55 aPA5-55 bPA5-55 cPA5-90 aPA5-90 bPA5-90 c

CT-scan of porous asphalt

7 years old PA from A12

CT-scan 2

33 mm

51 mm

CT-Scan – Results

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 10 20 30 40 50 60 70

mm

VoidsMortarAggregate

Top layer (PA8)Bottom layer (PA16)

33 mm 51 mm

100

mm

40 m

m

10 mm

10 mm

10 mm

Thin section 1

Thin section 2

Plane section (100 by 100 mm)

100 mm Drill Core

45 mm wide by 30 mm high

45 mm wide by 30 mm high

Preparation of plane sections

Acquiring the images

Plane section: 100 x 100 mm

Analyses of thin sections in microscope

New 4 years old

SPB noise measurements

60

65

70

75

I II III IV

SP

BI'

[dB

]

1999 2000 2001 2002 2003 2004 2005

Noise reduction

4.5 4.9

6.0

4.63.6 3.8

2.7 2.7 2.72.4 2.2

1.0

2.8

1.3 1.11.7

0.91.41.4 1.2

-0.2

-2

0

2

4

6

8

10

I II III

Noi

se re

duct

ion

[dB

]

1999 2000 2001 2002 2003 2004 2005

2.9 2.32.4

Reference pavement – 8 or 11 mmL_pA, max, fast, 7.5 m as a function of speed

passenger cars, comparison of reference surfaces

60

65

70

75

80

40 50 60 70Speed, [km/h]

L_pA

,max

,fast

,7.5

m, [

dB re

20

µPa]

AC8d, KglAC11d(E), KglAC8d, SFrAC11d, SFrAC11d, all, SFrAC11d, Ubh

Questionnaire survey

• Questionnaire survey – before and after repaving– 240 questionnaires per survey– 72 and 65 percent returned

• Noise levels calculated with the Nordic Prediction Method for Road Traffic Noise– Levels before:

• +1 dB for a worn and uneven pavement– Levels after:

• -2.5 dB relative to before by the ref. pavement• -7.6 dB relative to before by the porous pavement

Noise annoyance with closed windows

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Before After Before After

Reference pavement Porous pavement

Cannot hear noise fromroad traffic

Not annoyed

A little annoyed

Annoyed

Very annoyed

Noise annoyance with openwindows

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Before After Before After

Reference pavement Porous pavement

Cannot hear noise fromroad traffic

Not annoying

A little annoying

Annoying

Very annoying

Dose-response – closed windows

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

45 50 55 60 65 70 75

Noise outs ide windows - LAeq (dB(A))

A li

ttle

or

mo

re a

nn

oye

Before repaving

After repaving

Dose-response curve

Cost-benefit analysis

Comparing 3 means:• Two-layer porous

asphalt• Noise barriers• Sound insulation

Net Present Value:• construction and

maintenance• costs for a 30-year

period

3 cases:• Central city street• Ring road• Freeway

Comparing:• Direct costs• Costs/dB/dwelling

3 cases

City street (50 km/h, AADT: 12.000)Apartments: 1st – 5th floor65 – 68 dB façade level

Ring road (70 km/h, AADT: 30.000)Apartments: ground – 2nd floor73 – 74 dB façade level

Freeway (110 km/h, AADT: 60.000)Detached houses in 5 rows77 dB at the first row69/71 dB at the second row66/69 dB at the third row58/66 dB at the fourth row57/65 dB at the fifth row

15 m facade per apartment665 apartments (133/floor)

15 m facade per apartment399 apartments (133/floor)

23 m road per house435 houses (87/row)

Porous pavements

Effect:

City street: 4 dB

Ring road: 5 dB

Freeway: 6 dB

Costs (net present value, €):

City street: 296,000

Ring road: 360,000

Freeway: 477,000

Noise barriers

Effect:

City street: Not possible

Ring road: 0-12 dBAverage: 3.9 dB

Freeway: 1-12 dBAverage: 6.2 dB

Costs (net present value, €):

City street: Not possible

Ring road: 1,335,000

Freeway: 1,590,000

Façade insulation

Effect:

9 dB on indoor levels with windows closed

Costs (net present value, €):

City street: 2,685,000

Ring road: 1,607,000

Freeway: 2,890,000

Costs

0

500

1000

1500

2000

2500

3000

3500

City street Ring road Freeway

Cost

s (t

housa

nd E

uro

Porous asphaltNoise barrierFacade insulation

Costs per dB per dwelling

0

100

200

300

400

500

600

700

800

900

City street Ring road Freeway

Cost

s/dB/

dw

ellin

g (

Eur

Porous asphaltNoise barrierFacade insulation

Conclusion and perspective• When new, the thickest porous pavement

with 5 mm aggregate had the best noise reduction of 5-6 dB

• When old the porous pavement with 8 mmaggregate in the top-layer maintain a noise reduction of 1-2 dB

• In relation to 11 or 16 mm dense asphalt reduction is 1 to 2 dB higher

• The pavement with 8 mm aggregate clogs significantly less than the pavements with smaller aggregate

• The PA5 pavements are “dead” in 2005

Conclusions and perspective• The perceived effect of noise reductions by

porous asphalt matches the reduction in decibel level

• Compared to noise barriers and façade insulation porous asphalt gives a much higher noise reduction per invested Euro

• Analyses of thin and plane sections as well as the use of CT-scanning of drill cores will be used to evaluate the clogging process

• The working group are looking at possibilities for continuing the project with a renewal of the top layers with PA8