1. Two-layer porous asphalt
for urban roads
- The Øster Søgade project
Lars Ellebjerg Larsen
Hans Bendtsen
Danish Road Institute/Road Directorate
2. Project goals
• 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
3. Acknowledgements
Øster 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
4. The test road
Øster Søgade in Copenhagen:
• Speed: 50 km/h
• Traffic: 7000 AADT
• HGV: 8 %
• Length: 800 m
6. The porous pavements
Name Section Type Total Top layer Bottom
thickness aggregate layer
aggregate
Porous
PA8-70 I 25+45 mm 5-8 mm 11-16 mm
asphalt
Porous
PA5-55 II 20+35 mm 2-5 mm 11-16 mm
asphalt
Porous
PA5-90 III 25+65 mm 2-5 mm 16-22 mm
asphalt
Dense
DAC8
IV asphalt 30 mm 0-8 mm -
(ref.)
concrete
16. Permeability - northbound lane
70
Water draining time (seconds/10 cm)
60
50 PA8-70 a
PA8-70 b
40
PA8-70 c
30 PA5-55 a
PA5-55 b
20 PA5-55 c
PA5-90 a
10
PA5-90 b
0 PA5-90 c
0 10 20 30 40 50 60 70
Months after opening
17. Permeability - southbound lane
70
Water draining time (seconds/10 cm)
60
50
40
PA8-70 a
30 PA8-70 b
PA8-70 c
20
PA5-55 a
10 PA5-55 b
PA5-55 c
0 PA5-90 a
0 10 20 30 40 50 60 70
PA5-90 b
Months after opening PA5-90 c
20. CT-Scan – Results
100%
Bottom layer (PA16) Top layer (PA8) Voids
90% Mortar
Aggregate
80%
70%
60%
50%
40%
30%
20%
10%
0%
0 10 20 30 40 50 60 70
mm
33 mm 51 mm
21. Preparation of plane sections
100 mm Drill Core
Thin section 1 45 mm wide by 30 mm high 10 mm
100 mm
40 mm
Plane section (100 by 100 mm) 10 mm
Thin section 2 45 mm wide by 30 mm high 10 mm
26. Reference pavement – 8 or 11 mm
L_pA, max, fast, 7.5 m as a function of speed
passenger cars, comparison of reference surfaces
80
L_pA,max,fast,7.5m, [dB re 20 µPa]
75
70
AC8d, Kgl
AC11d(E), Kgl
AC8d, SFr
65
AC11d, SFr
AC11d, all, SFr
AC11d, Ubh
60
40 50 60 70
Speed, [km/h]
27. 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
28. Noise annoyance with closed
windows
100%
90% Cannot hear noise from
road traffic
80% Not annoyed
70% A little annoyed
60% Annoyed
50% Very annoyed
40%
30%
20%
10%
0%
Before After Before After
Reference pavement P orous pavement
29. Noise annoyance with open
windows
100%
90% Cannot hear noise from
road traffic
80% Not annoying
70% A little annoying
60% Annoying
50% Very annoying
40%
30%
20%
10%
0%
Before After Before After
Reference pavement P orous pavement
30. Dose-response – closed windows
100%
Before repaving
90%
After repaving
80%
Dos e-res pons e curve
A little or more annoye
70%
60%
50%
40%
30%
20%
10%
0%
45 50 55 60 65 70 75
Nois e outs ide windows - L Aeq (dB(A))
31. Cost-benefit analysis
Comparing 3 means: 3 cases:
• Two-layer porous • Central city street
asphalt • Ring road
• Noise barriers • Freeway
• Sound insulation
Net Present Value: Comparing:
• construction and • Direct costs
maintenance
• Costs/dB/dwelling
• costs for a 30-year
period
32. 3 cases
City street (50 km/h, AADT: 12.000)
Apartments: 1st – 5th floor 15 m facade per apartment
65 – 68 dB façade level 665 apartments (133/floor)
Ring road (70 km/h, AADT: 30.000)
Apartments: ground – 2nd floor 15 m facade per apartment
73 – 74 dB façade level 399 apartments (133/floor)
Freeway (110 km/h, AADT: 60.000)
Detached houses in 5 rows 23 m road per house
77 dB at the first row
69/71 dB at the second row 435 houses (87/row)
66/69 dB at the third row
58/66 dB at the fourth row
57/65 dB at the fifth row
33. Porous pavements
Effect: Costs (net present value, €):
City street: 4 dB City street: 296,000
Ring road: 5 dB Ring road: 360,000
Freeway: 6 dB Freeway: 477,000
34. Noise barriers
Effect: Costs (net present value, €):
City street: Not possible City street: Not possible
Ring road: 0-12 dB Ring road: 1,335,000
Average: 3.9 dB
Freeway: 1-12 dB Freeway: 1,590,000
Average: 6.2 dB
35. Façade insulation
Effect: Costs (net present value, €):
9 dB on indoor levels with City street: 2,685,000
windows closed
Ring road: 1,607,000
Freeway: 2,890,000
36. Costs
3500
P orous asphalt
3000
Noise barrier
Costs (thousand Euro
Facade insulation
2500
2000
1500
1000
500
0
City street Ring road Freeway
37. Costs per dB per dwelling
900
P orous asphalt
800
Noise barrier
700
Costs/dB/dwelling (Eur
Facade insulation
600
500
400
300
200
100
0
City street Ring road Freeway
38. 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 mm
aggregate 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
39. 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