1. Experiences with Porous Asphalt in the Netherlands
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Experiences with Porous Asphalt
in the Netherlands
Jan Voskuilen
Project Manager Asphalt
Road and Hydraulic Engineering Institute
Ministry of Transport, Public Works and Water Management

2. TOPICS History of Porous Asphalt (PA) 2. Mix design and requirements
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TOPICS
History of Porous Asphalt (PA)
2. Mix design and requirements
3. Advantages and disadvantages of PA
4. Problems and solutions
5. Maintenance
6. New developments

3. History of PA PA developed during 2nd world war for air fields
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History of PA
PA developed during 2nd world war for air fields
Rediscovered in the Netherlands in the seventies
Since 1987 limited application of PA for safety
In 1990 the policy changed: application of PA on all motorways because of noise reduction
In % of our motorways have PA as wearing course

4. Increasing part of PA on motorways
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Increasing part of PA on motorways
Percentage growth of PA on the Dutch motorways

5. Mix Design: Components
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Mix Design: Components
Standard PA 0/16 consists of:
crushed stones 6 to 16 mm
crushed sand between 2 and mm
filler < mm containing 25% Ca(OH)2
pen grade bitumen 70/100
no RA allowed
no drainage inhibitors are used

6. Mix design of PA 0/16 (mass %)
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Mix design of PA 0/16 (mass %)
On sieve desired max. min.
16.0 mm
11.2 mm
8.0 mm
5.6 mm
2.0 mm
0.063 mm
Bitumen 70/ (= on 100% aggregate)

7. Grading of PA 0/16 120 100 min. grading 80 max. grading
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Grading of PA 0/16
120
100
min. grading 80
max. grading
percentage on sieve 60 40 20
C16
C11,2 C8
C5,6
2 mm
63 um
sieve

8. Mix design procedure Compact 4 Marshall specimens PA (2* 50 blows)
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Mix design procedure
Compact 4 Marshall specimens PA (2* 50 blows)
Determine the void content of the specimens
The minimum void content must be at least 20%
Determine the mean composition

9. Popular research test methods for PA
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Popular research test methods for PA
Test temperature is 20 degree C.
The resistance to ravelling is expressed as the total amount of loose material after 24 hours of testing
Rotating Surface Abrasion Test

10. Popular research test methods for PA
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Popular research test methods for PA
Rotating
Surface
Abrasion
Test
(RSAT)

11. Other research test methods for PA
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Other research test methods for PA
(Retained) Indirect Tensile Test (ITT)
Wehner Schulze
Retain conditions:
68 hours in water of 40 degree C.

12. Other research test methods for PA
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Other research test methods for PA
Semi Circular Bendig Test (SCB)
Wehner Schulze

13. Other research test methods for PA
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Other research test methods for PA
Cantabro

14. Performance based contracts
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Performance based contracts
Guarantee period is 7 years
Functional requirements before opening, during the guarantee period and at the end of the guarantee period for:
- ravelling
- cracks
- void content
- drainability
- layer thickness
- longitudinal evenness
- rutting

15. Disadvantages of PA After laying lower initial skid resistance
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Disadvantages of PA
After laying lower initial skid resistance
Sometimes winter maintenance problems
Ravelling can cause broken wind screens
Higher costs
Clogging
Sensitive for damage

16. Early life dry skid resistance
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Early life dry skid resistance
Accident in 1991 on new PA
Longer braking distance
Tests on different road surfaces

17. Monitoring skid resistance
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Monitoring skid resistance
Gap-graded mixes:
Initial dry friction, deceleration test (100% slip)
initial wet friction (86% slip)
wet friction during service life once in two years (86% slip)

18. Brake test (100% slip, dry surface)
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Brake test (100% slip, dry surface)

19. 86% slip trailer (wet skid resistance)
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86% slip trailer (wet skid resistance)

20. 86% slip trailer (wet surface)
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86% slip trailer (wet surface)

21. Characteristic values for braking deceleration
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Characteristic values for braking deceleration
Braking deceleration must be > 6.5 m/s2
Porous Asphalt
Dense Asphalt
New
Old
Without ABS
5.4 m/s2
7.0 m/s2
8.0 m/s2
With ABS
9.0 – 9.5 m/s2
9.5 – 10.0 m/s2

22. Cause of the initial low dry skid resistance of PA
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Cause of the initial low dry skid resistance of PA
In contrast with Dense Asphalt no crushed sand or fine aggregate is sprinkled on PA surface to improve initial skid resistance
After laying the PA aggregate is covered with a bitumen film
During 100% slip alarm stop (without ABS) the bitumen film weakens due to increasing temperature (bitu-planing)
Melted bitumen forms a sliding surface
Important:
Problem only occurs with vehicles without ABS-system
Motorists don’t expect this of new asphalt!!!

23. Enrobe drainant oui ou non?
Policy from 1991
If the braking deceleration (BD) is < 5.2 m/s2 there is a speed limitation of 70 km/h.
If BD is between 5.2 and 6.5 m/ s2 the sign “longer braking distance – new road surface” has to be placed
(time 3 to 6 months depending on traffic and climate) 7 BD in
m/s2 6 5 6 12
months

24. Enrobe drainant oui ou non?
Policy from 1991
Warn road users with special sign “longer braking distance – new road surface”
Carry out research to improve initial dry skid resistance

25. Winter maintenance problems
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Winter maintenance problems
The problem is that de-icers drain in the pores of PA
Solutions:
- good information for car drivers (radio, television)
- sprinkling higher amount de-icer
- closure of lanes
Lab research: Safe cote and CMC

26. Road safety investigation
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Road safety investigation
On PA road sections happen as much accidents as on Dense Asphalt road sections!!!
Cause: motorists drive faster on PA during rainfall, so the extra safety of PA is consumed!
As a consequence of this, the capacity of PA road sections during rainfall is higher

27. Advantages of PA Noise reduction No rutting problems During rainfall:
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Advantages of PA
Noise reduction
No rutting problems
During rainfall:
- no aqua planing
- reducing of splash and spray
higher capacity
road markings stay visable
Comfortable
Better quality of run off water
High appreciation of car drivers!
Dense Asphalt Concrete
Porous Asphalt

28. Performance of standard PA 0/16
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Service life of PA:
average service life of fast lane is 16 years
average service life of slow lane is 12 years
3 dB(A) noise reduction in comparison with DA

29. Maintenance techniques for PA
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The following maintenance techniques are available:
“Seal technique” – before ravelling starts an emulsion with a rejuvenator is spread on the PA surface
If the ravelling process has already started an open emulsion sand asphalt mixture is applied in the upper part of PA (see paper about Via-Ral, Kneepkens et all, E&E, Vienna 2004)
In/out – at the end of service life: milling of old PA and laying new PA

30. Serious ravelling problems, end of service life
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Maintenance techniques for PA
Start of ravelling
Serious ravelling problems, end of service life
Tensile strength 1 2 3
Service life 1
Time for preventive maintenance (seal technique) 2
Time for temperory maintenance (Via-Ral) 3
Time to mill old PA and lay new PA

31. New developments (PA Plus)
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New developments (PA Plus)
Results of evaluation of test sites:
PA with 5.5% bitumen has a longer service life in comparison with standard PA with 4.5% pen grade bitumen.
Service life of PA with PMB and PA with pen grade bitumen with drainage inhibitors is equal.(see paper Voskuilen et all, E&E, Vienna 2004)
Recommendation: Use PA with 5.5% pen grade bitumen with drainage inhibitors

32. Two-layer PA constructions
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NEW DEVELOPMENTS
Two-layer PA constructions
Standard construction
25 mm top layer PA 4/8
45 mm bottom layer PA 11/16
Alternative construction
20 mm top layer PA 2/6
50 mm bottom layer PA 11/16
Noise reduction is 5 to 6 dB(A)

33. Limiting conditions for Two-layer PA
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NEW DEVELOPMENTS
Limiting conditions for Two-layer PA
Only top layer 4/8
No noise barriers needed
Locations with normal clogging
Realization road-width without traffic
Laying period 1 May – 1 October
Good weather conditions

34. Enrobe drainant oui ou non?
Thank you!
Current
Future