Enrobe drainant oui ou non? Experiences with Porous Asphalt in the Netherlands Jan Voskuilen Project...

Enrobe drainant oui ou non?

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


TOPICS

1.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


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 2005 65% of our motorways have PA as wearing course


Increasing part of PA on motorways

Percentage growth of PA on the Dutch motorways


Mix Design: Components

Standard PA 0/16 consists of:

• crushed stones 6 to 16 mm • crushed sand between 2 and 0.063 mm

• filler < 0.063 mm containing 25% Ca(OH)2

• pen grade bitumen 70/100

• no RA allowed

• no drainage inhibitors are used


Mix design of PA 0/16 (mass %)

On sieve desired max. min. 16.0 mm 0.0 7.0 11.2 mm 15.030.0 8.0 mm 50.0 65.0 5.6 mm 70.0 85.0 2.0 mm 85.0 0.063 mm 95.5

Bitumen 70/100 4.5 (= on 100% aggregate)


Grading of PA 0/16

0

20

40

60

80

100

120

C16 C11,2 C8 C5,6 2 mm 63 um

sieve

per

cen

tag

e o

n s

ieve

min. grading

max. grading


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


Popular research test methods for PA

Rotating Surface Abrasion Test

Test temperature is 20 degree C.

The resistance to ravelling is expressed as the total amount of loose material after 24 hours of testing


Popular research test methods for PA Rotatin

gSurfaceAbrasion Test(RSAT)


Other research test methods for PA

(Retained) Indirect Tensile Test (ITT)

Wehner Schulze

Retain conditions:

68 hours in water of 40 degree C.



Semi Circular Bendig Test (SCB)

Wehner Schulze



Cantabro


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


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


Early life dry skid resistance

• Accident in 1991 on new PA• Longer braking distance• Tests on different road surfaces


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)


Brake test (100% slip, dry surface)


86% slip trailer (wet skid resistance)


86% slip trailer (wet surface)


Characteristic values for braking deceleration

Porous Asphalt Dense Asphalt

New Old New Old

Without ABS

5.4 m/s2 7.0 m/s2

7.0 m/s2

8.0 m/s2

With ABS 9.0 – 9.5 m/s2 9.5 – 10.0 m/s2

Braking deceleration must be > 6.5 m/s2

Enrobe drainant oui ou non?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!!!


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)

months

BD

in

m/s2

5

6

7

0 126


Policy from 1991

• Warn road users with special sign “longer braking distance – new road surface”

• Carry out research to improve initial dry skid resistance


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


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


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


Performance of standard PA 0/16

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


Maintenance techniques for PA

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


Ten

sile

str

en

gth

Service life

Start of ravelling

Serious ravelling problems,

end of service

life

1

2

3

1Time for preventive maintenance (seal technique)2 Time for temperory maintenance (Via-

Ral)3Time to mill old PA and lay new PA

Maintenance techniques for PA


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


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

NEW DEVELOPMENTS

Noise reduction is 5 to 6 dB(A)


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

NEW DEVELOPMENTS


Thank you!

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