Experiences with Porous Asphalt in the Netherlands 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 History of Porous Asphalt (PA) 2. Mix design and requirements Enrobe drainant oui ou non? 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

History of PA PA developed during 2nd world war for air fields Enrobe drainant oui ou non? 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 Enrobe drainant oui ou non? Increasing part of PA on motorways Percentage growth of PA on the Dutch motorways

Mix Design: Components Enrobe drainant oui ou non? 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 %) Enrobe drainant oui ou non? Mix design of PA 0/16 (mass %) On sieve desired max. min. 16.0 mm 0.0 7.0 11.2 mm 15.0 30.0 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 0/16 120 100 min. grading 80 max. grading Enrobe drainant oui ou non? 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

Mix design procedure Compact 4 Marshall specimens PA (2* 50 blows) Enrobe drainant oui ou non? 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 Enrobe drainant oui ou non? 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

Popular research test methods for PA Enrobe drainant oui ou non? Popular research test methods for PA Rotating Surface Abrasion Test (RSAT)

Other research test methods for PA Enrobe drainant oui ou non? Other research test methods for PA (Retained) Indirect Tensile Test (ITT) Wehner Schulze Retain conditions: 68 hours in water of 40 degree C.

Other research test methods for PA Enrobe drainant oui ou non? Other research test methods for PA Semi Circular Bendig Test (SCB) Wehner Schulze

Other research test methods for PA Enrobe drainant oui ou non? Other research test methods for PA Cantabro

Performance based contracts Enrobe drainant oui ou non? 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 Enrobe drainant oui ou non? 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 Enrobe drainant oui ou non? Early life dry skid resistance Accident in 1991 on new PA Longer braking distance Tests on different road surfaces

Monitoring skid resistance Enrobe drainant oui ou non? 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) Enrobe drainant oui ou non? Brake test (100% slip, dry surface)

86% slip trailer (wet skid resistance) Enrobe drainant oui ou non? 86% slip trailer (wet skid resistance)

86% slip trailer (wet surface) Enrobe drainant oui ou non? 86% slip trailer (wet surface)

Characteristic values for braking deceleration Enrobe drainant oui ou non? 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

Cause of the initial low dry skid resistance of PA 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!!!

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

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

Winter maintenance problems Enrobe drainant oui ou non? 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 Enrobe drainant oui ou non? 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: Enrobe drainant oui ou non? 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 Enrobe drainant oui ou non? 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 Enrobe drainant oui ou non? 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

Serious ravelling problems, end of service life Enrobe drainant oui ou non? 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

New developments (PA Plus) Enrobe drainant oui ou non? 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 Enrobe drainant oui ou non? 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)

Limiting conditions for Two-layer PA Enrobe drainant oui ou non? 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

Enrobe drainant oui ou non? Thank you! Current Future