Transcript Experiences with PA 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
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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
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History of PA PA developed during 2 nd 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
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Increasing part of PA on motorways
Percentage growth of PA on the Dutch motorways
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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
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Mix design of PA 0/16 (mass %) On sieve 16.0 mm 11.2 mm 8.0 mm 5.6 mm 2.0 mm 0.063 mm desired 85.0
95.5
max . 0.0
15.0
50.0
70.0
min.
7.0
30.0
65.0
85.0
Bitumen 70/100 4.5 (= on 100% aggregate)
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Grading of PA 0/16
120 100 80 60 40 20 0 C16 C11,2 C8 C5,6
sieve
2 mm 63 um min. grading max. grading
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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
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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
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Popular research test methods for PA
Rotating Surface Abrasion Test (RSAT)
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Other research test methods for PA
Retain conditions: 68 hours in water of 40 degree C.
(Retained) Indirect Tensile Test (ITT)
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Other research test methods for PA
Semi Circular Bendig Test (SCB)
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Other research test methods for PA
Cantabro
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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
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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
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Early life dry skid resistance
• • •
Accident in 1991 on new PA Longer braking distance Tests on different road surfaces
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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)
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Brake test (100% slip, dry surface)
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86% slip trailer (wet skid resistance)
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86% slip trailer (wet surface)
Characteristic values for braking deceleration
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Braking deceleration must be > 6.5 m/s 2
Without ABS With ABS Porous Asphalt New 5.4 m/s 2 Old 7.0 m/s 2 Dense Asphalt New 7.0 m/s 2 Old 8.0 m/s 2 9.0 – 9.5 m/s 2 9.5 – 10.0 m/s 2
•
Cause of the initial low dry
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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!!!
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Policy from 1991 If the braking deceleration (BD) is < 5.2 m/s 2 there is a speed limitation of 70 km/h.
If BD is between 5.2 and 6.5 m/ s 2 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 6 m/s 2 5 0 6 months 12
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Policy from 1991
•
Warn road users with special sign “longer braking distance – new road surface”
•
Carry out research to improve initial dry skid resistance
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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
Road safety investigation
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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
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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
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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
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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
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Maintenance techniques for PA 1 2 3 Start of ravelling Serious ravelling problems, end of service life 1 2 3
Service life
Time for preventive maintenance (seal technique) Time for temperory maintenance (Via-Ral) Time to mill old PA and lay new PA
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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
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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)
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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
Thank you!
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Current Future