Portorož, Slovenia

Laboratory test method for the predictionof the evolution of road skid-resistance with traffic

•Minh-Tan DoMinh-Tan Do

•LCPCLCPC

•Research engineerResearch engineer

•E-mail : minh-tan.do@lcpc.frE-mail : minh-tan.do@lcpc.fr

Portorož, Slovenia

Scope

• Need to predict skid-resistance evolution

• Existing empirical tools

• LCPC polishing tests

• From laboratory simulation to road prediction

• Conclusions

Portorož, Slovenia

Need to predict skid-resistance evolution

• Road skid-resistance evolves with time

due to mechanical actions (traffic)

due to climate effects

• Prediction of skid-resistance evolution is needed:

to forecast road maintenance

to ensure long-term performance

to optimize material choice

Portorož, Slovenia

Existing empirical tools

• Experimental sites tracked over time

drawbacks: costs , time

• Aggregate testing (i.e. PSV)

drawback: transposition aggregates mixes?

Portorož, Slovenia

LCPC polishing tests – Objectives

• Quick laboratory tests

• Able to test concrete-asphalt mixes and aggregates

• Comparable results with road data

• Means to predict skid-resistance evolution

Portorož, Slovenia

LCPC polishing tests – Test machine

• Wehner/Schulze machine

Origin: University of Berlin (70’s)

Functions: polishing & friction measurement

Specimens: cores Ø 22.5 cm

Tested materials: concrete asphalt, aggregates, sand

Portorož, Slovenia

LCPC polishing tests – Wehner/Schulze machine

• “Polishing” function

Principle: rolling rubber cones with (water + abrasive) mix

Cone contact pressure: 0.4 N.mm-2

Rotation speed: 500 rpm

• “Friction measurement” function

Principle: sliding rubber pads with water

full « braking » curve (µ-time) from 100 km/h to complete stopping

Portorož, Slovenia

LCPC polishing tests – Specimens

• Concrete asphalt

Cores taken from pavements or laboratory-made slabs

• Aggregates

Mosaic discs (fraction 7.2/10 mm)

22,5 cm

22,5 cm

Portorož, Slovenia

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0 50 000 100 000 150 000 200 000

number of passesfr

ictio

n c

oe

ffic

ien

t µ W

S

LCPC polishing tests – Test procedure

• Friction-time plot

Friction measurement every 1000 passes µmax is reached

Next stops: 3-5-9.104 passes

End: 180,000 passesµmax

15 profiles, spaced every 0.5 mmL = 76 mm, x = 0.01 mm

• Microtexture measurements (polished part)

Initial state (0 pass)

At µmax

90,000 and 180,000 passes

Portorož, Slovenia

LCPC polishing tests – Laboratory results (1/2)

• Aggregates vs asphalt mixes

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0 20 000 40 000 60 000 80 000 100 000

number of passes

fric

tion

co

effi

cie

nt µ

WS

asphalt core aggregate disc

Portorož, Slovenia

LCPC polishing tests – Laboratory results (2/2)

• Wehner/Schulze vs PSV

0

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0 50 000 100 000 150 000 200 000

number of passes

fric

tion

co

effi

cie

nt

µWS = 1.06(PSV/100) – 0.20

0

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PSV/100

µW

S a

fter

90

,00

0 p

ass

es

Portorož, Slovenia

From laboratory to road

• Core sampling on new roads tracked over time

Wheel paths

Polishing tests(just after road construction)

Ageing effect(every 6 months)

Skid-resistance evolution(every 6 months)

simulation vs actual evolution

Traffic count

Portorož, Slovenia

From laboratory to road

• Core sampling on circulated roads

Wheel paths

Polishing tests

Friction measurements(Wehner/Schulze machine)

polishing duration traffic

Traffic count

Portorož, Slovenia

From laboratory to road

• Relationship polishing duration – traffic

N = k.T

N: number of passesT: cumulated truck number

k = constant = 0.024

Calibrated from 13 sites

(source from Tang PhD thesis, 2007)

Portorož, Slovenia

From laboratory to road

• Simulation vs actual evolution

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0,0E+00 5,0E+05 1,0E+06 1,5E+06 2,0E+06 2,5E+06

traffic (cumulated number of trucks)

fric

tion

co

eff

icie

nt

Road data Wehner/Schulze simulation

Portorož, Slovenia

From laboratory to road

• Towards a prediction of skid-resistance evolution

Problem statement

?

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0,E+00 5,E+04 1,E+05 2,E+05 2,E+05

number of passes N

fric

tion

co

effi

cie

nt µ

WS

Simulation from Wehner/Schulze machine

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0,E+00 5,E+05 1,E+06 2,E+06

traffic T

LF

C 6

0 k

m/h

Measurement by means of ADHERA device (blank PIARC tyre, locked wheel)

Portorož, Slovenia

From laboratory to road

• Towards a prediction of skid-resistance evolution

Approach

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0,E+00 5,E+04 1,E+05 2,E+05 2,E+05

number of passes N

fric

tion

co

effi

cie

nt µ

WS

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0,E+00 5,E+05 1,E+06 2,E+06

traffic T

LF

C 6

0 k

m/h

N = 0.024 T?

Portorož, Slovenia

From laboratory to road

• Towards a prediction of skid-resistance evolution

Relationship µWS – LFC/SFC (source from Huschek, 2004)

LFC (80 km/h) = 1.04 µWS – 0.01

LFC from Stuttgart Friction Tester, ribbed tyres

SFC (80 km/h) = 0.96 µWS + 0.06

SFC from SCRIM

Portorož, Slovenia

From laboratory to road

• Towards a prediction of skid-resistance evolution

Comparison prediction/measurement

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0,6

0,E+00 5,E+05 1,E+06 2,E+06 2,E+06 3,E+06

traffic T

LF

C 8

0 k

m/h

Overestimation

µWS-N plot converted into equivalent LFC-T plot

actual LFC-T plot

Portorož, Slovenia

Conclusions – Where are we / objectives?

• Quick laboratory tests

½ day to plot a full friction-time curve, could be depending (N = 0.024T) on anticipated traffic

• Able to test concrete-asphalt mixes and aggregates

Yes, except very aggressive surfaces

• Comparable results with road data

Yes, first tendencies to be supported by other experiments

• Means to predict skid-resistance evolution

Promising first results

Portorož, Slovenia

Conclusions – Next step

• Investigate the relationship polishing duration traffic

“k” (N = kT) should be constant ?

• Relationship µWS LFC/SFC

• Relative influences light vehicles/trucks

• Prediction model, taking into account other mechanisms (seasonal variations, ageing)