Establishment of Relation between Pavement Surface Friction and Mixture Design PropertiesMozhdeh RajaeiNima Roohi Sefidmazgi

Ames, IAAugust 15-16,

2013

Hussain Bahia, Ph.D.

Outline1. Background and Introduction2. Materials and Methods3. Results and Conclusions

BACKGROUND AND INTRODUCTION

Friction in Pavement• The cost for highway accidents in 2000 exceeded

$230 billion. Many of these crashes are tied to wet road conditions, and inadequate friction characteristics (Noyce et al., 2007).

• Factors affecting friction: pavement surface characteristics,vehicle characteristics, tire characteristics, and environmental conditions

Surface Texture• Surface texture refers to the combination of different

aggregate shapes and sizes used in asphalt mixtures. Surface texture is defined in terms of wavelength (λ, distance along the surface) and amplitude (a, height above the surface).

(Henry 2000)

Factors Affecting Texture

(Sandberg 2000, Hall 2009, Ahamed 2009)

Property Texture RangeNominal Maximum Aggregate Size

(NMAS) Macro-Texture

Mixture Coarse Aggregate Type Macro-TextureMicro-Texture

Mixture Fine Aggregate Type Macro-TextureMicro-Texture

Asphalt Binder Content Macro-TextureAggregate Gradation Macro-Texture

Mixture Air Voids Macro-Texture

Objectives of Study

1. Relate lab/field friction measures to mixture properties

2. Relating lab texture measurements to field friction measures

Stationary Laser Profilometer (SLP)Circular Track Meter (CTM)Friction Number (FN)

Materials and Methods

Methods• Field Friction Measurement: –Friction Number (FN)

• Field Texture Measurement:–Circular Track Meter (CTM)

• Laboratory Texture Measurement:–Stationary Laser Profilometer (SLP)

Pavement Friction Measures• Friction number (FN): The average coefficient of friction measured by a locked-

wheel test device as specified in ASTM E274. This device was developed to use in situations with no anti-

lock brakes. Skid Trailer was K.J. Law Profiler.

FN (V) = 100 * μ = 100 * F/W• V is velocity of the test tire, km/hr (65 km/hr).• μ is the coefficient of friction.• F is the tractive horizontal force applied to the tire, kg.• W is the vertical load applied to the tire, kg.

Stationary Laser Profilometer (SLP)

• Used both in the laboratory and in the field. • Texture measurements described in ISO 13473-4.

Lab Texture Measure• Mean Profile Depth (MPD):

MPD values yield a two-dimensional representation of the surface texture (ISO 13473-1 2004).

MPD texture parameters provide averaged values for surface texture but do not quantify the distribution of asperities at the pavement surface.

0 500 1000 1500 2000 2500 3000 3500 4000

-4.0

-2.0

0.0

2.0

4.0

Data Point

Profi

le D

epth

(m

m)

Circular Track Meter (CTM)• Measures pavement

macro-texture in circular area– SLP make’s linear

measure.• Standardized under

ASTM E2157 2009.

Materials• Field sections and corresponding

cores from across WI.• Field Sections and corresponding

cores from MnROAD, MN.• Both dense graded and porous/gap

graded.• Different mixture properties:–Varying NMAS, Pb, gradation and

density.

Weibull Distribution • In order to describe gradation with the minimum

number of variables, a Weibull distribution is fitted to gradation curve. • x is the aggregate

size (mm)• κ is the shape factor • λ is the scale factor

0%

20%

40%

60%

80%

100%

Sieve Size 0.45

Perc

ent P

assi

ng

Increasing λ

0%

20%

40%

60%

80%

100%

Sieve Size 0.45

Perc

ent P

assi

ngIncreasing κ

ANALYSIS AND DISCUSSION

Regression Analysis• Regression analysis has been

performed using Minitab16.• The magnitude of the statistical

parameter, p-value, for each variable is an indicator of the significance of that variable –p-value closer to zero indicates high

significance.–Significance of values approaching 1.0 is

negligible.

Statistical Model Lab Friction vs. Mix Design Properties

• Laser MPD = 9.47 - 3.20 Gmb - 0.356 Pb + 0.0846 NMAS + 1.35 κ - 1.48 λ – Where MPD is the mean profile depth in millimeter, – Gmb is bulk asphalt mixture density (g/cm3), – Pb is the binder percent,– NMAS is the nominal maximum aggregate size in millimeter,– κ and λ are the Weibull distribution parameters.

Predictor Coefficient Standard Error Coefficient T value P valueConstant 9.467 4.040 2.340 0.036

Gmb -3.197 1.115 -2.870 0.013Pb -0.356 0.315 -1.130 0.278

NMAS 0.085 0.043 1.940 0.074κ 1.354 0.234 5.800 0.000λ -1.476 0.360 -4.100 0.001

Model Quality of Fit

0 0.5 1 1.5 2 2.5 30

0.5

1

1.5

2

2.5

R² = 0.597622636541067

R² = 0.918062031149123Dense Graded and PorousLinear (Dense Graded and Porous)

Measured SLP MPD (mm)

Est

imat

ed S

LP

MPD

(mm

)

Discussion of Model• NMAS: Positive coefficient

– Gradations with higher NMAS, (generally coarser gradations) result in higher MPD

• Bulk specific gravity (Gmb): Negative Coefficient– Lower Gmb, (thus higher air voids and porosity), leads to higher MPD.

• Binder Content (Pb): Negative Coefficient– Lower Pb reduces binder film thickness around aggregates as well as

reducing the aggregate packing level, thus increasing MPD.• Weibull Shape Factor (κ): Positive coefficient

– Higher κ values will result in gradations closer to a one-sized gradation and further from the maximum density line, thus resulting in higher MPD values.

• Weibull Scale Factor (λ): Negative coefficient– Decreasing λ will generally result in finer gradation. If all curves

above max density line, lower λ will being further from line.

Discussion of Model: Gradation

• It hypothesized that what is important for gradation is being further from the maximum density line, and not only the overall coarseness or fineness of the gradation.

0.00 0.50 1.00 1.50 2.00 2.50 3.000%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Sieve Opeining Size (mm0.45)

% P

assi

ng

Decreasing λ

Filed Friction vs. Lab Friction

• CTM MPD is the mean profile depth (mm) measured using the CTM in the field,• SLP MPD is the mean profile depth (mm) measured using the laser profilometer in the

laboratory.

Almost equivale

nt for dataset

Relating Laboratory Texture to Field Friction

• FN is the smooth-tire friction number from field measurements,

• CTM MPD is the mean profile depth (mm) measured using the CTM in the field.

• FN is the smooth-tire friction number from field measurements,

• SLP MPD is the mean profile depth (mm) measured using the laser profilometer in the laboratory

Using SLP-CTM Model

Conclusions• Using statistical analysis mixture design parameters

(i.e. volumetric and aggregate gradation properties) could be related to laboratory texture measurements (MPD).

• Knowing mixture design properties can lead to the estimation of road texture parameters.

• It was shown that increasing the distance of the gradation curve from the maximum density line (on both the coarse or fine side) is more important than the overall coarseness or fineness of the gradation in terms of increasing the expected texture.

Conclusions• Laboratory measured friction parameters (MPD)

can be related to field friction values (FN) using regression analysis.

• Utilizing the models developed in this study, by further investigation, mixture designers can have a guideline to estimate friction.

• Models developed in this study showed that the measurements for field and laboratory compacted samples from SLP device can be used to estimate friction parameters.

• A limited data set were used to develop models in this study, therefore more tests and analysis are needed to verify the results.

Acknowledgements• This research was sponsored by CFIRE

under project I.D. 07-09 and the Western Research Institute "Asphalt Research Consortium".

• Authors would also like to acknowledge the contributions of Mr. Timothy Miller, formerly of UW-Madison; as well as MnROAD for use of their test track database friction measurements.

Thank You!

www.uwmarc.orgQuestions?

Mozhdeh Rajaeirajaei@wisc.eduNima Roohi Sefidmazgiroohisefidma@wisc.eduHussain Bahiabahia@engr.wisc.edu