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Premium Asphalt Bases

- the role of the binder

AAPA Masterclass November 2012

1 Date 20/11/2012

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Pavement Engineering

Wearing course

Intermediate course / roadbase

Sub-base

Subgrade

ɛr

ɛv

Applied loading

Asphalt strain criterion

Subgrade strain criterion

Classical theory of stress generation and failure criteria in flexible pavements

The theory dates back to the AASHO Road Test and the Alconbury Hill experiment

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Pavement Engineering

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ɛv

Load spreading effect of different pavement layers is related to the stiffness of the pavement materials

w/c

roadbase

sub-base

subgrade

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Beam theory

A simplified model assumes the road structure acts as a beam and will be subjected to the same engineering principles

An applied force F to the beam will cause a deflection ‘d’ to result. The resulting deflection will be influenced by the magnitude of the applied force, the length of the beam (L) and the modulus of the beam ‘E’.

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Beam Modulus E

d

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Modulus and Stiffness

The stress / strain relationship of engineering materials is a fundamental property.

For elastic materials Hookes Law is valid where:

E= σ/ɛ where the elastic modulus E is the quotient of the strain ɛ divided by the tensile stress σ

For visco-elastic materials such as bitumen where the strain is dependent on the time of loading and the temperature, the modulus is called ‘stiffness’ and loading times and temperature must be referenced:

St,T = σ/ɛT

Bitumen stiffness strongly influences asphalt stiffness, hence using harder grades of binder will create stiffer asphalt with improved load spreading qualities.

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History - Evolution of Base course mixes in France

GB EME 2 EME 1 1970 80/100 1976 Very hot summer 1978 60/70 or 35/50 10/20 1990 35/50 20/30 2000 35/50 or 20/30 10/20 or 20/30 or 25/35

EN 13924:2006 Specification for hard paving grade bitumens

Essential Requirement Surrogate Characteristic Test Methods Unit

Classes

0 1 2 3 4

Consistency at Intermediate Service Temparature

Penetration at 25°C EN 1426

0.1mm NPD TBR 15 to 25 10 to 20

Consistency at Elevated Service Temperature

Softening Point EN 1427

°C NPD TBR 55 to 71 58 to 78 60 to 76

Dynamic Viscosity at 60°C

WN 12596 Pa.s NR TBR ≥550 ≥ 700

Durabilty (Resistance to hardening at 163 EN 12607-1)

Change of Mass EN 12607-1 or 3 % NPD TBR ≤ 0.5

Retained Penetration EN 1426 % NPD TBR ≥ 55

Softening Point after hardening

EN1427 °C NPD TBR

≥ Orig. Min+2

Increase in Softening Point

EN 1427 °C NPD TBR ≤ 8 ≤ 10

Increase in Softening Point & Penetration Index before test (on original bitumen

EN 1427

°C NR TBR

≤ 10 from -1.5 to + 0.7

≤ 10 ≥ -1.5

Other Properties

Kinematic Viscosity at 135°C

EN 12595 NR TBR ≥ 700 ≥ 700

Fraass Breaking Point EN 12593 °C NR TBR ≤ 0 ≤ 3

Flash Point EN ISO 2592 °C ≥ 245 ≥ 236

Solubility EN 12592 % mass fraction NR TBR ≥ 99

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EN 13924:2006 Annex B (Informative)

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Property Unit Test Method Data

TS=300Mpa, by BBR °C EN 14771 TBR

Tm=0.3, by BBR °C EN 14771 TBR

G* at 15°C and 10 Hz, by DSR Mpa EN 14770 TBR

TG*/sind = 1 kPa at 1.6Hz, by DSR °C EN 14770 TBR

Table B.1 – Informative properties

EN 12591 Paving Grade Bitumens

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EN 12591 Paving Grade Bitumens

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Base course mixes - Main properties

Type

of m

ix

Gir

ator

y. (V

oids

%)

C80

(D 1

0mm

) C

100

(D 1

4mm

) C

120

(D 2

0 m

m)

Wat

er se

nsiti

vity

r/

R r

atio

Rut

dep

th

(60°

C-1

00 m

m)

* 10

.000

cyc

les (

%)

** 3

0.00

0 cy

cles

(%)

Stiff

ness

mod

ulus

(1

5°C

-10H

z) in

MPa

Fatig

ue –

adm

issi

ble

stra

in (@

1 m

illio

n de

cy

cles

)

G.B Class 2 ≤ 11 ≥ 0.65 ≤ 10* ≥ 9,000 ≥ 80.10-6

GB Class 3 ≤ 10 ≥ 0.7 ≤ 10* ≥ 9,000 ≥ 90.10-6

GB Class 4 ≤ 9 ≥ 0.7 ≤ 10** ≥ 11,000 ≥ 100.10-6

EME Class 1 ≤ 10 ≥ 0.7 ≤ 7.5** ≥ 14,000 ≥ 100.10-6

EME class 2 ≤ 6 ≥ 0.75 ≤ 7.5** ≥ 14,000 ≥ 130.10-6

According to NF EN 13108-1 EB 14 Assise 35/50 (GB) and EB 14 Assise 10/20 (EME)

Type Max Aggr

size Binder

Binder Content

(%)

Void content %

Thickness (cm)

GB 14 et 20 35/50 20/30

4 to 5 6 to 8 8 to 16

EME 10-14-20 10/20 4.5 to 6.2

3 to 6 6 to 15

Base course Asphalt Mixes According to NF EN 13108-1 EB 14 Assise 35/50 (GB) and EB 14 Assise 10/20 (EME)

Do we need thicker pavements to reach a longer life? Or is there a minimum strength above which structural damage by traffic doesn’t occur

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UK Long Life Pavement Design TRL 250

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Do we have Hard Paving Grade Bitumens in Australia?

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Pinkenba Bitumen Plant

Availability of Hard Grades in Australia

Following a de-bottlenecking program and productivity improvements at the Pinkenba plant in Brisbane 15/25 bitumen is now being manufactured.

It is expected to become available in NSW at the end of 2013

At present EME binders are not being considered for inclusion in AS2008 so they will be speciality bitumens based on EN 13924

Shell has made a 20 pen bitumen that complies with the EN 13924 15/25 grade.

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