D O T T O R AT O D I R I C E R C A I N I N G E G N E R I A C I V I L E , C I C L O X X V I I

I N D I R I Z Z O I N F R A S T R U T T U R E V I A R I E E T R A S P O R T I

PERFORMANCES AND DURABILITY OF ASPHALT MIXTURES MADE WITH RECLAIMED ASPHALT PAVEMENT

Ph.D. Candidate: Luca Noferini Tutor: prof. Andrea Simone

Reclaimed Asphalt Pavement (RAP)

• Asphalt mix obtained from dismatling / milling of existing asphalt layers

• Made of aggregate and bitumen • 100% reusable and recyclable (European Asphalt Pavement

Association, 2010) to produce new asphalt mixes

Research topic and objectives

USE OF RAP IN NEW ASPHALT MIXES PRODUCED WITH HOT-IN-PLANT TECHNOLOGY

• How much RAP can be incorporated in a new asphalt mix with no negative effects on mix’s performance?

• To what extent RAP affects the final mix’s properties?

PHASE 1: European and Italian context of RAP usage

PHASE 2: Study of RAP influence on a specific asphalt mix

• RAP availability and applications

• Economic and environmental advantages of RAP usage

• Production technologies

RAP applications

Hot, warm, cold asphalt mixes

Bitumen and aggregate

High

Average

Low/cost

Aggregate

None

Granular material (filling)

Landfilling

Value What is reused Application

Pros and Cons of RAP usage

2. Reduced costs of virgin bitumen (5% mass weight / >50% price)

1. Reduce the need of natural and not-renewable resources (aggregate and bitumen)

3. Lower GHG emissions, atmosferic pollution (ground level ozone creation and acidification) related to raw materials supplying

1. Costs for retrofitting of asphalt plants

2. Special handling procedures and management required

3. Strategy (market regulation)

5. RAP mixes are high quality and long lasting products (if...)

4. Public admin. are concerned about RAP mixes performance

39

32 31

22 21 18

15

9

2014 European asphalt production, million tonnes

• European road netword is 5.7 million km long

• 230 million cars and 31 million heavy vehciles

• 40 mil tonnes of asphalt required for road maintenance in Italy

2014 RAP availability in Europe, million tonnes

10.9

9.2 9.0

4.5 3.4

2.3 1.3 1.2 1.0 1.0

0.4

Use or RAP in valuable applications (% of 2014 availability)

100% 100% 95% 90% 85% 85%

75% 64% 63%

54% 50%

6%

• High-value: hot / warm / cold in place / in plant recycing

• Low-value: use as unbound granular material

• No value / cost: landfilling

Percent of available RAP used for different purposes in Europe

Hot Mix Asphalt, 61%

Warm Mix Asphalt, 4%

Cold Recycling, 5%

Unbound Layers, 13%

Other civil eng. applications, 10%

Landifll/other, 7%

Percent of available RAP used for different purposes in Europe (%)

0

10

20

30

40

50

60

70

80

90

100

Hot Mix Asphalt Warm Mix Asphalt

Cold Recycling Unbound Layers

Other civil eng. applications Landifll/other

Experimental programme

4 versions of AC Binder 0/20 @ 0%, 10%, 20% and 30% RAP

Same PSD, 5% air voids and 5% bitumen content

LAB TESTS ON ASPHALT MIXES LAB TESTS ON BITUMEN

Characterization of raw mat.

Mix desing of RAP mixes

Volumetrics

Production of asphalt beams

Fatigue testing (4PB)

Extraction and recovery

Penetration and R&B

Dynamic viscosity

Dynamic Shear Rheometer

ONLY CEN STANDARDISED TESTS!

RAP asphalt mixtures durability

0

20

40

60

80

100

0.01 0.1 1 10 100

Perc

ent

pas

sin

g (%

)

Sieve size, Log (mm)

Mix0 (control mixture) Mix1 (control+10% RAP)

Mix2 (control+20% RAP) Mix3 (control+30% RAP)

Mix Design – Particle Size Distribution of RAP mixes

Total blending RAP/neat bitumen assumed Proportioning with extracted RAP PSD

Mix Design – Total bitumen content of RAP mixes

5.0% 4.5%

4.1% 3.6%

0%

1%

2%

3%

4%

5%

6%

0

10

20

30

40

50

60

Bit

um

en c

on

ten

t (%

by

aggr

egat

e m

ass)

Bit

um

en c

on

ten

t (g

ram

s o

n 1

kg

sam

ple

)

RAP 0/8 RAP 8/12 Virgin 50/70 Virgin bitumen content (%)

Total blending RAP/neat bitumen assumed Proportioning with extracted RAP PSD

75

78

80

83

85

88

90

93

95

98

100

1 10 100 1000

Perc

ent

of

max

imu

m d

ensi

ty ρ

M (

%)

Number of gyrations, Log

Mix Design – Volumetric study with gyratory compactor

Target 5% air voids

0% RAP

30% RAP

• Compactability increase with RAP content • Higher presence of fines with increasing RAP content

Production of samples – Bulk Density of asphalt beams

Mix0 2337

Mix1 2379

Mix2 2359

Mix3 2387

1900

2000

2100

2200

2300

2400

2500

Bu

lk d

ensi

ty (

kg/m

3)

• Density used as parameter to check if materials are comparable • Testing the material vs testing the sample

Wöhler Fatigue lines

1.E+04

1.E+05

1.E+06

1.E+07

10 100 1000

Nu

mb

er o

f cy

cles

to

fai

lure

(N

f20

)

Strain amplitude (με)

Mix0

Mix1

Mix2

Mix3

Mix0 Fatigue Line

Mix1 Fatigue Line

Mix2 Fatigue Line

Mix3 Fatigue Line

0% RAP

30% RAP

• 4PB, strain-controlled, 25 Hz, 10°C at 100, 150, 200 µε, NF 20% • RAP contributes stiffening the neat binder (slope changes with bitumen type) • Mix with 30% RAP shows the longest fatigue life (highest Nf)

Number of cycles to failure

Mix0 - 0% RAP Mix1 - 10% RAP Mix2 - 20% RAP Mix3 - 30% RAP 0.E+00

2.E+06

4.E+06

6.E+06

8.E+06

1.E+07

1.E+07

Load

cyc

les

to f

ailu

re (

Nf2

0)

at

stra

in le

vel o

f 1

00

με

Va= 5.9% BD = 2463 kg/m3

Bc = 5.07%

Va = 4.0% BD = 2477 kg/m3

Bc = 4.97%

Va = 4.9% BD= 2480 kg/m3

Bc = 5.0%

Va= 3.8% BD= 2480 kg/m3

Bc = 5.03%

• Adding up to 20% RAP seems to have no negative effect on mixes’ durability • Higher sensitivity to RAP content than to other material properties (voids) • Mix 3 has the highest results variability

Analysis of fatigue data with RDEC approach

• Same conclusion of Wohler fatigue lines • The RDEC approach is more time-consuming and may be inconsistent

Interaction neat-RAP bitumen

• Laboratory testing on bitumen obtained from prismatic samples with cold extraction method (DCM) and recovered with Rotavapor

Penetration and softening point of recovered bitumen

• RAP bitumen causes hardening of the bitumen blend in proportion to RAP content

Pen at 25°C

Ring & BallMix 0

Mix 1Mix 2

Mix 3RAP

27 25

21 16

7

55 56 57 63 73

Dynamic viscosity at 135, 150, 160 and 170 °C

• Viscosity increases in proportion to RAP % (... above 0.23 Pa*s at 160°C) • No significant changes in viscosity up to 20% RAP content • Increase in RAP-neat bitumen blend viscosity at 30% RAP

0

1

10

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

Dyn

amic

vis

cosi

ty (

Pa∙s

)

% RAP

135

150

160

170

RAP BITUMEN NEAT BITUMEN

Bitumen rheology – Complex modulus isochrones

• Hardening and increased elastic response in proportion to RAP content • No effects on blend’s rheology up to 10% RAP, limited effects at 20% RAP • Apparently no brittleness issues at 30% RAP

1.E+02

1.E+05

1.E+08

0 10 20 30 40 50 60 70 80 90

Co

mp

lex

mo

du

lus

|G*|

(Pa

)

Temperature (°C)

B0

B1

B2

B3

BRAPHardening

Bitumen rheology – Phase angle isochrones

• Hardening and increased elastic response in proportion to RAP content • No effects on blend’s rheology up to 10% RAP • Significant effects on bitumen rheology when RAP content is 20% or above

0

2

4

6

8

10

0 10 20 30 40 50 60

Tgδ

Temperature (°C)

B0

B1

B2

B3

BRAP

Increased elastic response

Research findings

1. The specific type of asphalt mixture can be produced with hot-in-plant technology incorporating up to 20% RAP with no detrimental effects on its performance and durability

2. RAP can be incorporated in the investigated mix at percentages up to 10% with no significant effects on bitumen properties. In this case, RAP can be added without the need to perform any additional lab test on the recovered binder

3. For 20% or more of RAP content being incorporated in the new mix, it’s highly recommended to perform lab investigations on the recovered bitumen to determine: penetration at 25°C, softening point and dynamic viscosity at 160°C

Recommendations

1. Standard mix design procedures shall be adjusted for RAP mixes in order to take into account of RAP variability and the presence of aged bitumen

2. The amount of bitumen being added in new mixes shall be calculated considering the contribute of the old bitumen which is present in the RAP aggregate

3. RAP sampling shall be aimed to obtained representative portions of RAP and to avoid segregation to impact samples’ representativeness (see EN 932-1 and 12697-27 for sampling procedures)

4. RAP characterization contributes to limiting its variability making RAP usage reliable and therefore more attractive to public authorities