Cold recycling of bituminous mixtures

International Workshop

Asphalt Recycling and Materials Re-Use in Asphalt Pavements

prof. Ezio Santagata Politecnico di Torino

Cold recycling of

bituminous mixtures

Università di L’Aquila - Facoltà di Ingegneria - 28 ^th June 2007

Cold recycling of bituminous mixtures

Self introduction

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Torino

• Give general overview of the topic

• Highlight interest/problems of society, users, road owners, designers and contractors

• Give some examples about specific solutions or problems

• Point out main key players in research

Cold recycling of bituminous mixtures

Guidelines for presentation

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SPECIFIC AND OPEN QUESTIONS

RESEARCH NEEDS

• General description

• Critical issues derived from research experience

– Materials – Testing – Modelling

• Closure = Questions

Cold recycling of bituminous mixtures

Presentation structure

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Cold recycling of bituminous mixtures

General description

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• RAP (reclaimed asphalt pavement)

– bulk structure

• Bituminous emulsion

– binder

• Filler (usually Portland cement)

– filler and stiffening enhancement

• Added water

– Workability and emulsion dispersion

• Virgin aggregates

– integration to bulk structure

Cold recycling of bituminous mixtures

General description

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In-field recycling

(single or multiple unit)

In-plant recycling

• Advantages:

– Reduced use of raw materials – Reduction of disposal volumes – Lower environmental impact – Lower energy consumption

– Reduced impact on labour health and safety – Cost reduction

• Disadvantages:

– Reduced structural performance

– Problems in mix design, testing and modelling

Cold recycling of bituminous mixtures

General description

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However, based on engineering experience,

there are guidelines and specifications!

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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• Rehabilitation of motorway A4 Torino-Milano (1999-2001)

Conglomerato bituminoso

Misto granulare

Sottofondo

Riciclato a freddo Conglomerato bituminoso

Subgrade

Unbound foundation

Bitumen-bound layers 20 cm bituminous mixtures

20 cm cold-recycled mixture

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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• Rehabilitation of motorway A4 Torino-Milano (1999-2001)

– Production homogeneity

0 1 2 3 4 5 6 7

1 2 3 4 5 6 7

Day of monitoring

W at er c on te nt ( % )

Measured Expected

0 1 2 3 4 5 6 7 8

1 2 3 4 5 6 7

Day of monitoring

T ot al b in de r co nt en t (% )

Measured

Expected

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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• Rehabilitation of motorway A4 Torino-Milano (1999-2001)

– Production homogeneity

0 1 2 3 4 5 6 7

1 2 3 4 5 6 7

Day of monitoring

W at er c on te nt ( % )

Measured Expected

0 1 2 3 4 5 6 7 8

1 2 3 4 5 6 7

Day of monitoring

T ot al b in de r co nt en t (% )

Measured

Expected

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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• Rehabilitation of motorway A4 Torino-Milano (1999-2001)

– Compaction

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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High stiffness Low stiffness

• Load spreading function

EVALUATION OF

STIFFNESS AND STRENGTH

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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• Problems to solve:

– Testing technique

– Sample preparation / coring

Selection of practical characterization techniques

Development of equipment and procedures

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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• Field compaction

(static)

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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• Field compaction

(static)

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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• Laboratory compaction

(gyratory)

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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0 500 1000 1500 2000 2500 3000 3500 4000 4500

0 20 40 60 80 100 120

Maturazione (giorni)

M od ul o el as tic o [M Pa ]

Preparazione standard Preparazione 150kN - 5' Collegamento 80/100: 3500 MPa

Collegamento 60/70: 4160 MPa

Curing time, t (days)

E la st ic m od ul us , E ( M P a)

Binder course mix 80/100: 3500 MPa Binder course mix 60/70: 4160 MPa

Standard preparation 150 kN – 5 min

• Elastic stiffness testing (RLIT)

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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• Indirect tensile strength (ITS) testing (static)

0 1 2 3 4 5 6 7 8

0 1 2 3 4

Displacement (mm)

Lo a d ( k N )

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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y = 1371.5x^-0.2153 R² = 0.8657

10 100 1000

1000 10000 100000 1000000

Num ero di cicli a rottura N_f

Deformazione iniziale [strain]

Precondizionamento standard Precondizionamento a 60°C Precondizionamento a 40°C Usura ANAS (v = 3,0%) Usura aperta (v = 5,4%) Collegamento ANAS (v = 7,4%)

N

(number of loadings to failure)

In iti al s tr ai n (m icr os tr ai n)

• Fatigue testing

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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0 500 1000 1500 2000 2500 3000 3500 4000

1 10 100 1000

Curing time (days)

El a st ic s tif fn e ss a t 20 °C ( M Pa )

E = E

+ k ⋅ log

(days)

Short term

Long term

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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• Elastic stiffness parameters (E ₁ and k) extremely sensitive to variations of:

– Size distribution – Emulsion type – Compaction

1999 2000 2001

E

1429 569 1256

k

1388 921 1591

E

3897 2206 4084

Lower binder content, coarser RAP, higher air voids

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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0,00 0,20 0,40 0,60 0,80 1,00 1,20

1 10 100

Curing time, t (days) IT S ( N /m m

)

101.6 mm specimens 150 mm specimens ITS = 0.467 + 0.281 log t

ITS = 0.238 + 0.290 log t

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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• ITS parameters (RTI ₁ and k _RTI ) extremely sensitive to variations of:

– Size distribution – Emulsion type – Compaction

Lower binder content, coarser RAP, higher air voids

0,0 0,2 0,4 0,6 0,8 1,0 1,2

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Day of monitoring ITS (N/mm2 )

101.6 mm specimens Value at 60 days (2001) = 0.967 N/mm²

0,0 0,2 0,4 0,6 0,8 1,0 1,2

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Day of monitoring ITS (N/mm2 )

150 mm specimens Value at 60 days (2001) = 0.752 N/mm²

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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1400 2400 3400 4400

0 10 20 30 40 50 60 70

Curing time, t (days)

E la st ic s ti ff ne ss , E [ M P a]

0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8

W at er c on te nt ( % )

0,4 0,5 0,6 0,7 0,8 0,9 1,0

0 10 20 30 40 50 60 70

Curing time, t (days) IT S [ N /m m 2 ]

4,0 4,5 5,0 5,5 6,0 6,5 7,0 7,5 8,0

W at er lo ss ( % )

• Evolution of water content

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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1400 2400 3400 4400

0 10 20 30 40 50 60 70

Curing time, t (days)

E la st ic s ti ff ne ss , E [ M P a]

0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8

W at er c on te nt ( % )

0,4 0,5 0,6 0,7 0,8 0,9 1,0

0 10 20 30 40 50 60 70

Curing time, t (days) IT S [ N /m m 2 ]

4,0 4,5 5,0 5,5 6,0 6,5 7,0 7,5 8,0

W at er lo ss ( % )

• Evolution of water content

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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0 1000 2000 3000 4000 5000 6000

0 20 40 60 80 100 120

Ma tura zi one (giorni)

Modulo elastico [MPa]

Maturazione a 20°C

Maturazione preliminare a 60°C Dopo la maturazione preliminare

Collegamento 80/100: 3500 MPa Collegamento 60/70: 4160 MPa

• Effect of curing temperature

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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• Effect of emulsion type and quantity

0 500 1000 1500 2000

0 min 30 min 60 min In situ

Modalità di compattazione

In t ( E )

ESSO 2.5%

COLAS 2.5%

0 500 1000 1500 2000

0 min 30 min 60 min In situ

Modalità di compattazione

In t ( E )

ESSO 4.5%

COLAS 4.5%

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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• Effect of filler type (cement vs quicklime)

E

= 53,615 x (days) + 530,51 0

500 1000 1500 2000 2500 3000

0 10 20 30 40 50 60 70

Curing time (days)

Ela st ic s tif fn e ss a t 20° C ( M Pa )

Filler: 2%

Emulsion: 4%

Water: 1%

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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• Compaction properties (from gyratory equipment)

70 75 80 85 90 95 100

1 10 100 1000

N g (log)

% M V es s

Dati sperimentali

Modellazione (eq. 1)

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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• Compaction properties (from gyratory equipment)

C1

= -2,16 K

+ 98,1 R

= 0,82

C1

= -2,37 K

+ 100,8 R

= 0,93

77 78 79 80 81 82 83 84

7,0 7,5 8,0 8,5 9,0 9,5 10,0

K g

C 1 g ( % )

Politecnico

Autostrade

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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• Mix design

2,120 2,130 2,140 2,150 2,160 2,170 2,180 2,190

3,75 4,00 4,25 4,50 4,75 5,00 5,25

Water content, %w (%)

D ry d en si ty , G

( g/ cm

)

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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• Mix design

7,00 7,20 7,40 7,60 7,80 8,00 8,20 8,40 8,60 8,80

3,75 4,00 4,25 4,50 4,75 5,00 5,25

Water content, %w (%)

W or k ab ili ty , k

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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• Mix design

%FF _optimum = %w _added + (a+Kb) ⋅ %E

0,150 0,175 0,200 0,225 0,250 0,275 0,300 0,325 0,350

2,150 2,175 2,200 2,225 2,250 2,275 2,300

Dry density, G

(g/cm

) In di re ct t en si le s tr en gt h, I T S (N /m m

)

K = 0

K = 0.25

K = 0.5

K = 0.75

K = 1

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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• Short term characterization

– UNBOUND?

• Resilient modulus M _R

• Failure (p-q) criteria

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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• Short term characterization

– UNBOUND?

0 100 200 300 400 500 600 700

0,00 100,00 200,00 300,00 400,00 500,00 600,00 700,00 800,00

Θ [kPa]

Mr [Mpa]

Mr (Modello)

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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• Short term characterization

– UNBOUND?

0,0 100,0 200,0 300,0 400,0 500,0 600,0 700,0

0 100 200 300 400 500 600

p [kPa]

t [k P a]

Cold recycling of bituminous mixtures

Critical issues derived from research experience

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• Characterization of the emulsion-filler system

Interconnected binding matrix High modulus, high strength

Porous binding matrix

Low modulus, low strength

• Can production plants be improved?

• Can compaction techniques be improved?

• Should RAP be separated in fractions to control gradation?

• Are rejuvenators needed?

• Are modified emulsions needed?

• What can of filler should be used?

• How much stiffness is needed?

• Options to mix design?

• Options to performance testing?

• Coring?

• Field testing?

Cold recycling of bituminous mixtures

Closure - Questions

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Thanks for your attention

[email protected]