isaet 2012 - emulsified asphalt mixes by bernard eckmann

EMULSIFIED ASPHALT MIXESOVERVIEW OF THE EMULSIFIED ASPHALT MIXES IN FRANCE

B. Eckmann, Technical Department, EUROVIA (France)

2012 International Symposium on Asphalt Emulsion Technology

Oct. 10 - 12, 2012 - Arlington Virginia

0. CONTENTS

1. Background and Introduction

2. Objectives

3. Gravel-Emulsion (GE)

4. Emulsion Asphalt Concrete (EAC)

5. Conclusion – Future perspectives

6. Acknowledgements / Further information



1. BACKGROUND AND INTRODUCTION

Emulsion technology is well developed in France (~ 1 Mio tons of emulsions per year) Almost exclusively cationic emulsions More than 65% in spraying applications (bond coats, surface dressings) Micro-surfacing is a well mastered and mature technique Grave-Emulsion (GE) and Emulsion Asphalt Concrete (EAC) cold mixes are the two main emulsion-based alternatives to hot asphalt mixes

o Grave-Emulsion : - Re-profiling or base course material- Well established products

o Emulsified Asphalt Concrete : - Wearing course applications- Most technically challenging



2. OBJECTIVES

Description of the Grave-Emulsion (GE) and Emulsion Asphalt Concrete (EAC) productso Formulationo Propertieso Field of applicationo Perspectives

More details on mix design methods, in-situ behaviour and on-going research is given in complementing papers



3. GRAVE-EMULSION (GE) – General description

Continuously-graded mix of aggregates and slow-setting emulsion Residual bitumen content is kept between 3.8% and 4.5 % Emulsion breaks preferably on the sand and fine fractions which leads to a mix :

o With a binder-rich mortar phaseo Aggregates are allowed to be not completely coated



Binder-rich mortar

Partially coated aggregate

3. GRAVE-EMULSION (GE) – Properties resulting from its specific structure

Plastic behavioro Good workability, easy making of jointso Accommodates the deformations of substrates and retards reflective cracking A good material for re-profiling purposes, maintenance works and local repairs

Yet high friction between larger aggregates once compacted GE can also be used for re-strengthening purposes

Full coating of larger aggregates is not ensured GE needs to be protected from climate and traffic (surface treatment, wearing course)



3. GRAVE-EMULSION (GE) – Main formulation parameters

Two main types (French standard XP P98-121)o Type R (Re-profiling) - 0/6 or 0/10

- Residual bitumen content : 4.2% – 4.5%- Thickness range : 0 to 8 cm

o Type S (Structuring)- 0/10 or 0/14 (0/20)- Residual bitumen content : 3.8% – 4.2%

- Thickness range : 8 to 15 cm Composition

o Sand content between 30 and 50%, fines between 6 and 8%o Cleanliness (no clay) is an essential requisiteo Use of RAP (even at high percentages) is possibleo Slow-setting bitumen emulsion (60 or 65% bitumen – 70/100 or 160/220 Pen.)o Total water content at about 7%



3. GRAVE-EMULSION (GE) – Fields of use (1/3)

New constructiono Type S material in base layers or binder courseo A strong subgrade is required to ensure efficient compaction

Ideal = unbound gravel (also ensures drainage of GE layer)

Specific application : prevention of reflective cracking on top of hydraulic layero High proportion of sand (> 40%) – 160/220 bitumen




Maintenance works and local repair – Type R materialo GE offer a particular economical and flexible solutiono Flexibility may be further enhanced by ensuring the GE material a certain storability




Upgrading and widening of existing roads – Type R materialo Restoring profiles and adapting roads to increasing traffic



3. GRAVE-EMULSION (GE) – Use of flux-oils

Advantages and drawbackso Improves the wetting of aggregates, workability and storabilityo Has of course a negative impact on short term mechanical properties

Type S materialso Only a “processing aid” - Maximum amount ≤ 2% (vs. emulsion)o “Storability” limited to 1 or 2 days

Type R materialso At high amounts, allows GE to be stockpiled and used for several weeks to monthso Use to be restricted for local repairs (potholes) and very low to low trafficked roads

HSE considerationso Strong incentive to switch from “mineral” flux oils to “vegetal” flux oilso But “hardening” is slower experience needs to be built-up !



3. GRAVE-EMULSION (GE) – Manufacturing

Stationary or mobile mixing unitso May be very simple (adaptation of mixing unit used for hydraulically bound materials)o Usually two-shaft paddle-mixero Plants tend to get more and more

sophisticated (development of EAC)

- Different streams for aggregatesand sand

- Multiple and adjustable feeding points for the emulsion(s)



3. GRAVE-EMULSION (GE) – Laying

Various equipments are possible depending on the application

o Gradero Pavero Fast paver

Bond coato Generally not necessary for Type R application (high amount of residual binder)o Recommended for Type S applications at low residual binder content



Fast paver (re-profiling)

4. EMULSION ASPHALT CONCRETE (EAC) – The challenge



Requirementso Continuously graded mixes for wearing courseso Resistance to water and traffic requests full aggregate coatingo Targeted residual binder contents are generally between 5.5% and 6%

The challenge : Ensure proper coating while maintaining sufficient workability o Breaking process of the emulsion

- Too slow : improper coating, water run-off during hauling- Too fast : formation of lumps, insufficient workability

o Adjustment parameters at hand- Formulation of the emulsion (in relation to aggregate)- Mixing process and equipments- Specific processes to improve workability- Many patents !

4. EMULSION ASPHALT CONCRETE (EAC) – Main formulation parameters



Typical formulationso Continuous grading 0/10 - Grading curves similar to those of GE o Sand between 25 and 35% - Fines around 7% o Residual bitumen (70/100 or 160/220) content is defined in relation to aggregate

specific surface area (French standard NF P 98-139) values close to 6% Mineral fractionso Aggregates must be suitable for wearing courseso Cleanliness (no clay) is an essential requisiteo Use of RAP (even at high percentages) is possible

Emulsion (Usually a 60% cationic slow-setting emulsion)o Formulation to be established in relation to aggregates and specific behaviour

requirements

4. EMULSION ASPHALT CONCRETE (EAC) – Emulsion and mix design



Cold mixes behave differently from hot mixeso Material is evolutive and its behaviour changes during the breaking process of the

emulsion and the progressive elimination of the watero Achievable initial void contents are higher than for hot mixes (but differently structured)o Conventional hot mix design procedures are inadequate Emulsion and mix design procedures must address these specific issueso Quality of coating (representative laboratory mixing procedures)o Workability and compacting abilityo Manufacturing of representative laboratory test samples (void contents)o Mechanical properties after ad-hoc accelerated curing procedures

This has triggered : Development of in-house design and evaluation procedures

Intensive and still on-going research (e.g. at USIRF)

4. EMULSION ASPHALT CONCRETE (EAC) – Mixing processes (1/5)

“One-step” processo Simplest equipment - Least expensive o But only possible with a limited number of aggregates



EMULSION

0/D

EAU EMULSION

0/D

EAU EmulsionWater


Use of a pre-coated sand (0/d) fractiono Sand to be pre-coated (emulsion or hot) in a separate processo Two separate aggregate feeders on the mixing plant



Emulsion Pre-coated 0/dd/D

Emulsion

0/d traité + d/D

Emulsion

0/d traité + d/D


Use of a pre-treated sand (0/d) fractiono Sand is pre-treated with a chemical (aqueous phase) to control its reactivityo Two possible ways to introduce the pre-treated 0/d fraction



Emulsion

treated 0/d + d/D Emulsion

0/d traitéd/D

Emulsion

0/d traitéd/D

treated 0/d

d/D

Emulsion


Use of a pre-coated aggregate (d/D) fractiono d/D fraction to be pre-coated (emulsion or hot) in a separate processo d/D may also be taken as screened RAP materialo 0/d and pre-coated d/D may be introduced simultaneously



Emulsion

0/d + d/D pré enrobé

Eau

0/d + Pre-coated d/D

Water Emulsion


Sequenced coatingo Two separate aggregate feederso Two separate emulsion inlets (same or different emulsions)o Most sophisticated equipment but offers a maximum flexibility



0/dd/D

Emulsion

d/D o/d

Eau

Emulsion

Water

4. EMULSION ASPHALT CONCRETE (EAC) – Specific processes to improve workability (1/2)

Semi-cold processes The final mix is “warmed-up” (40°C to 60°C above ambient)

o Use of the heat accumulated in hot pre-coated 0/d or d/D fractions

o Warming-up of the final mix(dedicated drum mixer)

o Mix has to be used immediatelyo Better homogeneity of binder filmo Improved compaction



Drum-mix reheating unit

4. EMULSION ASPHALT CONCRETE (EAC) – Specific processes to improve workability (2/2)

On-site manufacturing processeso Mobile mixing plant close to job-siteo Mobile equipment trains by which supplied materials are successively mixed and

fed to a paving screeno Mays also be used for GE



Mobile mixing and laying train

4. EMULSION ASPHALT CONCRETE (EAC) – Application (1/2)

Ideal for the maintenance of low to medium trafficked roado Usual thickness ranges from 3 to 5 cm, sometimes 2 to 3cm

(thicker lifts of 5 to 8cm are more seldom) o Bond coat is requiredo Due to its flexibility, EAC is well suited for the overlay of deformed pavements.

being directly usable as a wearing course, the re-profiling ability of EAC makes it an economical alternative to two-layer systems (e.g. reprofiling with

hot mix or GE + wearing course)



4. EMULSION ASPHALT CONCRETE (EAC) – Application (2/2)

Pavingo Done with conventional paverso Practice has however to be adapted to the particular behaviour of the material

(high internal friction)

Compactingo Usually steel rollerso Vibration has to be kept to a minimum

(risk of surface cracks)o Still a matter of trial and error



5. CONCLUSION – FUTURE PERSPECTIVES (1/2)



GE and EAC are still far from their full potential volume of useo 40 Mio tons hot mix, ~ 1.5 Mio tons GE, ~ 0.4 Mio tons EACo Cold techniques often restricted to areas where hot mix plants are scarceo The need to acquire specific know-how acts as a brake for wider development But circumstances are more favorable than evero Strive for safe and environmentally friendly techniqueso Growing awareness of the importance of Pavement Preservationo Significant technical progress has been made

Grave-Emulsion is now a proven technique Specific behavior of cold mixes is now well understood Formulation and evaluation methods have been significantly improved Improved mixing procedures and equipments are now available

5. CONCLUSION – FUTURE PERSPECTIVES (2/2)



The future : SUPER – GE ? o For the maintenance of slow to medium traffic roads, targeting the composition (in

particular the high binder content) and performance of hot mixes for EAC may not be necessary

o Improved emulsion design and enhanced mixing techniques allow GE to be formulated at higher binder contents, which makes them suitable as wearing course materials.

RATHER THAN AIMING AT A HOT MIX EQUIVALENT, AN “OPTIMIZED” GRAVE-EMULSION MAY BE THE TRUE FUTURE FOR EMULSIFIED ASPHALT CONCRETE

6. ACKNOWLEDGEMENTS / FURTHER INFORMATION

My acknowledgements go to the members of the USIRF Task Groups dedicated to the development and promotion of cold mix technologies, whose documents and advice helped me in making this overview. SFERB publication, 2008 : Bitumen emulsions

Related presentations at the 2012 ISAET Symposiumo J.P. Serfass- Emulsified Asphalt Mixes : Common Points, Advantages, Particularities, Drawbacks- Emulsion Asphalt Mixes : Proposed Mix Design Method & Performance-Based Specifications o F. Delfosse- Emulsified Asphalt Mixes : Grave-Emulsions Assessment and Design o A. Belkahia- Emulsified Asphalt Mixes : Emulsified Asphalt Concrete Assessment and Design



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Thank You for your attention

isaet 2012 - emulsified asphalt mixes by bernard eckmann

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