ISAET 2012 - Emulsified Asphalt Mixes by Bernard Eckmann

2012 International Symposium on Asphalt Emulsion Technology

EMULSIFIED ASPHALT MIXES
OVERVIEW OF THE EMULSIFIED ASPHALT MIXES IN FRANCE

B. Eckmann, Technical Department, EUROVIA (France)

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) products
o Formulation
o Properties
o Field of application
o 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 phase
o Aggregates are allowed to be not completely coated

Partially coated aggregate

Binder-rich mortar



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

 Plastic behavior
o Good workability, easy making of joints
o 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 requisite
o Use of RAP (even at high percentages) is possible
o 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 construction
o Type S material in base layers or binder course
o 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 layer
o High proportion of sand (> 40%) – 160/220 bitumen




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




 Upgrading and widening of existing roads – Type R material
o Restoring profiles and adapting roads to increasing traffic



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

 Advantages and drawbacks
o Improves the wetting of aggregates, workability and storability
o Has of course a negative impact on short term mechanical properties
 Type S materials
o Only a “processing aid” - Maximum amount ≤ 2% (vs. emulsion)
o “Storability” limited to 1 or 2 days
 Type R materials
o At high amounts, allows GE to be stockpiled and used for several weeks to months
o Use to be restricted for local repairs (potholes) and very low to low trafficked roads
 HSE considerations
o Strong incentive to switch from “mineral” flux oils to “vegetal” flux oils
o But “hardening” is slower  experience needs to be built-up !



3. GRAVE-EMULSION (GE) – Manufacturing

 Stationary or mobile mixing units
o May be very simple (adaptation of mixing unit used for hydraulically bound materials)
o Usually two-shaft paddle-mixer
o Plants tend to get more and more
sophisticated (development of EAC)
- Different streams for aggregates
and sand
- Multiple and adjustable
feeding points for the
emulsion(s)



3. GRAVE-EMULSION (GE) – Laying

 Various equipments are possible
depending on the application

o Grader
o Paver
o Fast paver

Fast paver (re-profiling)
 Bond coat
o Generally not necessary for Type R application (high amount of residual binder)
o Recommended for Type S applications at low residual binder content



4. EMULSION ASPHALT CONCRETE (EAC) – The challenge

 Requirements
o Continuously graded mixes for wearing courses
o Resistance to water and traffic requests full aggregate coating
o 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 formulations
o 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 fractions
o Aggregates must be suitable for wearing courses
o Cleanliness (no clay) is an essential requisite
o 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 mixes
o Material is evolutive and its behaviour changes during the breaking process of the
emulsion and the progressive elimination of the water
o 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 issues
o Quality of coating (representative laboratory mixing procedures)
o Workability and compacting ability
o 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” process
o Simplest equipment - Least expensive
o But only possible with a limited number of aggregates

0/D

Water Emulsion
EMULSION
EAU




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

d/D Emulsion Pre-coated 0/d




 Use of a pre-treated sand (0/d) fraction
o Sand is pre-treated with a chemical (aqueous phase) to control its reactivity
o Two possible ways to introduce the pre-treated 0/d fraction
Emulsion
Emulsion
treated 0/d d/D
0/d traité + + d/D
treated
0/d
d/D
d/D
Emulsion
Emulsion 0/d
traité




 Use of a pre-coated aggregate (d/D) fraction
o d/D fraction to be pre-coated (emulsion or hot) in a separate process
o d/D may also be taken as screened RAP material
o 0/d and pre-coated d/D may be introduced simultaneously
0/d++ Pre-coated d/D
0/d d/D pré enrobé

Water Emulsion
Eau Emulsion




 Sequenced coating
o Two separate aggregate feeders
o Two separate emulsion inlets (same or different emulsions)
o Most sophisticated equipment but offers a maximum flexibility
d/D o/d

d/D 0/d

WaterEau
Emulsion
Emulsion
Additif



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 immediately
o Better homogeneity of binder film
o Improved compaction
Drum-mix reheating unit



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

 On-site manufacturing processes
o Mobile mixing plant close to job-site
o Mobile equipment trains by which supplied materials are successively mixed and
fed to a paving screen
o 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 road
o 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 required
o 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)

 Paving
o Done with conventional pavers
o Practice has however to be adapted to the particular behaviour of the material
(high internal friction)

 Compacting
o Usually steel rollers
o 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 use
o 40 Mio tons hot mix, ~ 1.5 Mio tons GE, ~ 0.4 Mio tons EAC
o Cold techniques often restricted to areas where hot mix plants are scarce
o The need to acquire specific know-how acts as a brake for wider development

 But circumstances are more favorable than ever
o Strive for safe and environmentally friendly techniques
o Growing awareness of the importance of Pavement Preservation
o 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



Thank You for your attention
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 Symposium
o 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

bernard.eckmann@eurovia.com

ISAET 2012 - Emulsified Asphalt Mixes by Bernard Eckmann

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