Lab and field eveluation of recycled cold mix

Dissertation report on

“LABORATORY AND FIELD EVALUATION OF
RECYCLED COLD MIXES”
Submitted in partial fulfillment for award of the degree of

MASTER OF TECHNOLOGY
In
TRANSPORTATION ENGINEERING
(2004-2006)

Submitted by: G.NARENDRA GOUD
Under the guidance of

DR. SUNIL BOSE SHRI ARUN GAUR
Head, Lecturer
Flexible Pavements Division, Department of Civil Engineering
CRRI-New Delhi MNIT-Jaipur

DEPARTMENT OF CIVIL ENGINEERING
MALAVIYA NATIONAL INSTITUTE OF TECHNOLOGY
(DEEMED UNIVERSITY)
JAIPUR (RAJASTHAN)-302017

Laboratory and Field Evaluation of Recycled Cold Mixes I

CERTIFICATE

This is to certify that the Dissertation report entitled “LABORATORY AND
FIELD EVALUATION OF RECYCLED COLD MIXES” being submitted by
Mr. G. NARENDRA GOUD (College ID -046126) to the Department of civil
engineering, Malaviya National Institute of Technology-Jaipur, in partial fulfillment
for the award of Master of Technology in Transportation Engineering is a bona fide
work carried out by him under our guidance and supervision.

The contents of this dissertation, in full or in parts, have not been submitted to any
other institute or university for the award of any degree or diploma.

Place: New Delhi
Date: / 6/ 2006

(Dr. SUNIL BOSE) (Shri ARUN GAUR)
Head, Lecturer
Flexible Pavements Division, Department of Civil Engineering
CRRI-New Delhi MNIT-Jaipur

Laboratory and Field Evaluation of Recycled Cold Mixes II

ACKNOLEDGEMENTS

I would like to express my sincere gratitude to Dr. P.K. Nanda, Director, Central Road Research

Institute, New Delhi for permitting me to carryout my dissertation work in Flexible Pavements

Division, CRRI.

It is most pleasant to express hearty gratitude to my external guide Dr Sunil Bose, Head flexible

pavements division-CRRI, who has given me the opportunity and under whose supervision I was

able to do my dissertation work. Words can not do much justice to the guidance and help given by

him.

I sincerely express my deep gratitude to my internal guide Shri. Arun Gaur, Lecturer, Department

of Civil Engineering and Shri. Girish shrma for their guidance and support.

I am very much thankful to Shri. Subhash Niyogi, Managing Director of Wirtgen India Private

Limited, for providing me all the facilities in carrying out the study. I am grateful to all the

employees of Wirtgen India Private Limited-Bangalore whoever helped me during my association

with the firm. And also I’m very thankful to Devendhar Singh Bisth, Quality control engineer,

Nagarjuna Construction Company (NCC) Pvt. Ltd. for aiding me the laboratory facilities at their

project site Bidadi-Bangalore.

Laboratory and Field Evaluation of Recycled Cold Mixes III

My Hearty Gratefulness and thanks to Dr. Pawan Saluja, Shri. Gajender Kumar, Shri Manoj

Shukla, Dr. Sangitha and CRRI-Flexible Pavements Division staff for their encouragement,

technical guidance and support during my laboratory study.

I would like to thank Dr Rohit Goyal, Head Department of Civil Engineering, Malaviya National

Institute of Technology, Jaipur. for giving me the permission to do my dissertation work at CRRI.

I would like to thank Dr. Krishna Murthy, Head Department of Civil Engineering, Bangalore

University who has accepted immediately to conduct BBD study on the test track.

My special thanks to Shri. Pawan Kalla, Lecturer Department of Civil Engineering, Malaviya

National Institute of Technology, Jaipur and Shri. Sridhar Raju, Scientist, CRRI. who

encouraged and supported me to do my dissertation work at CRRI-New Delhi.

Last but never the least; I would like to state my deep gratitude for all the support given

required from time to time, by my parents and all my friends.

Once again I thank one and all who have helped me directly or indirectly in completion of

my dissertation work.

(G. Narendra Goud)

Laboratory and Field Evaluation of Recycled Cold Mixes IV

ABSTRACT

In the dense populated cities like Delhi, where environmental pollution and Land fill problems are
of prime concerns in the recent years. In rapid developing countries like India, where conservation
and optimum utilization of the road building materials specially petroleum and mineral products
are an important issue. There is an immediate attention requirement towards the development and
implementation of Ecofriendly and cost effective pavement construction technologies. Through
application of these technologies the efficient use of existing and waste materials can be made
with out creating problems to the environment and at the same time meeting the quality
requirements of the pavements.

Advances in technology and techniques in the in recent years have made cold recycling an
increasingly popular and cost-effective pavement construction and maintenance technique. In the
present study an effort is made to study the laboratory and field behaviour of recycled cold mixes
with binders as an emulsion and foamed bitumen. The Marshall specimens were cast using
emulsion and foamed bitumen in combination with different types of fillers such as cement, lime
and fly-ash. The specimens were tested for density, Indirect Tensile Strength, Resilient modulus
and dynamic creep. Benkelman Beam deflection study was carried out on the pavement
constructed with recycled foamed bituminous mix after a period of three months from construction
and field cores were cut from the pavement and were investigated in the Laboratory. It was found
that the pavement constructed with foamed bitumen treated RAP was structurally sound and cores
cut from that pavement have shown higher ITS and MR values when compared with Laboratory
cast cores but they shown less creep stiffness and densities. In comparison with emulsion treated
RAP, foamed bitumen treated RAP shown higher density, ITS, MR and creep stiffness with same
aggregate and gradation.

Laboratory and Field Evaluation of Recycled Cold Mixes V

CONTENTS
S.NO. TITLE Pg NO

1. INTRODUCTION...................................................................................................................... 1
1.1 General ................................................................................................................................. 1
1.2 Objectives............................................................................................................................. 2
1.3 Scope of Work ..................................................................................................................... 2
1.4 Methodology Adopted ......................................................................................................... 2
2. LITERATURE REVIEW .......................................................................................................... 3
2.1 Why Milling? ....................................................................................................................... 3
2.2 Why Recycling?................................................................................................................... 3
2.3 Methods of Pavement Recycling ......................................................................................... 4
2.4 Candidates for Recycling ..................................................................................................... 5
2.5 Advantages of Cold Recycling ............................................................................................ 6
2.6 Bitumen Emulsion................................................................................................................ 7
2.7 Bitumen Emulsion Classification......................................................................................... 8
2.8 Recycling With Bitumen Emulsion ..................................................................................... 9
2.9 Foamed Bitumen ................................................................................................................ 12
2.10 Characterization of Foamed Bitumen .............................................................................. 13
2.11 Factors influencing foam properties ................................................................................ 14
2.12 Dispersion of foamed bitumen......................................................................................... 16
2.13 Material suitability for foamed bitumen treatment .......................................................... 17
2.14 Recycling with foamed bitumen ...................................................................................... 19
2.15 The benefits of foamed bitumen stabilisation .................................................................. 26
2.16 Case studies...................................................................................................................... 29
Experience in India: ................................................................................................................. 29
2.16.1 Emulsion Cold Recycling Rehabilitation Project-Hyderabad ...................................... 29
2.16.2 Foam bitumen cold recycling rehabilitation project-Bangalore ................................... 35
Experience in abroad:............................................................................................................... 40
2.16.3 Emulsion Cold Recycling Rehabilitation Project. Citizen Court, Toronto, June 2003 40

Laboratory and Field Evaluation of Recycled Cold Mixes VI

2.16.4 Saudi Arabia – A desert road for heavy traffic ............................................................. 45
2.16.5 In-Plant recycling using milled asphalt bound with foamed bitumen .......................... 47
3. LABORATORY AND FIELD STUDY ...................................................................................... 55
3.1 RAP and Mineral Aggregate Evaluation ........................................................................... 55
3.2 Foamed Bitumen Characterization..................................................................................... 55
3.3 Emulsion Testing ............................................................................................................... 59
3.4 Mineral Aggregate Proportions.......................................................................................... 59
3.5 OMC Determination for Foamed Bitumen Treatment....................................................... 64
3.6 OFC Determination for Emulsion Treatment .................................................................... 65
3.7 Recycled Cold Mix Preparation with Foamed Bitumen .................................................... 66
3.8 Recycled Cold Mix Preparation with Emulsion ................................................................ 69
3.9 Foamed bitumen and Bitumen Emulsion treated RAP Specimen testing.......................... 70
3.10 Benkelman Beam Deflection testing................................................................................ 76
4. RESULTS AND ANALYSIS ..................................................................................................... 77
4.1 Results of Foamed Bitumen Treated RAP Marshall Specimens ....................................... 77
4.2 Results of Emulsified Bitumen Treated RAP Marshall Specimens................................... 85
4.3 Field and Laboratory Core Comparison............................................................................. 89
4.4 Dynamic Creep Test Results Analysis............................................................................... 90
5. CONCLUSIONS AND RECOMMENDATIONS ...................................................................... 92
6. APPENDICES .......................................................................................................................... 93
Appendix 1: Material Sampling and blending ......................................................................... 93
Appendix 2: Mix Design Procedure for Bitumen Stabilised Materials ................................... 95
Appendix 3: Strength Test Procedures................................................................................... 105
7. REFERENCES....................................................................................................................... 108

Laboratory and Field Evaluation of Recycled Cold Mixes VII

LIST OF FIGURES

Figure 2.1: Example of fluid considerations for a bitumen emulsion stabilised material 10
Figure 2.2: Schematic diagram of foamed bitumen production 12
Figure 2.3: Bitumen Foam characterization 14
Figure 2.4: Foamed bitumen dispersion and binding in the treated mix 17
Figure 2.5: Material gradation envelops 18
Figure 2.6: A view of recycling process progress in Hyderabad 31
Figure 2.7: Aggregate Spread over the layer to be recycled to correct the Gradation 31
Figure 2.8: Recycling crew in action 32
Figure 2.9: Recycled layer after pre compaction 32
Figure 2.10: Compacting the recycled layer 33
Figure 2.11: Tack coat application over the recycled and compacted layer 33
Figure 2.12: Finished surface of the recycled layer 34
Figure 2.13: Loader used to load the materials in to the mobile plant 37
Figure 2.14: Cement and hot bitumen supplied to the plant 37
Figure 2.15: Recycled material being discharged in to the dumper 38
Figure 2.16: Recycled foamix being dumped in to the paver hopper 38
Figure 2.17: Initial compaction with vibrator roller 39
Figure 2.18: Final compaction with pneumatic tyred roller 39
Figure 2.19: Recycling option used 42
Figure 2.20: Emulsion tanker and recycler 42
Figure 2.21: Pre-compacted surface after 1st pass 43
Figure 2.22: Cold milling from kerb outwards 44
Figure 2.23: Pre-compacted surface after 2nd pass 45
Figure 2.24: Recycling of Shaybah Access road 46
Figure2.25: The Hartl Powercrusher PC 1270 I Impact crusher being used to crush the RAP
material 50
Figure2.26: The Wirtgen KMA 200 cold mixing plant utilized to dose and mix the binding
agents and water with the RAP 50

Laboratory and Field Evaluation of Recycled Cold Mixes VIII

Figure 2.27: Vogele 1800 paving the foamed bitumen treated base material directly onto the
road as an overlay 51
Figure 2.28: Compaction done with HAMM HD O70V double drum Oscillation /
Vibration roller and HAMM GRW 18 pneumatic tyred roller 51
Figure2.29: The road surface being moistened with water during final compaction and
just before traffic is allowed onto the base course 52
Figure2.30: The longitudinal joint being moistened before paving of the second road-width52
Figure 2.31: Paving of the second road width and traffic on the freshly compacted material.
This layer was kept moist for the first couple of hours for curing purposes 53
Figure2.32: The finished cold recycled base course after being trafficked for several days 53
Figure2.33: The Tack coat applied by a hand sprayer on one half of the base course 54
Figure2.34: Paving and compaction of the 4 cm asphalt wearing course 55
Figure3.1: WLB 10- Wirtgen foamed bitumen lab kit 57
Figure3.2: Air pressure Influence on expansion ratio and half time of Foamed bitumen 58
Figure3.3: Bitumen temperature Influence on expansion ratio and half time of Foamed
bitumen 58
Figure3.4: Bitumen water content Influence on expansion ratio and half life time of Foamed
bitumen 59
Figure3.5: option1 gradation curves 62
Figure3. 8: option4 gradation curves 63
Figure3.9: samples of separated RAP and stone dust 64
Figure3.10: OMC determination 64
Figure3.11: OFC determination 65
Figure3.12: Mineral aggregates used in the study 66
Figure3.13: WLB10 laboratory plant used to produce foamed bitumen 66
Figure3.14: Pug-mill type mixer used to prepare foamix 67
Figure3.15: Hobart mixer used to prepare emulsion mixture 69
Figure3.16: Indirect Tensile Strength Testing Schematic diagram 70
Figure3.17: Specimen setup of Indirect Tension Test for Resilient Modulus 71

Laboratory and Field Evaluation of Recycled Cold Mixes IX

Figure3.18: Specimen setup of dynamic creep testing 71
Figure3.19: Benkelman Beam rebound deflection variation with distance 76
Figure 7.1 Determination of optimum foaming water content 100

LIST OF TABLES
Table2. 1: The major uses of bitumen emulsion 07
Table2. 2: Bitumen emulsion classification and their recommended application.
(IS 8887-2004) 08
Table2. 3: Foamed bitumen dispersion (ability to mix) 20
Table2. 4: Typical foamed bitumen contents relative to key aggregate fractions 21
Table2. 5: Tentative binder and additional treatment requirements 22
Table2.6: Comparison between different types of bitumen applications 28
Table3. 1: Sieve analysis of pulverized and air-dried RAP 55
Table3. 2: Sieve analysis of Stone Dust 55
Table3. 3: Air pressure Influence on expansion ratio and half time of Foamed bitumen 57
Table3. 4: Bitumen temperature Influence on expansion ratio and half time of Foamed
bitumen 58
Table3. 5: Study of Bitumen water content Influence on expansion ratio and half life time
of Foamed bitumen 58
Table3. 6: Tests on Emulsion 59
Table3. 7: Different options of aggregate proportions 60
Table3. 8: Option1 Material proportions 60
Table3.9: Option2 Material proportions 60
Table 3.12: Material calculations for foamix preparation 68
Table 3.13 Foamed bitumen Specimen test results 72
Table 3.14 Bitumen Emulsion Specimen test results 74
Table3.15: Dynamic Creep Test results 75
Table3.16: Deflection data (LHS, towards Karnataka cold Storage Pvt. ltd) 76

Laboratory and Field Evaluation of Recycled Cold Mixes X

Table3.17: Deflection data (RHS, towards Karnataka cold Storage Pvt. ltd) 76
Table4.1: Maximum bulk density values from the Graphs 4.1(a, b, c) 77
Table 4.2: Maximum Resilient modulus (MR) values from the Graphs 4.2(a, b) 80
Table4.3: Maximum Resilient modulus (MR) values from the Graphs 4.3 (a, b) 81
Table4.4: Maximum Resilient modulus (MR) values from the Graphs 5.6(a, b) 82
Table 4.5: Maximum Dry Indirect Tensile Strength (ITS) values from the Graphs 4.5 (a, b, c) 83
Table 4.6: Maximum soaked Indirect Tensile Strength (ITS) values 83
Table4. 7: Maximum bulk density values From the Graphs 4.6 (a, b) 85
Table4. 8: Maximum Resilient Modulus values from the Graphs 4.7 (a, b) 86
Table 4. 9: Maximum Dry and Soaked Indirect Tensile Strength (ITS) values from the Graphs 4.8
(a, b) and 4.9 (a, b) 87

LIST OF GRAPHS

Graph4. 1:( a, b, c) Variation of bulk density with foamed bitumen and filler 78
Graph4.2 :( a, b) Variation of Resilient Modulus with foamed bitumen and Cement 80
Graph4.3 :( a, b) Variation of Resilient Modulus with foamed bitumen and Lime 81
Graph4.4 :( a, b) Variation of Resilient Modulus with foamed bitumen and Fly-ash 82
Graph4.5: (a, b, c) Variation of dry ITS with foamed bitumen 84
Graph4.6 :( a ,b) Variation of bulk density with Bitumen Emulsion 85
Graph4.7 :( a, b) Variation of Resilient Modulus with Bitumen Emulsion 86
Graph4.8: (a, b) Variation of ITS with Bitumen Emulsion and Cement 88
Graph4.9 :( a, b) Variation of ITS with Bitumen Emulsion and lime 88
Graph4.10 :( a, b, c) Variation of Resilient Modulus, Bulk density and ITS in
different cores 89
Graph4.12 :( a, b, c) Variation of Accumulated axial strain with Number of cycles 90
Graph4.11 :( a, b) Variation of Accumulated axial strain with Number of cycles 91

Laboratory and Field Evaluation of Recycled Cold Mixes XI

_________________________________________CHAPTER 1
1. INTRODUCTION
1.1 General

In the dense populated cities like Delhi, where environmental pollution and Land fill problems are
of prime concerns in the recent years. In rapid developing countries like India, where conservation
and optimum utilization of the road building materials specially petroleum and mineral products
and energy are an important issues. The rehabilitation and up gradation of existing badly
distressed Pavements due to rapidly growing heavy vehicular traffic are attracting the
concentration. There is an immediate attention requirement towards the development and
implementation of Ecofriendly pavement construction technologies. Through application of these
technologies the efficient use of existing and waste materials can be made with out creating
problems to the environment and at the same time meeting the quality requirements of the
pavements.

Advances in technology and techniques in the in recent years have made cold recycling an
increasingly popular and cost-effective pavement construction and maintenance technique. It has
been proved in abroad that cold recycling with emulsion or foamed bitumen is one of the best
alternatives to be considered as a rehabilitation option. Cold recycling technology can be an option
which has the potential to address the above mentioned issues.

In the present study an effort is made to study the laboratory and field behaviour of recycled cold
mixes with binders as an emulsion and foamed bitumen. The Marshall specimens were cast using
emulsion and foamed bitumen in combination with different types of fillers such as cement, lime
and fly-ash. The specimens were tested for density, Indirect Tensile Strength, Resilient modulus
and dynamic creep. Benkelman Beam deflection study was carried out on the pavement
constructed with recycled foamed bituminous mix after a period of three months from construction
and field cores were cut from the pavement and were investigated in the Laboratory.

Laboratory and Field Evaluation of Recycled Cold Mixes 1

1.2 Objectives
• To study the suitability of cementitious and bituminous agents (Emulsion and Foamed
bitumen) for cold recycling
• To determine optimum content of stabilizing agent
• To study the performance of stabilized mix

1.3 Scope of Work
In the present study stabilizing agents viz. cementitious and bituminous was investigated for its
use with Recycled Asphalt Pavement (RAP) material. The effect of different stabilizing agents and
their dosage on density, indirect tensile strength (ITS) and other performance parameters of
stabilized mix were studied.

1.4 Methodology Adopted
Determination of foaming properties of bitumen viz. expansion ratio and half life using
Wirtgen WLB 10 foamed bitumen laboratory unit
Preparation of samples using different combinations of granular/RAP material and
stabilizing agents
Preparation of Samples of different combinations of cement, lime, fly-ash, emulsion and
foamed bitumen and testing for density and indirect tensile strength (ITS) to determine
optimum content of stabilizing agent
Determination of Stiffness of bitumen-stabilized material by subjecting 100 mm diameter
Marshall Specimen to repeated load testing
Study of Performance of test track laid with recycled asphalt pavement by evaluating cores
from the existing cold recycled pavement and testing for performance characteristics
Determination of structural adequacy of the Recycled foamed bitumen test track by
Benkelman beam deflection study


_________________________________________CHAPTER 2
2. LITERATURE REVIEW
2.1 Why Milling?
Milling is the process of cutting away material by feeding a work piece past a rotating multiple
tooth cutter. It can be carried out when the pavement condition is in COLD or HOT. Cold milling
is considered to be more economical, ecofriendly in nature and can be done to pavement full
depth.
Earlier roads were designed for less traffic and lighter vehicle weights than found today. Many
roads are being distorted and failing prematurely as a result. Reestablishing a uniform surface is
essential if these roads are to be properly repaired. Milling provides a uniform surface for the
placement of new pavement. If rutted roads are overlaid as it is, insufficient material is placed in
the rutted area, producing low density in the areas of the ruts. By milling to a flat surface, recycled
material is created, the ruts are eliminated, and the new pavement will have a uniform density
across the entire lane. Milling can reestablish the proper road grade and slope and eliminate high
spots and ruts. Many times, milling can reduce or even eliminate reflective cracking. Better
leveling can be achieved by milling than by applying a leveling course of asphalt. Furthermore,
considerable savings result. Other very significant advantages are gained by milling and inlaying
on highway work are Shoulders do not have to be raised, Guard rails do not have to be raised
because the road elevation remains the same. Milling also provides utility accesses (i.e. drain
gullies, man holes, etc) to remain same. Bridge clearances remain the same, so clearance signs do
not have to be changed.

2.2 Why Recycling?
Recycling:-The reuse, usually after some processing, of a material that has already served its first
intended purpose.
The reasons for, and advantages from, Recycled Asphalt (RA) being put back in to pavements can
be summarized in the fallowing simple points
• The use of already existing materials, the elimination of disposal problems and
conservation of natural resources (aggregates and petroleum products).


• Major energy savings, including those related to avoiding processing of additional virgin
material and the potential for reduced haulage of materials with associated reduction in
energy emissions and congestion.
• A cost reduction with respect to other conventional methods of restoring former properties
of the road.
Furthermore, adding RA also provides:
• The opportunity to modify the grading of the aggregate and/or the properties of the binder
in the existing asphalt in order to improve the properties of in-situ mixture.
• The opportunity to correct the profile and/or the cross fall of the pavement and improve the
smoothness and ride quality.[1]

2.3 Methods of Pavement Recycling
Pavement may be recycled in-place or in-plant depending on various factors such as availability of
equipment, existing material quality and requirement of the quality control over the treated
material.
An in-situ or in-place recycling process involves a train of machines planing out, and then
immediately processing, the material and relaying it without removing it from site. In-situ
recycling is usually preferred because it is less costly (with the elimination of costs associated the
stockpiling, handling, maintaining an inventory and long distance hauling of the reclaimed
material) and because it causes less disruption to the traffic.
An off-site or in-plant recycling process involves processing the material in a central plant (often
far from the works location) or in a mobile recycling plant just near the works location.
The Asphalt Recycling and Reclaiming Association (ARRA) recognizes five types of asphalt
pavement recycling:
i. Cold planing
ii. Hot recycling
iii. Hot in-place recycling
iv. Cold recycling and
v. Full-Depth Reclamation
Cold planing:- The asphalt pavement is removed to a specified depth and the surface is restored to
a desired grade cross slope and free of humps, ruts and other imperfections. The pavement


removal or “milling” is completed with a self propelled rotary drum cold planing machine. The
Reclaimed Asphalt Pavement (RAP) is transferred to trucks after removal and stockpiled for hot or
cold recycling.
Hot recycling:-RAP is combined with new aggregate and asphalt cement and/or recycling agent to
produce Hot Mix Asphalt (HMA). Although batch type hot mix plants are used, drum plants
typically are used to produce the recycled mix. Most of the RAP is produced by cold planing but
also can be produced from pavement removal and crushing. The mix placement and compacting
equipment and procedures are those typical of HMA construction.
Hot In-place Recycling (HIPR): The HIPR is defined as a process to correct asphalt pavement
surface distress by softening the existing surface with heat, mechanically removing the pavement
surface, mixing the reclaimed asphalt with a recycling agent, possibly adding virgin asphalt and/or
aggregate, and relaying. A train of machines, working in succession, performs the recycling.
Cold Recycling:- Although cold recycling is performed using a stationary or mobile plant process,
the method most commonly used is Cold In-place Recycling (CIR). For CIR, the existing asphalt
pavement typically is processes to a depth of from 50 to 100mm. the pavement is pulverized and
the reclaimed material is mixed with an Emulsion or foamed bitumen, spread and compacted to
produce a base course. Cold recycled base courses require a new asphalt surface
Full Depth Reclamation (FDR):- With FDR, all of the pavement section, and in some cases a
predetermined amount of underlying material are mixed with asphalt emulsion or Foamed bitumen
to produce a stabilized base course. Base problems can be corrected with this construction. FDR
consists of six basic steps: pulverization, stabilizing agent and/or emulsion or Foamed bitumen
incorporation, spreading, compacting, shaping and placement of new asphalt surface. [2]

2.4 Candidates for Recycling
A candidate for recycling is usually an old asphalt pavement, from HMA to an aggregate base
with surface treatment. Candidate pavement will have severe cracking and disintegration, such as
pot holes. Frequently the poor condition is due to the pavement being too thin or weak for the
traffic and so it is being over stressed. Poor drainage can also accelerate the rate and amount of
pavement deterioration. All types of asphalt pavements can be recycled: low, medium and high
traffic volume highways, urban streets, airport taxi ways, runways and aprons, and parking lots.
[2]


2.5 Advantages of Cold Recycling
Cold recycling and full depth reclamation of asphalt pavements provide many environmental and
other advantages:
Energy is conserved as the construction is completed in-place/mobile plant and no fuel is
required for aggregate heating.
Reflective cracking can be controlled since it is normally reduced with CIR and eliminated
by Full Depth Reclamation
Pavement crown and cross slope can be improved or restored.
Pavement maintenance costs can be reduced by increasing Life Cycle Cost of the existing
materials since it is reclaimed.
Traffic can be allowed immediately after construction of the pavement and the obstructions
to the traffic are also nominal since the construction operation can be carried out safely.
Existing material can be used completely (100% usage) irrespective of material quality.


2.6 Bitumen Emulsion
Bitumen emulsions, used in road construction and maintenance, may be defined as a homogeneous
mixture of minute Bitumen droplets suspended in a continuous water phase. These types of
emulsions are usually termed oil-in-water (o/w) emulsions. Emulsions typically contain asphalt
cement, water, and emulsifying agent in the following approximate proportions: 65-70%, 30-35%,
and 2-3%, respectively. Their preparation involves the use of a high speed, high shear mechanical
device, such as a colloid mill. The colloid mill breaks down molten asphalt into minute droplets in
the presence of water and a chemical, surface-active emulsifier. The emulsifier imparts its
properties to the dispersed asphalt arid is most influential in maintaining stable asphalt droplet
suspension.
Advantages of emulsion:
The emulsions are more tolerant than penetration grade bitumens, of the presence of
dampness, although they should not be used in the presence of free water, on the road
surface or on aggregates.
Because emulsions are of relatively low viscous at normal temperatures, they eliminate the
need to heat the aggregates and binder, and thus they conserve energy.
Emulsions use reduces environmental pollution (especially because, unlike cutback
bitumen, they do not release harmful diluents in to the environment).
They can be used when the weather is relatively cold.
Table2. 10: The major uses of bitumen emulsion
Surface treatments Asphalt recycling Other applications
Fog sealing, Sand sealing, Cold in-place, Full depth, Hot Stabilization, Maintenance
Slurry sealing, Micro- in-place, Central plant patching, Tack coats, Prime
surfacing, Cape sealing coats, Dust palliatives, Crack
filling, Protective coatings


2.7 Bitumen Emulsion Classification
Bitumen emulsions are classified into three categories: anionic, cationic and nonionic. In practice
the first two types are more widely used in roadway construction and maintenance.
Emulsions are further classified on the basis of how quickly the bitumen droplets will coalesce.
The terms RS, MS, SS and QS have been adopted in this classification. They are relative terms
only and mean rapid setting, medium setting, slow setting and quick setting. The tendency to
coalesce is closely related to the speed with which an emulsion will become un-stable and break
after contacting the surface of aggregate. An RS emulsion has little or no ability to mix with an
aggregate, an MS emulsion is expected to mix with coarse but not fine aggregate, and SS and QS
emulsions are designed to mix with fine aggregate, with the QS expected to break more quickly
than the SS.
Emulsions are further identified by a series of numbers and letters related to viscosity of the
emulsions and hardness of the base bitumen. The letter “C” in front of the emulsion type denotes
cationic. The absence of “C” denotes anionic in American Society for Testing and Materials
(ASTM) and American Association of State Highway and Transportation Officials (AASHTO)
specifications.
The numbers in the classification indicate the relative viscosity of the emulsion. For example, an
MS-2 is more viscous than an MS-1. The “h” that fallows certain grades simply means that harder
base bitumen is used. An “s” means that softer base bitumen is used.
The “HF” preceding some of the anionic grades indicates high-float, as measured by the float test.
High float emulsions have a gel quality, imparted by the addition of certain chemicals, that permits
a thicker bitumen film on the aggregate particles and prevents drain off of bitumen from the
aggregate. These grades are primarily for cold and hot plant mixes, seal coats and road mixes.[6]
Table2. 11: Bitumen emulsion classification and their recommended application. (IS 8887-2004)
Emulsion Recommended application
type
RS-1 Tack coat applications.
RS-2 Surface dressing work.
Plant or road mixes with coarse aggregates minimum 80%, all of which is retained
MS
on 2.36mm IS Sieve, and also for surface dressing and penetration macadam.
SS-1 Fog seal, Crack sealing and Prime coat applications.
Plant or road mixes with graded and fine aggregates such as Cold mixes MSS,
SS-2
SDBC and slurry seal.


2.8 Recycling With Bitumen Emulsion
When recycling with bitumen emulsion the following points are important and need to be
addressed:
Mix design
As with any form of stabilisation, a proper mix design procedure should be followed to determine
the correct application rate required to meet the strength criteria. Each material requires its own
application rate of bitumen emulsion to achieve optimum or desired strength.
Formulation
Different emulsifiers and additives are used in varying proportions to “tailor” an emulsion for a
specific application. In addition to determining the amount of residual bitumen suspended in
water, such tailoring is aimed at controlling the conditions under which the bitumen breaks. Since
the type of material that is mixed with the emulsion has a major influence on stability (breaking-
time), it is important that the manufacturer be given a representative sample of the material that is
to be recycled. Details of any active filler to be added in conjunction with the bitumen emulsion
must also be supplied to allow the correct formulation to be developed and tested.
Handling
Bitumen emulsions are susceptible to temperature and pressure. The conditions that will promote
the bitumen to separate out of suspension (slowly as “flocculation”, or instantly as a “flash-break”)
must be clearly understood to prevent this from happening on the site. Likewise, the manufacturer
must know the conditions prevailing on site to allow the correct formulation, including the details
of all pumps that will be used for transferring the emulsion between tankers and for supplying the
spray bar on the recycler. Blending of anionic and cationic emulsions results in an instantaneous
break and blockage of pumps and pipes with viscous bitumen, for example. This can be prevented
by labeling and storing emulsions carefully and ensuring that distribution systems are clear of
residue from previous use.
Total fluid content concept
When working with bitumen emulsions, “Total Fluid Content” is used in place of Moisture
Content in defining the moisture/density relationship. Maximum density is achieved at the
Optimum Total Fluid Content (OTFC), which is the combined mass of moisture and bitumen
emulsion in the mix. Before breaking, bitumen emulsion is a fluid with a viscosity slightly higher


than that of water. Both the bitumen and water components of an emulsion act as a lubricant in
assisting compaction, so both must be included as fluids. This is illustrated in Figure 2-1.

Figure 2-1 Example of fluid considerations for a bitumen emulsion stabilised material

The example in Figure 2-1 shows the in-situ field moisture content as 2.5 % with 3.5 % bitumen
emulsion applied whilst recycling. The material has an OTFC of 7% under standard compaction.
An additional 1.0% of water may be added during recycling to bring the total fluid content to the
OTFC, or additional compactive effort applied to achieve maximum density. If the total fluid
content of the material approaches saturation level (as indicated by the zero air voids line), then
hydraulic pressures will develop under the roller causing the material to heave. When such
conditions arise it is impossible to compact the material. Where the in-situ field moisture content
is high (i.e. approaching the OTFC), the addition of bitumen emulsion can increase the total fluid
content beyond the saturation point. This situation cannot be addressed by reducing the amount of
bitumen emulsion added without compromising the quality of the stabilised product. The
temptation to add cement to the mix in order to “absorb the surplus moisture” should not be
considered since such a practice introduces rigidity and changes the nature of the product. High in-


situ moisture contents are best addressed by pre-pulverising the existing pavement thereby
exposing the material and allowing it to dry sufficiently before stabilising.
Processing time
No specific time limit is placed on working with bitumen emulsions other than the requirement of
completing all processing, compacting and finishing before the emulsion breaks. When emulsion
breaks, the bitumen comes out of suspension and the viscosity of the fluid increases significantly.
The individual particles of the recycled material will then be either coated, or semi-coated with a
thin film of cold, viscous bitumen, making it more difficult to compact. Compaction should
therefore be completed before or during the emulsion breaking process.
Density
The compaction should always aim to achieve the maximum density possible under the conditions
prevailing on site (the so-called “refusal density”). A minimum density is usually specified as a
percentage of the modified AASHTO density, normally between 98 and 102% for bitumen
stabilised bases.
Quality control
Briquettes (for strength testing) are normally manufactured from samples taken immediately
behind the recycler. These briquettes must be made before the emulsion breaks, thereby obtaining
specimens that reflect the compacted material on the road. Often the only way that this can be
achieved is by having a mobile compaction facility on site to manufacture the briquettes.
Alternatively, cores can be extracted at a later date once the layer has fully cured.
Curing
In order to gain strength, an emulsion mix must dispel excess water, or cure. Although some
materials stabilised with bitumen emulsion may achieve their full strength within a short period of
time (one month), curing can take longer than a year with other materials. The length of this
period is affected by field moisture content, emulsion/aggregate interaction, local climate
(temperature, precipitation and humidity) and voids in the mix. Cement addition has a significant
impact on the rate of gain of strength. This is particularly useful where traffic is to be
accommodated on a recycled layer shortly after treatment, Research, however, has shown that
adding more than 2% by mass negatively affects the fatigue properties of the stabilised layer. For
this reason the application rate of cement is usually limited to preferably 1.5% maximum but an
absolute maximum of 2%.


2.9 Foamed Bitumen
In order to mix bitumen with road-building aggregates, you first need to considerably reduce the
viscosity of the cold hard binder. Traditionally, this was done by heating the bitumen and mixing
it with heated aggregates to produce hot mix asphalt. Other methods of reducing the bitumen
viscosity include dissolving the bitumen in solvents and emulsification. Prof. Csanyi came up
with the idea of introducing moisture into a stream of hot bitumen, which effects a spontaneous
foaming of the bitumen (similar to spilling water into hot oil). The potential of foamed bitumen for
use as a binder was first realised in 1956 by Dr. Ladis H. Csanyi, at the Engineering Experiment
Station in Iowa State University. Since then, foamed asphalt technology has been used
successfully in many countries, with corresponding evolution of the original bitumen foaming
process as experience was gained in its use. The original process consisted of injecting steam into
hot bitumen. The steam foaming system was very convenient for asphalt plants where steam was
readily available but it proved to be impractical for in situ foaming operations, because of the need
for special equipment such as steam boilers. In 1968, Mobil Oil Australia, which had acquired the
patent rights for Csanyi’s invention, modified the original process by adding cold water rather than
steam into the hot bitumen. The bitumen foaming process thus became much more practical and
economical for general use.[4]

Figure 2-2 schematic diagram of foamed bitumen production
The foamed bitumen, or expanded bitumen, is produced by a process in which pressurized water
and compressed air is injected into the hot bitumen (155-180 0c), resulting in spontaneous
foaming. The physical properties of the bitumen are temporarily altered when the injected water,


on contact with the hot bitumen, is turned into vapour which is trapped in thousands of tiny
bitumen bubbles. In the foam state the bitumen has a very large surface area and extremely low
viscosity making it ideal for mixing with aggregates however the foam dissipates in less than a
minute and the bitumen resumes its original properties. In order to produce foamed asphalt mix,
the bitumen has to be incorporated into the aggregates while still in its foamed state. A distinct
difference between foamed asphalt mixes and conventional asphalt stabilised mixes is the way in
which the bitumen is dispersed through the aggregate. In the later case the bitumen tends to coat
all particles whilst in the foamed mixes the larger particles are not fully coated. The foamed
bitumen disperses itself among the finer particles forming a mortar which binds the mix together.
Foamed bitumen mixes can achieve stiffness close to those of cement treated bases (3000 MPa)
but remains flexible like asphalt mix.[5]

2.10 Characterization of Foamed Bitumen
Foamed bitumen is characterized by two primary properties:
1. Expansion Ratio that is a measure of the viscosity of the foam and will determine how
well it will disperse in the mix. It is calculated as the ratio of the maximum volume of
foam relative to its original volume or
Foam ratio, it is calculated as the maximum expanded volume of bitumen foam to its
weight and
2. Half-Life is a measure of the stability of the foam and provides an indication of the rate of
collapse of the foam. It is calculated as the time taken in seconds for the foam to collapse
to half of its maximum volume.
The “best” foam is generally considered to be the one that optimizes both expansion and half-life.


Figure 2-3: Bitumen Foam characterization

2.11 Factors influencing foam properties
The expansion ratio and half-life of foamed bitumen is influenced by:
Water addition: Increasing the amount of water injected into the bitumen effectively increases the
volume of foam produced by a 1500 times multiplier. Thus, increasing the amount of water
increases the size of the bubbles created, causing the expansion ratio to increase. However,
increasing the size of the individual bubbles reduces the film thickness of the surrounding
bitumen, making it less stable and resulting in a reduction in half-life. Hence, the expansion ratio
and half-life are inversely related to the amount of water that is added,
Bitumen type: Bitumens with penetration values between 80 and 150 are generally used for
foaming, although harder bitumens that meet the minimum foaming requirements (explained
below) have been successfully used in the past. For practical reasons, harder bitumens are
generally avoided as they produce poorer quality foam, leading to poorer dispersion.


Bitumen source: Some bitumens foam better than others due to their composition. For example,
the foaming properties of bitumens from Venezuela far exceed those from most other sources.
Bitumen temperature: The viscosity of bitumen enjoys an inverse relationship with temperature;
as the temperature increases, its viscosity reduces. Logically, the lower the viscosity, the bigger
the size of bubble that will form when the water changes state in the foaming process. Since this
process draws heat energy from the bitumen, the temperature before foaming needs to exceed 160
ºC to achieve a satisfactory product.
Bitumen and water pressure: Bitumen and water are injected into the expansion chamber through
small diameter openings. Increasing the pressure in the supply lines causes the flow through these
openings to disperse (atomize). The smaller the individual particles, the larger the contact area
available, thereby improving the uniformity of the foam;
Additives: There are numerous proprietary products on the market that will affect the foaming
properties of bitumen, both negatively (anti-foaming agents) and positively (foamants). Foamants
are usually only required where bitumen has been treated with an anti-foaming agent (normally
during refining process). Most foamants are added to the bitumen prior to heating to application
temperatures and tend to be heat-sensitive; implying that their effect is short lived. To reap the
benefits of adding a foamant, the bitumen must therefore be used within a few hours. However,
these products are generally expensive and are usually only considered as a last resort to
improving the foaming properties of stubborn bitumen. (Cutting back the bitumen with diesel oil
has proved successful in reducing the viscosity of the bitumen sufficiently to achieve acceptable
foam. However, this is not recommended unless carried out by the bitumen supplier.)
Acceptable foaming characteristics
The bitumen intended to be used for foaming should be tested in the laboratory to determine the
foaming characteristics. The objective of this exercise is to find that combination of water addition
and bitumen temperature at which the optimal foam (highest Expansion Ratio and Half-Life) is
achieved. As described above, every bitumen is different and even different batches of bitumen
from the same source will vary. However, by following the simple laboratory procedure, the water
application and bitumen temperature is determined for each bitumen and these are then used on
site for full-scale foamed bitumen stabilisation. There are no upper limits to foaming
characteristics and the aim should always be to produce the best quality foam for stabilisation.
Problems are only encountered when a bitumen fails to produce a “good” foam, necessitating that


lower limits be recognized. Normally accepted minimum values for expansion ratio and half-life
for stabilising material at 25 ºC are:
Expansion Ratio 10 times and Half-Life 8 seconds.
Experience has shown that adequate foam dispersion and effective stabilisation is possible
when the expansion ratio is as low as 8 times and the half-life is only 6 seconds. However,
factors other than the foaming characteristics are often responsible, such as elevated material
temperatures. During his research into foamed bitumen during the late 1990s, Prof. Jenkins
developed the concept of a “Foam Index” to measure the combination of expansion ratio and half-
life. He defined this Foam Index as the area under the curve obtained by plotting Expansion Ratio
against Half-life, concluding that the better the foaming properties, the greater the Foam Index and
the better the stabilised product achieved. His research went on to compare the effect of Foam
Index with the temperature of the material at the time of mixing, concluding that as the
temperature of material increases, a lower Foam Index can be used to achieve effective
stabilization.[7]

2.12 Dispersion of foamed bitumen
Unlike hot-mix asphalt, material stabilised with foamed bitumen does not appear black. This
results from the coarser particles of aggregate not being coated with bitumen. When foamed
bitumen comes into contact with aggregate, the bitumen bubbles burst into millions of tiny
bitumen droplets that seek out and adhere to the fine particles, specifically the fraction smaller
than 0.075 mm. The bitumen droplets can exchange heat only with the filler fraction and still have
sufficiently low viscosity to coat the particles. The foamed mix results in a bitumen-bound filler
that acts as a mortar between the coarse particles, as shown previously in Figure 4.1. There is
therefore only a slight darkening in the color of the material after treatment. The addition of
cement, lime or other such fine cementitious material (100 % passing the 0.075 mm sieve) assists
the bitumen to disperse, in particular where the recycled material is deficient in fines.


Figure 2-4: Foamed bitumen dispersion and binding in the treated mix

2.13 Material suitability for foamed bitumen treatment
The foamed bitumen process is suitable for treating a wide range of materials, ranging from sands,
through weathered gravels to crushed stone and RAP. Aggregates of sound and marginal quality,
from both virgin and recycled sources have been successfully utilized in the process in the past. It
is important, however, to establish the boundaries of aggregate acceptability, as well as to identify
the optimal aggregate composition for foamed bitumen mix production. Material that is deficient
in fines will not mix well with foamed bitumen. As depicted in Figure 4.11, the minimum
requirement is 5% passing the 0.075 mm (No. 200) sieve. When a material has insufficient fines,
the foamed bitumen does not disperse properly and tends to form what are known as “stringers”
(bitumen rich agglomerations of fine material) throughout the recycled material. These stringers
vary in size according to the fines deficiency, a large deficiency will result in many large stringers
which will tend to act as a lubricant in the mix and lead to a reduction in strength and stability.


Figure 2-5: Material gradation envelops
Simple laboratory gradation tests carried out on representative samples taken from the existing
road will indicate any potential deficiency in the fines content. This can be rectified by importing a
suitable fine material and spreading on the road surface prior to recycling. Cohesive materials
should, however, be treated with care as standard laboratory gradings will indicate a high
percentage passing the 0.075 mm sieve, whilst in the field the quality of mixing is often poor. This
is due to the cohesive nature of the material causing the fines to bind together, thereby making
them unavailable to disperse the foamed bitumen. Comparison of washed and unwashed grading
tests carried out in the laboratory will indicate the likelihood of this problem developing, the
unwashed grading giving an indication of the available fines. Material that is deficient in fines can
be improved by the addition of cement, lime or other such material with 100 % passing the 0.075
mm sieve. However, the use of cement in excess of 1.5 % by mass should be avoided due to the
negative effect on the flexibility of the stabilised layer. The envelopes provided in Figure 2.5 are
broad and can be refined by targeting a grading that provides the lowest voids in the mineral
aggregate. This produces foamed bitumen mixes with the most desirable mix properties. A unique
relationship for achieving the minimum voids, with an allowance for variation in the filler content,
is shown in equation. This relationship is useful as it provides flexibility with the filler content of a
mixture. A value of n = 0.45 is utilised to achieve the minimum voids.

Where: d = selected sieve size (mm)


P = percentage by mass passing a sieve of size d (mm)
D = maximum aggregate size (mm)
F = percentage filler content (inert and active)
n = variable dependent on aggregate packing characteristics (0.45)
Achieving a continuous grading on the fraction less than 2 mm is important for the proper
dispersion of the foamed bitumen and easier compaction, thereby reducing voids and the
material’s susceptibility to water ingress. Where necessary, therefore, consideration should be
given to blending two materials to improve the critical grading characteristics.

2.14 Recycling with foamed bitumen
Points to be considered while treating with Foamed bitumen
Material temperature
Aggregate temperature is one of the primary factors influencing the successful dispersion of
foamed bitumen and, consequently, the strength achieved in the new pavement layer. As
mentioned above, the Foam Index concept developed by Prof. Jenkins represents the combined
foaming properties of bitumen (expansion ratio and half-life). His research finding showed that the
Foam Index and aggregate temperature (at the time of mixing) were important factors in the
dispersion achieved. Higher Foam Indices (i.e. better expansion and half-life) are necessary for
achieving a satisfactory mix at lower temperatures. Although the implications of these findings are
significant, it is important to compare laboratory conditions to those encountered in the field. The
quality of foam produced by a laboratory unit is always inferior to that produced by a large
recycler, the major reasons being higher working pressures in the field and continuity of operation
allowing the system to function at higher temperatures. There is therefore a shift between
laboratory and field measurements and, for this reason, it is important to check the foaming
properties in the field. These measurements should then be compared with the temperature of the
aggregate (not the road surface) and the results checked with the guidelines in Table. When the
temperature of the aggregate drops below 10 °C, foamed bitumen treatment should not be
considered.


Table2. 12: Foamed bitumen dispersion (ability to mix)

Consistency of bitumen supply
When coupling a new tanker to the recycler, two basic checks should be conducted to ensure that
the bitumen is acceptable for foaming:
– The temperature of the bitumen in the tanker should be checked using a calibrated thermometer
(gauges fitted to tankers are notoriously unreliable); and
– The foaming quality should be checked using the test nozzle on the recycler. This check should
be delayed until at least 100 liters of bitumen has passed through the spraybar whilst recycling in
order to obtain a truly representative sample.
Bitumen flow
Bitumen delivered to site by tankers that are fitted with fire-heated flues is sometimes
contaminated with small pieces of carbon that form on the sides of the flues whilst heating.
Draining the last few tons from the tanker tends to draw these unwanted particles into the
recycler’s system and can cause blockages. This problem is easily resolved by ensuring the
effectiveness of the filter in the delivery line. Any unusual increase in pressure will indicate that
the filter requires cleaning, a procedure that should anyway be undertaken on a regular basis (e.g.
at the end of every shift).
Bitumen pressure
The quality of foam is a function of bitumen operating pressure. The higher the pressure, the more
the stream of bitumen will tend to “atomise” as it passes through the jet into the expansion
chamber. This ensures that small bitumen particles will come in contact with the water that
similarly enters the expansion chamber in an atomised form, thereby promoting uniformity of
foam. If the bitumen were to enter the expansion chamber as a stream (as it does under low
pressures) the water would impact on only one side of the stream, creating foam, but the other side
would remain as unfoamed hot bitumen. It is therefore imperative to maintain a minimum
operating pressure above 3 bars.


Application of active filler
As described above, it is standard practice to add a small amount of cement or other such
cementitious stabilising agent when recycling with foamed bitumen. Care should be taken when
pre-treating with cement since the hydration process commences as soon as the dry powder comes
into contact with moisture, binding the fines and effectively reducing the 0.075 mm fraction. The
quality of the mix when foamed bitumen is subsequently added will be poor due to insufficient
fines being available to disperse the bitumen particles. Cement should therefore always be added
in conjunction with the foamed bitumen.
Table2. 13: Typical foamed bitumen contents relative to key aggregate fractions
Percent passing
Foamed bitumen content, %
4.75 mm 0.075 mm
3–5 3
5 – 7.5 3.5
< 50 (Gravel)
7.5 – 10 4
> 10 4.5
3–5 3.5
5 – 7.5 4
> 50 (Sands)
7.5 – 10 4.5
> 10 5

Table2. 14: Tentative binder and additional treatment requirements
Material type Optimum range of Additional requirements
binder
Well graded clean gravel 2 to 2.5%
Well graded marginally clayey/silty 2 to 4.5%
gravel
Poorly graded marginally clayey gravel 2.5 to 3%
Clayey gravel 4 to 6% Lime modification
Well graded clean sand 4 to 5% Filler
Well graded marginally silty sand 2.5 to 4%
Poorly graded marginally silty sand 3 to 4.5% Low penetration bitumen,


filler
Poorly graded clean sand 2.5 to 5% filler
Silty sand 2.5 to 4.5%
Silty clayey sand 4% Possibly lime
Clayey sand 3 to 4% Lime modification

Moisture Conditions
The moisture content during mixing and compaction is considered by many researchers to be the
most important mix design criteria for foamed asphalt mixes. Moisture is required to soften and
breakdown agglomerations in the aggregates, to aid in bitumen dispersion during mixing and for
field compaction. Insufficient water reduces the workability of the mix and results in inadequate
dispersion of the binder, while too much water lengthens the curing time, reduces the strength and
density of the compacted mix and may reduce the coating of the aggregates. The optimum
moisture content (OMC) varies, depending on the mix property that is being optimized (strength,
density, water absorption, swelling). However, since moisture is critical for mixing and
compaction, these operations should be considered when optimizing the moisture content.
Investigations by Mobil Oil suggest that the optimum moisture content for mixing lies at the “fluff
point” of the aggregate, i.e. the moisture content at which the aggregates have a maximum loose
bulk volume (70 % - 80 % mod AASHTO OMC) . However, the fluff point may be too low to
ensure adequate mixing (foam dispersion) and compaction, especially for finer materials. The
optimum mixing moisture content occurs in the range of 65 - 85 per cent of the modified
AASHTO OMC for the aggregates. The concept of optimum fluid content as used in granular
emulsion mixes may also be relevant to foamed asphalt. This concept considers the lubricating
action of the binder in addition to that of the moisture. Thus the actual moisture content of the mix
for optimum compaction is reduced in proportion to the amount of binder incorporated. The best
compactive moisture condition occurs when the total fluid content (moisture + bitumen) is
approximately equal to the OMC. [4]
Processing time
No specific time limit is placed on working with foamed bitumen. Provided the moisture content
of the material is maintained close to the optimum moisture content, the working period can be
extended.
Curing Conditions


Studies have shown that foamed asphalt mixes do not develop their full strength after compaction
until a large percentage of the mixing moisture is lost. This process is termed curing. Curing is the
process whereby the foamed asphalt gradually gains strength over time accompanied by a
reduction in the moisture content. A laboratory mix design procedure would need to simulate the
field curing process in order to correlate the properties of laboratory- prepared mixes with those of
field mixes. Since the curing of foamed asphalt mixes in the field occurs over several months, it is
impractical to reproduce actual field curing conditions in the laboratory. An accelerated laboratory
curing procedure is required, in which the strength gain characteristics can be correlated with field
behaviour, especially with the early, intermediate and ultimate strengths attained. This
characterization is especially important and required when structural capacity analysis is based on
laboratory-measured strength values. Most of the previous investigations have adopted the
laboratory curing procedure proposed by Bowering (1970), i.e. 3 days oven curing at a temperature
of 60° C. This procedure results in the moisture content stabilizing at about 0 to 4 per cent, which
represents the driest state achievable in the field. In the present study the specimen are cured for 72
hours at 40 0C temperature only.
Density
Generally density increases to a maximum and decreases as the binder content of a foamed asphalt
mix increases. The strength of foamed asphalt mixes depends to a large extent on the density of
the compacted mix. Compaction should always aim to achieve the maximum density possible
under the conditions prevailing on site (the so-called “refusal density”). A minimum density is
usually specified as a percentage of the modified AASHTO density, normally between 98 % and
102 % for foamed bitumen stabilised bases. A density gradient is sometimes permitted by
specifying an “average” density. This means that the density at the top of the layer may be higher
than at the bottom. Where specified, it is normal also to include a maximum deviation of 2% for
the density measured in the lowest one-third thickness of the layer. Hence, if the average density
specified is 100%, then the density at the bottom of the layer must be more then 98 %. For better
quality aggregates (e.g. CBR > 80 %) it is advisable to use an absolute density specification such
as Bulk Relative Density or Apparent Relative Density of the aggregate.
Engineering Properties
The results of previous studies all confirm that strength parameters such as Resilient Modulus,
CBR and stability are optimized at a particular intermediate binder content. The most common
method used in the selection of the design binder content was to optimize the Marshall stability and


minimize the loss in stability under soaked moisture conditions. The major functions of foamed
bitumen treatment are to reduce the moisture susceptibility, to increase fatigue resistance and to
increase the cohesion of the untreated aggregate to acceptable levels. The design foamed bitumen
content could also be selected as the minimum (not necessarily optimum) amount of binder which
would result in a suitable mix.

Moisture Susceptibility
The strength characteristics of foamed asphalt mixes are highly moisture-dependent at low binder
contents. Additives such as lime or Cement reduced the moisture susceptibility of the mixes.
Higher bitumen contents also reduce moisture susceptibility because higher densities are
achievable, leading to lower permeabilities (lower void contents), and to increased coating of the
moisture-sensitive fines with binder. The moisture susceptibility of the material is usually
determined in terms of the Tensile Strength Retained (TSR) by 100 mm briquettes, using below
equation.

Temperature Susceptibility
Foamed asphalt mixes are not as temperature-susceptible as hot-mix asphalt, although both the
tensile strength and modulus of the former decrease with increasing temperature. Bissada (1987)
found that, at temperatures above 30° C, foamed asphalt mixes had higher moduli than equivalent
hot-mix asphalt mixes after 21 days’ curing at ambient temperatures. In foamed asphalt, since the
larger aggregates are not coated with binder, the friction between the aggregates is maintained at
higher temperatures. However the stability and viscosity of the bitumen-fines mortar will decrease
at high temperatures, thus accounting for the loss in strength.

Unconfined Compressive Strength (UCS) and Tensile Strength
Bowering (1970) suggested the following UCS criteria for foamed asphalt mixes used as a base
courses under thin surface treatments (seals): 0.5 MPa (4 day soaked) and 0.7 MPa (3 day cured at
60° C). Bowering and Martin (1976) suggested that in practice the UCS of foamed asphalt
materials usually lie in the range 1.8 MPa to 5.4 MPa and estimated that the tensile strengths of
foamed asphalt materials lay in the range 0.2 MPa to 0.55 MPa, depending on moisture condition.


Bitumen stabilised material is normally evaluated using the Indirect Tensile Strength (ITS) in
preference to Marshall testing with the fallowing advantages.
Simple to conduct the test
Specimen and the equipment are the same as those used for a Marshall testing machine.
The coefficient of variation of the test results is low as compared to other test methods and
This can be used to test under a static load i.e. a single load till failure.
For good performance, cured foamed asphalt samples should have minimum Indirect Tensile
Strengths of 100 kPa when tested in a soaked state and 200 kPa when tested dry.

Stiffness - Resilient Modulus
As with all viscoelastic bituminous materials, the stiffness of foamed asphalt depends on the
loading rate, stress level and temperature. Generally, stiffness has been shown to increase as the
fines content increases. In many cases the resilient moduli of foamed asphalt mixes have been
shown to be superior to those of equivalent hot-mix asphalt mixes at high temperatures (above 30°
C). Foamed asphalt can achieve stiffnesses comparable to those of cement-treated materials, with
the added advantages of flexibility and fatigue resistance.

Abrasion Resistance
Foamed asphalt mixes usually lack resistance to abrasion and ravelling and are not suitable for
wearing/friction course applications.
Fatigue Resistance
Fatigue resistance is an important factor in determining the structural capacity of foamed asphalt
pavement layers. Foamed asphalt mixes have mechanical characteristics that fall between those of
a granular structure and those of a cemented structure. Bissada (1987) considers that the fatigue
characteristics of foamed asphalt will thus be inferior to those of hot-mix asphalt materials. Little et
al (1983) provided evidence of this when he showed that certain foamed asphalt mixes exhibited
fatigue responses inferior to those of conventional hot-mix asphalt or high quality granular
emulsion mixes.


2.15 The benefits of foamed bitumen stabilisation
The following advantages of foamed asphalt are well documented:
• The foamed binder increases the shear strength and reduces the moisture susceptibility of
granular materials. The strength characteristics of foamed asphalt approach those of
cemented materials, but foamed asphalt is flexible and fatigue resistant.
• Foam treatment can be used with a wider range of aggregate types than other cold mix
processes.
• Reduced binder and transportation costs, as foamed asphalt requires less binder and water
than other types of cold mixing.
• Saving in time, because foamed asphalt can be compacted immediately and can carry
traffic almost immediately after compaction is completed.
• Energy conservation, because only the bitumen needs to be heated while the aggregates are
mixed in while cold and damp (no need for drying).
• Environmental side-effects resulting from the evaporation of volatiles from the mix are
avoided since curing does not result in the release of volatiles.
• Foamed asphalt can be stockpiled with no risk of binder runoff or leeching. Since foamed
asphalt remains workable for much extended periods, the usual time constraints for
achieving compaction, shaping and finishing of the layer are avoided.
• Foamed asphalt layers can be constructed even in some adverse weather conditions, such
as in cold weather or light rain, without significantly affecting the workability or the
quality of the finished layer.
The limitations are:
• Requires a suitable grading of fines in the pavement material
• Purpose built equipment and experienced operators are required
• A relative lack of abrasion resistance at surface and requires consideration of a good
surface course over the foamed bitumen treated layer.
Where would we consider this rehabilitation option?
This effective pavement rehabilitation option may be considered in most situations, such as:
• A pavement has been repeatedly patched to the extent that pavement repairs are no longer
cost effective;


• A weak granular base overlies a reasonably strong subgrade.
• A granular base too thin to consider using cementitious binders
• Conventional reseals or thin asphalt overlays can no longer correct flushing problems.
• An alternative to full-depth asphalt in moderate to high trafficked roads.
• Unfavorable wet cyclic conditions unsuitable for granular construction.
• Situations where an overlay is not possible due to site constraints e.g. entries to adjacent
properties & flood prone areas
• A requirement to complete the rehabilitation quickly to prevent disruption to business or
residents


Table2.15: Comparison between different types of bitumen applications
Factor Bitumen Emulsion Foamed Bitumen Hot Mix Asphalt
Aggregate types Crushed rock Crushed rock Crushed rock
applicable Natural gravel Natural gravel 0 to 50% RAP
RAP, Cold mix RAP, stabilised
RAP, stabilised Marginal (Sands)
Bitumen Mixing 20 0C to 70 0C 160 0C to 180 0C 140 0C to 180 0C
Temperature (Before foaming)
Aggregate Ambient (cold) Ambient (cold) Hot only
temperature during (140 0C to 200 0C)
mixing
Moisture content 90% of OMC minus Below OMC Dry
during mixing 50% of emulsion (e.g 65% to 95% of
content OMC)
Type of coating of Partial coating of Coating of fine Coating of all
aggregate coarse particles and particles only with aggregate particles
cohesion of mix with “spot welding” of mix with controlled film
bitumen / fines mortar from the bitumen / thickness
fines mortar
Construction and Ambient Ambient 140 0C to 160 0C
compaction
temperature
Rate of initial strength Slow Medium Fast
gain
Modification of Yes Unsuitable Yes
binder
Important parameters Emulsion type Half life Penetration
of binder Residual bitumen Expansion ratio Softening point
Breaking time Viscosity
Curing


2.16 Case studies

Experience in India:

2.16.1 Emulsion Cold Recycling Rehabilitation Project-Hyderabad
Project location Toli chowki area, Hydrabad
The road connecting Rethibowli and Gachibowli. The traffic made
up of cars, light vans, city buses and large delivery trucks.
Recycling method The rehabilitation method chosen for this road was Cold In Place
Recycling using an Emulsion as the binding agent. The Cold In-
Place Recycling option was chosen for the following reasons:
• Lower cost
• Ability to keep road open to business traffic
• Speed of operation
Road details Width of the road: 14m
Length of the road: 400m
Depth of the recycled layer: 120mm
Material composition RAP: 91%
Fine aggregate (P-2.36mm): 4%
Cement: 2%
Bitumen Emulsion: 3%;

Construction:
• Initially calculated amount of 2% of cement by weight of recycled mix was placed over the
road to be recycled. Later around 2% of fine aggregate passing 2.36mm was uniformly
spread over the section.
• With the help of recycler along with emulsion tanker the recycling job was carried out after
milling to a depth of 120mm of the existing surface while simultaneously mixing the
cement, emulsion (@ 3%), water and milled material to form a homogeneous mixture.
• The recycler is equipped with tamping screed, relayed the recycled material and at the
same time pre-compacted it.


• The laid recycled layer was compacted with a 15tonne vibratory roller. Initially high
amplitude and low frequency mode was selected and later after few passes the mode was
changed to low amplitude and high frequency so as to ensure proper compaction
throughout the recycled thickness.
• Next to rolling with the vibratory roller, a pneumatic tyred roller was used to complete the
final process of compaction.
• After one day water was sprinkled over the laid surface to enable proper curing.
• Later the road was opened to the traffic. However it was felt appropriate to provide a layer
of tack coat followed by a surface course of SDBC.


Figure2.6: A view of recycling process progress in Hyderabad

Figure2.7: Aggregate Spread over the layer to be recycled to correct the Gradation


Figure2.8: Recycling crew in action

Figure2.9: Recycled layer after pre-compaction


Figure2.10: Compacting the recycled layer

Figure2.11: Tack coat application over the recycled and compacted layer


Figure2.12: Finished surface of the recycled layer


2.16.2 Foam bitumen cold recycling rehabilitation project-Bangalore
Existing Pavement Kumbalgodu is an Industrial area, traffic made up of cars, light
vans and large delivery trucks. The road is 5m wide and average
asphalt thickness of 20mm.
Recycling Method In-Plant Cold Recycling
Project location Kumbalgodu industrial area phase-I, Bangalore.
A street road connecting state highway No:17 (Bangalore-Mysore)
and some industries (Pressman India Pvt. Ltd, Karnataka cold
storage Pvt. Ltd. etc.)
Road details Width of the road: 5m
Length of the road: 400m
Depth of the Recycled layer: 100mm
Material sourced from RAP material from BC layer of SH-17 from 31 km to 33 km.
Crusher Stone Dust from BIDADI village quarry located at
35+100 km of SH-17.
Bitumen used for foaming is of 80/100 penetration grade.
Material composition RAP: 75% by wt of aggregate;
Stone Dust: 25% by wt of aggregate
Cement: 1.5% by wt of aggregate;
Foamed bitumen: 3.5% by wt of mix;
Water: 3% by wt of mix

Construction:
• The road to be paved with plant recycled material was cleaned and sprinkled with water to
damp the surface to ensure proper bond.
• Foamed bituminous recycled mix was prepared in the mobile mixing plant (KMA-200)
using RAP, Stone dust, Cement and Foamed bitumen in formulated proportions just near
by the working site.
• Recycled plant mix was transported by dumper and is dumped in to the hopper of the paver
to lay the foamix.


• The compaction process was started with vibratory roller and is finished with pneumatic
tyred roller to achieve specified density and smooth finished surface.
• The recycled road surface was opened to the traffic after 12 hours of construction.
• Two coats of tack coat application and dust spreading was being carried out to seal the
surface in a gap of 4 days.


Figure2.13: Loader used to load the materials in to the mobile plant

Figure2.14: Cement and hot bitumen supplied to the plant


Figure2.15: Recycled material being discharged in to the dumper

Figure2.16: Recycled foamix being dumped in to the paver hopper


Figure2.17: Initial compaction with vibratory roller

Figure2.18: Final compaction with pneumatic tyred roller


Experience in abroad:

2.16.3 Emulsion Cold Recycling Rehabilitation Project. Citizen Court, Toronto,
June 2003
Existing Pavement Citizen Court is an Industrial area, traffic made up of cars, light
vans and large delivery trucks (Container type). The road is
10.4m wide with and average asphalt thickness of 90mm. The
existing pavement is 18 years old and has reached the end of it’s
useful life, distress is mainly localised base failure with alligator
cracking.
Rehabilitation Method: The rehabilitation method chosen for Citizen Court was Cold In
Place Recycling using an Emulsion as the binding agent. The
Cold In-Place Recycling option was chosen for the following
reasons:
• Lower cost
• Ability to keep road open to business traffic
• Speed of operation
Design Mix: Depth of cutting 80 mm
Grindings 98.40%
Emulsion 1.60%
Water Added 2.90% and
Finish Course 40 mm Asphalt concrete
Recycling Train The Recycling train consisted: Wirtgen 2200CR (fitted 2.5m
width milling drum), Emulsion Supply tanker. The Emulsion
Tanker is pushed by the Wirtgen 2200CR, the recycler therefore
controls the speed of operation, and the emulsion application rate
is proportional to recycler forward speed (Average speed 7.5m /
min.). The water for compaction is drawn from the 2200CR
onboard water tank, 5000 litre capacity. The Compaction
achieved using: Single steel drum vibratory compactor, followed
by Pneumatic Multi Tyred Compactor.


Recycling Sequence of Operation
Pass No 1:
2.5m wide, from centre line out. The total width of the pavement was 10.4m wide, 5.2m half
width. Maximum recycled width with 2 passes of the 2200CR (fitted with 2.5m cutter) was 4.9m,
allowing overlap of 0.1 m at the joint. Therefore, it was necessary to mill 0.5m width x 80mm
depth from kerb outwards, the milled material being windrowed to the side.
Pass No. 2:
The pre-milled material is incorporated into the 2200CR mixing drum, to be treated with
emulsion. Total recycled width after 2 passes 5.2m
Screed set up:
Pass No 1: The screed was set for 2.5m width to match the recycled width.
Pass No 2: The right hand section of the screed is set to 1.55m width, to match half the 2200CR
cutter width plus the pre milled section. The left hand screed width is set to 1.25m width, to match
half the 2200CR cutter width. Right hand screed section set to pave up to kerb edge. Total screed
width in Pass No. 2 is 2.8m.
Total 4 passes required for a 10.4m road width.


Figure2.19: Recycling option used

Figure 2-20: Emulsion tanker and recycler


Figure 2-21: Pre-compacted surface after 1st pass

Figure 2-22: Cold milling from kerb outwards


Figure 2-23: Pre-compacted surface after 2nd pass


2.16.4 Saudi Arabia – A desert road for heavy traffic

The dual-lane Shaybah Access Road, with a total length of more than 380 km, leads from the
Batha main route to the Saudi Aramco Shaybah area in the Rub Al Khali desert. The construction
of a reliable traffic route was imperative for the development of an oil field with affiliated
refinery, and for the heavy-duty traffic to be expected in connection with the transport of
components for the processing plant weighing up to 200 t. Originally built from Marl as an
unbound gravel road only, the total length of the Shaybah Access Road was therefore recycled
within 180 days only using the foamed bitumen technology. During the main construction phase,
three Wirtgen Cold Recyclers WR 2500 and Mobile Slurry Mixing Plants WM 400 were in
operation on site. With the addition of 5% foamed bitumen and 2% cement slurry, a daily average
of approximately 35,000 m2 of existing pavement could be scarified and recycled with the binding
agents down to a depth of 20 cm. In order to optimise the workability and compaction properties
of the existing sub-base, which consisted of Marl and sand, approximately 4% water were added.
In addition to the Wirtgen machines WR 2500 and WM 400, motor graders as well as vibrating
rollers and pneumatic tired rollers were employed to profile and compact the treated material. In
order to ensure an optimum work pattern and to achieve the highest possible quality, two recycling
trains worked staggered behind one another, thus ensuring good adhesion between the individual
machine passes and an optimum profiling of the complete lane. This also enabled the heavy-duty
traffic to pass the ever moving job site during the whole duration of the rehabilitation project.
Finally, a bituminous surface treatment, in the form of a slurry seal, was applied on the recycled
base layer. In an inspection report, road construction experts praised the good suitability of foamed
bitumen as a stabilising agent even under these extreme climatic conditions, as well as its high
economic efficiency. The original plans involving conventional construction methods with
imported crushed aggregate and hot mix asphalt had been rejected as these would have met neither
the economical nor the time frame of this project. Figure 2-24 shows one of the three Wirtgen
recycling trains consisting of a WR 2500 and a Slurry Mixer WM 400 during the economical
rehabilitation of the Shaybah Access Road, In operation 24 hours a day despite extreme climatic
conditions.


Figure 2-24: Recycling of Shaybah Access road


2.16.5 In-Plant recycling using milled asphalt bound with foamed bitumen
Responsible parties
Client: Durban Municipality, Roads Department - City Engineers Unit
Contractor: Milling Techniks
Design Engineers: Siyenza Engineers / Loudon International
Equipment suppliers: Wirtgen South Africa with Wirtgen GmbH (Germany)
Introduction
The Newlands West Drive, which serves as a mayor bus route and arterial to a large residential
area, showed signs of distress in the form of cracking of the existing asphalt layers. The
rehabilitation design called for an overlay on to the existing road of 125 mm thick foamed bitumen
stabilised RAP and 40 mm asphalt surfacing. The alternative conventional rehabilitation method
with the same structural capacity would have been to overlay the existing road with an 100 mm
asphalt binder layer and a 40 mm asphalt surfacing. Due to the increasing volume of stockpiled
RAP at the municipal depots and the relatively low stabilising agent contents required, the
alternative using the in-plant recycling method showed a significant saving for the client. This
project coincided with the 22nd PIARC World Road Congress. Thanks to the future orientated
thinking of the Durban Municipality, an agreement was reached together with Milling Techniks
and Wirtgen South Africa to showcase the in-plant recycling and foamed bitumen technology to
the international road construction industry attending the congress during the week of 20 . 24
October 2003.


Project details Length of road: 1000 m, Width of road: 8 m
Aggregate: Reclaimed Asphalt Pavement (RAP) collected from
various milling contracts and stockpiled at the Durban City council’s
depot.
Stabilising agents: 2 % Foamed bitumen (80/100 penetration grade)
and 1 % cement (OPC)

Equipment utilized RAP sizing plant: Hartl PC 1270 I (Impact crusher)
Mixing Plant: Wirtgen KMA 200
Paving unit: Vögele Super 1800
Compactors: HAMM HD O70V double smooth drum with one
Vibratory and one Oscillation drum; and HAMM GRW 18
(pneumatic tyred roller)
Technical information Design Life: 20 years
Structural capacity: 4,8 million ESALs (80 kN = 8 ton)
Mix properties: Indirect Tensile Strength (150 dia. briquette) > 150
KPa
Retained strength > 90 %
Unconfined Compressive Strength > 1500 KPa
Compaction: > 100 % of modified AASHTO density (1984 kg/m³)


Lab and field eveluation of recycled cold mix

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