Copyright is owned by the Author of the thesis.  Permission is given for 
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FORMULATION DEVELOPMENT AND 

MICROSTRUCTURE ANALYSIS OF A POLYMER 

MODIFIED BITUMEN EMULSION ROAD 

SURFACING 

A Thesis presented 
in partial fulfilment of 

the requirements for the Degree of 
Master of Technology in Product Development 

at Massey University, Palmerston North, New Zealand. 

ALLAN R FORBES 

2000 



11 

ABSTRACT 

The purpose of this research was to develop a formulation for a polymer modified 

bitumen emulsion road surfacing product called microsurfacing to a mid-scale prototype 

stage. A supplementary part of the development was to investigate the polymer-bitumen 

interactions and how they affected the products end properties using confocal 

microscopy. 

The formulation development consisted of three stages: technical design specifications, 

initial design, detailed design. The technical specification was developed to define the 

product performance in quantitative measures, and set the initial formulation parameters 

to work within. The initial design development screened three polymers, four methods of 

adding polymer to the emulsion and two grades of bitumen. Experimental design 

techniques were used to determine the best polymer-bitumen combination and emulsion 

process method. Further experimental investigations consisted of screening three 

emulsifiers and assessing the effect of aggregate cleanliness on the surfacing abrasion and 

curing rate. 

The detailed design used experimental factorial design to examine the effects of polymer 

concentration, emulsifier level, and emulsifier pff oh the emulsion stability, 

microsurfacing wear resistance and cure rate. 

The emulsion residue was observed using confocal microscopy with fluorescence light 

and the microsurfacing mixture using both fluorescent and reflected light. 

The research showed that a emulsion using 100 penetration grade Safaniya bitumen with 

SBR latex polymer post added could provide microsurfacing abrasion resistance of less 

than 100 g/m2
; an improvement of 85% on the minimum specification. The vertical 

permanent deformation was less than the 10% and could not be attained without polymer 

addition. The use of aggregate with a high cleanliness and an alkyl amidoamine 

emulsifier resulted in surfacing cohesion development of 20 kg-cm within 90 minutes, 

which compares closely to the international specification. 



lll 

Unexpected results not reported before were that the emulsion residue from biphase 

modified emulsions had a softening point up to 10°C higher than polymer modified hot 

bitumen with the same polymer concentration. The biphase emulsified binder residue 

also has a very different microstructure to hot modified bitumen and this structure has 

been proposed to help account for the improved resistance to high temperature and 

applied stress. 

Modifications to the formulation are to improve the emulsion settlement and should focus 

on the density difference between the bitumen and polymer latex. 

This research has shown that a microsurfacing roading product can be successfully 

formulated with New Zealand bitumen and aggregate sources to meet key specified 

performance requirements. By systematically investigating the effects of materials on the 

performance properties of the product, a formulation ready for a mid-scale experiment 

has been proposed. 



IV 

ACKNOWLEDGEMENTS 

Dr Richard Haverkamp for being the chief supervisor for this project, for his willingness 

to assist, guide, critique and encourage throughout the work. 

Tom Robertson for also supervising this project, for his advice, feedback, and ability to 

give valued points of view that I had not thought of 

A huge thanks to Higgins Development Technologist Sean Bearsley for his considerable 

time and effort in helping with technical advice and laboratory development, without 

which the progress gained would not have been possible. 

Higgins Group Technical Manager John Bryant for initiating this research, and his valued 

advice and feedback 

Dr Tony Paterson and Associate Professor Bob Chong for their valued inputs into the 

laboratory development work. 

Liz Nickless for training and assistance with the confocal microscopy technique. 

The research work was financially supported by the Graduate Research in Industry 

Fellowship and the Higgins Group; the research opportunity and assistance has been 

appreciated. 

To my family for their support over the years I have been studying. 

Finally, to Megan for her support and understanding over the last 12 months. 



ABSTRACT 

ACKNOWLEDGEMENTS 

TABLE OF CONTENTS 

LIST OF TABLES 

LIST OF FIGURES 

LIST OF APPENDICES 

GLOSSARY 

CHAPTERS 

1. INTRODUCTION 

1.1 Background 

TABLE OF CONTENTS 

1.2 Microsurfacing Product Design 

1.3 Technical Specifications 

1.4 Initial Laboratory Development· 

1.5 Formulation Detailed Design 

1.6 Confocal Microscopy Research 

1.7 Research Aims and Objectives 

1.7.1 Aim 

1.7.2 Research Objectives 

1.7.3 Constraints 

2. REVIEW OF BITUMEN EMULSION SCIENCE, POLYMER 

MODIFICATION, AND MICROSURFACING TECHNOLOGY 

2.1 Introduction 

2.2 Bitumen Emulsification 

2.3 Advantages of Bitumen Emulsions 

2.4 Emulsion Classification 

2.5 Raw Materials 

2.5.1 Bitumen 

2.5.2 Emulsifiers 

2.5.3 Water 

V 

11 

lV 

V 

XI 

Xlll 

xv 

. XVI 

1 

1 

2 

2 

3 

3 

4 

5 

5 

5 

5 

6 

9 

9 

10 

11 

12 

12 

17 

19 



Vl 

2.5.4 Acids 19 

2.5.5 Additives 19 

2.6 Emulsion Production 20 

2.6.1 Stirring 21 

2.6.2 Homogenizers 21 

2.6.3 Colloid Mills 22 

2.6.4 Processing Variables 22 

2.7 Emulsion Formulation Characteristics 23 

2.7.1 Emulsion Stability 24 

2.7.2 Breaking Process 25 

2.7.3 Emulsion Adhesion 26 

2.7.4 Cohesion 26 

2.7.5 Viscosity 26 

2.8 Characteristics of General Emulsion Stability 27 

2.8.1 Low Interfacial Tension 28 

2.8.2 Zeta Potential 28 

2.8.3 Electrical Double Layer Repulsions 28 

2.8.4 Narrow Droplet Size Distribution 28 

2.8.5 High Viscosity 28 

2.9 Modification of Bitumen Emulsion Properties 28 

2.9.1 Increasing the Viscosity of the Emulsion 29 

2.9.2 Decreasing the Viscosity of the Emulsion 29 

2.9.3 Changing the Emulsion Breaking Rate 30 

2.9.4 Storage Stability 30 

2.10 Polymer Modified Bitumen and Emulsions 32 

2.10.1 Polymer Modified Bitumen 32 

2.11 Types of Polymer Used 33 

2.11.1 Plastomers 33 

2.11.2 Elastomers 33 

2.12 Interactions during Manufacture 34 

2.12.1 Grade of Polymer 35 

2.12.2 Physical Form of Polymer 35 



Vil 

2.12.3 Nature and Grade of Bitumen 35 

2.12.4 Mixing Equipment 35 

2.13 Elastomeric Polymers 36 

2.13.1 Styrene Butadiene Styrene (SBS) 36 

2.13.2 Styrene Butadiene Rubber (SBR) 38 

2.13.3 Neoprene (Polychloroprene) 39 

2.13.4 Natural Rubber (Polyisoprene) 39 

2.14 Plastomeric Polymers 40 

2.14.1 Ethylene Methyl Acrylate (EMA) 40 

2.14.2 Ethylene Vinyl Acetate (EV A) 41 

2.15 Bitumen/Polymer Compatibility 42 

2.16 Microscopic Investigations of Bitumen/Polymer Blends 44 

2.17 Polymer Modified Emulsions 45 

2.18 Modified Emulsion Definitions 46 

2.19 Manufacturing Processes 46 

2.20 Polymer Modified Emulsion Properties 48 

2.20.1 Storage Stability 48 

2.20.2 Breaking Process 49 

2.20.3 Choice of Bitumen 49 

2.21 Microsurfacing Technology 50 

2.22 Introduction 50 

2.23 History and Relevance ofMicrosurfacing to New Zealand 50 

2.24 Manufacture of Micro surfacing 51 

2.25 Materials 52 

2.25.1 Polymer Modified Emulsion 53 

2.25.2 Aggregate 53 

2.25 .3 Mineral Filler 54 

2.25.4 Water 54 

2.25.5 Additives 55 

2.26 Mix Design 55 

2.27 Rate of Application 56 

2.28 Weather Limitations 56 



Vlll 

2.29 Chapter Conclusions 56 

3. PRODUCT TECHNICAL SPECIFICATIONS AND REQUIREMENTS 58 

3 .1 Introduction 59 

3.2 Suitability and Addition Levels of Polymers for Emulsification 

3.3 Product Attributes 

3.4 Preliminary Technical Specification for Microsurfacing 

3.4.1 Scope 

3.4.2 Description 

3.4.3 Materials 

3.4.4 Manufacturing Requirements 

3.4.5 Mix Design 

3.4.6 Test Requirements 

4. MATERIALS AND METHODS 

4 .1 Materials 

4.2 Processing Variables 

4.2.1 Colloid Mill 

4.2.2 Bitumen Phase Temperature 

4.2.3 Soap Phase Temperature 

4.2.4 Flow Rates 

4.3 Preparation ofMonophase Modified Emulsions 

4.4 Preparation ofBiphase Modified Emulsions 

4.5 Test Methods 

4.5.1 Emulsion pH 

4.5.2 Viscosity 

4.5.3 Binder Residue 

4.5.4 Emulsion Settlement 

4.5.5 Sieve Residue 

4.5.6 Softening Point 

4.5.7 Laser Scanning Confocal Microscopy (CLSM) 

4.5.8 Wet Track Abrasion 

4.5.9 Loaded Wheel Test 

59 

60 

61 

61 

61 

61 

64 

65 

66 

67 

68 

70 

70 

71 

71 

71 

71 

72 

72 

73 

73 

73 

74 

74 

74 

74 

75 

75 



lX 

4.5.10 Microsurfacing Cohesion 75 

4.5.11 Mix Time 76 

4.6 Process Capability and Test Repeatability 76 

4.7 Development Methodology 78 

4.7.1 Initial Design 78 

4.7.2 Emulsifier Investigation 81 

4.7.3 Aggregate Assessment 82 

4.7.4 Formulation Detailed Design 83 

5. LABO RA TORY DEVELOPMENT RES UL TS 86 

5.1 Introduction 87 

5.2 Initial Design Investigation 87 

5.2.1 SBR Latex Modified Biphase Emulsion Results 87 

5.2.2 Monophase Polymer Modified Emulsion Results 95 

5.2.3 Conclusions 102 

5.3 Emulsifier Investigation Results 104 

5.3.1 Emulsion Viscosity 104 

5.3.2 Emulsion Settlement 105 

5.3.3 Emulsion Sieve Residue 105 

5.3.4 Binder Properties 105 

5.3.5 Microsurfacing Abrasion Resistance 106 

5.3.6 Microsurfacing Cohesion 106 

5.3.7 Mix Time 107 

5.4 Aggregate Investigation Results 107 

5.4.1 Microsurfacing Abrasion Resistance 108 

5.4.2 Microsurfacing Cohesion 108 

5.4.3 Conclusions 109 

5.5 Detailed Design Investigation Results 110 

5.5.1 Final Emulsion pH and Binder Residue 110 

5.5.2 Emulsion Viscosity 113 

5.5.3 Emulsion Settlement 114 

5.5.4 Emulsion Sieve Residue 115 

5.5.5 Binder Softening Point 115 



5.5.6 Microsurfacing Abrasion Resistance 

. 5.5.7 Microsurfacing Permanent Deformation 

5.5.8 Microsurfacing Cohesion 

5.5.9 Microsurfacing Mix Time 

5.6 Determining an Optimum Formulation Range 

6. CONFOCAL MICROSCOPY INVESTIGATIONS 

6.1 Introduction 

6.2 Unmodified Bitumen 

6.3 Hot Polymer Modified Bitumen and Resulting Emulsion Binders 

6.3.1 SBS Modified Binder 

6.3.2 SBR Modified Binder 

6.3.3 EMA Modified Binder 

6.4 Observations ofBiphase Emulsions Containing SBR Latex 

6.4. l Resistance ofMicrostructure to Higher Temperature 

6.4.2 Binder Resistance to Applied Stress 

6.5 Observations of Micro surfacing 

7. DISCUSSIONS AND CONCLUSIONS 

7 .1 Introduction 

7 .2 Initial Product Specification 

7.3 Initial Design 

7.3.1 SBR Latex Biphase Emulsion Investigation 

7.3.2 Monophase Polymer Modified Emulsion Investigation 

7.3.3 Emulsifier Investigation 

7.3.4 Aggregate Investigation 

7.4 Detailed Design Investigation 

7 .5 Confocal Microscopy 

7.6 Recommendations and Further Work 

7.7 Conclusions 

BIBLIOGRAPHY 

APPENDICES 

X 

117 

119 

119 

122 

128 

131 

132 

132 

133 

133 

134 

136 

137 

139 

140 

141 

144 

145 

145 

146 

146 

148 

150 

152 

153 

156 

157 

159 

160 

169 



Xl 

LIST OF TABLES 

Tables 

Table 2-1 Comparison of Viscosity for Polymer Modified Bitumen 47 

Table 2-2 Aggregate Gradings for Microsurfacing 54 

Table 2-3 Microsurfacing Mix Design Guidelines 56 

Table 3-1 Polymer Addition Methods and Concentrations Suitable 60 

Table 3-2 Product Attributes and Material Solutions for Microsurfacing 60 

Table 3-3 Possible Polymers for Microsurfacing 62 

Table 3-4 Possible Quick Setting Emulsifiers 62 

Table 3-5 Grading of Type II Aggregate 63 

Table 3-6 Grading of Type III Aggregate 63 

Table 3-7 Potential Production Characteristics 65 

Table 3-8 Approximate Mix Design Components 65 

Table 3-9 Acceptance Criteria for Microsurfacing Emulsion and Binder 66 

Table 3-10 Acceptance Criteria for Microsurfacing Slurry 66 

Table 4-1 Microsurfacing Emulsifiers 69 

Table 4-2 Grading of Aggregate used for Investigation 70 

Table 4-3 Variation in Laboratory Production Process andTesting Methods 77 

Table 4-4 Initial Emulsion Formulation 79 

Table 4-5 Initial Microsurfacing Mixture Design 79 

Table 4-6 Experimental Design Matrix for SBR Latex Biphase Emulsions 80 

Table 4-7 Initial Design Runs for Producing Mono phase Polymer Modified 

Emulsions 80 

Table 4-8 Formulations for Monophase Polymer Modified Emulsions using 

130/150 Bitumen 81 

Table 4-9 Formulations for Emulsifier Experiment 82 

Table 4-10 Experimental Plan for Aggregate Assessment 82 

Table 4-11 Factors and Levels for Experimental Detailed Design 83 

Table 4-12 Full Factorial Experimental Design Matrix for Three Factors at 

Two Levels 84 

Table 4-13 Experimental Design Treatment Combinations for Three Factors 

and Two Levels 84 



Xll 

Table 4-14 Emulsion Formulation and Processing Conditions for Detailed 

Design 85 

Table 4-15 Microsurfacing Mixture Design for Detailed Design Formulation 85 

Table 5-1 Summary of Test Results from SBR Latex Biphase Emulsion 

Investigation 89 

Table 5-2 Significance of Variables from SBR Latex Biphase Emulsion 

Investigation 90 

Table 5-3 Summary of Test Results from Mono phase Emulsion Investigation 98 

Table 5-4 Slurry Mix Design Results for Monophase Emulsion Investigation 102 

Table 5-5 Summary of Test Results from Emulsifier Investigation 104 

Table 5-6 Test Results from Aggregate Investigation 107 

Table 5-7 Summary of Test Results for Emulsion Detailed Design 111 

Table 5-8 Significance and Effects of Variables Controlling the Emulsion 

and Microsurfacing Properties 112 

Table 5-9 Summary of Significant Effects Controlling the Microsurfacing 

Properties 128 

Table 5-10 Refined Emulsion Formulation for Mid-Scale Trial 130 

Table 5-11 Microsurfacing Mixture Design for Mid-Scale Trial 130 



Xlll 

LIST OF FIGURES 

Figure 

Figure 1-1 Product Design Stages to Develop the Microsurfacing 

Formulation 2 

Figure 2-1 Emulsifier Behaviour on a Bitumen Particle 10 

Figure 2-2 Main Chemical Constituents of Bitumen 13 

Figure 2-3 Cationic Emulsifier 18 

Figure 2-4 Schematic Diagram of an Emulsion Production Process 20 

Figure 2-5 Manufacturing Process ofMonophase Modified Bitumen 

Emulsion 46 

Figure 2-6 Manufacturing Process of a Biphase Modified Bitumen 

Emulsion 48 

Figure 2-7 The Microsurfacing Process 52 

Figure 5-1 Five Day Emulsion Settlement for SBR Biphase Emulsions 92 

Figure 5-2 Slurry Permanent Deformation for SBR Biphase Emulsion 

Investigation 94 

Figure 5-3 Main Effects Plot for Emulsion Viscosity 113 

Figure 5-4 Main Effects Plot for Emulsion Settlement 114 

Figure 5-5 Main Effects Plot for Emulsion Sieve Residue 116 

Figure 5-6 Softening Point Comparison between SBR Polymer Modified 

Emulsion Binder and Hot SBR Polymer Modified Bitumen 116 

Figure 5-7 Main Effects Plot for Abrasion Resistance 118 

Figure 5-8 Changes in Microsurfacing Permanent Deformation by Increased 

Polymer Addition 119 

Figure 5-9 Main Effects Plot for Microsurfacing Cohesion after 60 minutes 120 

Figure 5-10 Regression Plot for Microsurfacing Cohesion after 60 minutes 121 

Figure 5-11 Regression Plot for Microsurfacing Cohesion after 90 minutes 122 

Figure 5-12 Main Effects Plot for Microsurfacing Mix Time 123 

Figure 5-13 Interaction Plot for Mix Time of Polymer and Emulsifier 124 

Figure 5-14 Interaction Plot for Mix Time of Emulsifier and Soap pH 124 

Figure 5-15 Contour Plot for Mix Time of Polymer and Emulsifier Level 126 

Figure 5-16 Contour Plot for Mix Time of Emulsifier and pH Level 127 



}UV 

Figure 6-1 CLSM Fluorescence Image ofUnmodified Bitumen (lO00x 

Magnification) 132 

Figure 6-2 CLSM Fluorescence Image of Unmodified Bitumen Emulsion 

Residue (IO00x Magnification) 133 

Figure 6-3 CLSM Fluorescence Image of Bitumen Modified with 3% SBS 

Polymer ( 400x Magnification) 134 

Figure 6-4 CLSM Fluorescence Images of3% SBR Latex Pre-blended into 

Hot Bitumen a). The Pre-blended SBR-Bitumen Residue after 

Emulsifying b ). ( 1 000x Magnification) 135 

Figure 6-5 CLSM Fluorescence Images of3% EMA Modified Bitumen a). 

EMA-Bitumen Binder Residue after Emulsifying b). (l000x 

Magnification) 136 

Figure 6-6 CLSM Fluorescence Images of 3% SBR Latex Modified Biphase 

Emulsion Binders ( 1 0OOx Magnification) 138 

Figure 6-7 CLSM Fluorescence Image of Biphase Emulsion Residue after 

Heating at 109°C ( 1 000x Magnification) 139 

Figure 6-8 CLSM Fluorescence Image of Biphase Emulsion Binder under 

Shear Strain ( 1 O00x Magnification) 140 

Figure 6-9 CLSM Depth Scan Image ofMicrosurfacing under Fluorescent 

Light ( 1 00x Magnification) 141 

Figure 6-10 CLSM Depth Scan Image ofMicrosurfacing under Reflected 

Light (1 00x Magnification) 142 

Figure 6-11 CLSM Composite Depth Scan Image ofMicrosurfacing with 

Combined Fluorescence/Reflected Light ( 1 00x Magnification) 142 



xv 

LIST OF APPENDICES 

Appendix 

2-1 Comparison of Chemical Fractions within Bitumen Sources 169 

5-1 Emulsion and Microsurfacing Results from SBR Latex Addition Method 

Investigation 170 

5-2 Microsurfacing Mix Design Results for SBR Latex Biphase Emulsion 

Investigation 171 

5-3 Emulsion and Microsurfacing Properties from Monophase Modified 

Emulsion Investigation 172 

5-4 Emulsion and Microsurfacing Properties from Detailed Design 

Investigation 173 

5-5 Contour Plot of Abrasion Loss from Detailed Design for Emulsifier and 

Soap pH Level 174 

5-6 Contour Plot of Abrasion Loss from Detailed Design for Polymer and 

Soap pH Level 175 

5-7 Experimental Error Results from Detailed Design Experiment 176 



Aggregate 

Binder 

Biphase Emulsion 

Break 

Copolymer 

Curing 

Cut-back 

Emulsifier 

Elastomer 

Latex 

Microsurfacing 

XVI 

GLOSSARY 

A hard inert mineral material, such as gravel, crushed rock, or 

sand. 

Material which secures aggregate to road surface. Can comprise 

of bitumen, polymers, solvent or other solid material. 

Polymer modified bitumen emulsion characterised by a dispersed 

phase made up of two types of droplets: bitumen and polymer. 

The destabilisation of an emulsion resulting in the separation of 

emulsified phases ( demulsification). 

A polymeric structure that is composed of at least two different 

monomers in alternating sections or a coupling group of low 

molecular weight. 

The development of mechanical properties of the bitumen binder. 

This occurs after the emulsion has broken and the emulsion 

particles coalesce and bond to the aggregate. 

Bitumen liquefied by blending with petroleum solvents. 

The chemical added to the water and bitumen that keeps the 

bitumen in stable suspension in the water. 

Polymers that can easily undergo large elongation at relatively 

low stress levels and rapidly return to approximately its original 

SIZe. 

An aqueous, stable, colloidal emulsion of a polymer substance. 

A mixture of polymer modified bitumen emulsion, crushed 

graded aggregate, mineral filler, additives, and water. 

Microsurfacing provides thin resurfacing of 10 to 20 mm to the 

pavement and returns traffic use in 1 to 1.5 hours under average 

conditions. 

Monophase Emulsion Polymer modified bitumen emulsion characterised by a dispersed 

phase composed of only polymer modified bitumen droplets. 

Residue 

Wetting 

The bitumen binder that remains after the emulsion has broken 

and cured. 

The reduction of interfacial tension. 



1 

1. INTRODUCTION 

1.1 Backg"round 

The use of polymer modified bitumen emulsions for road sealing maintenance has the 

potential to be an important product area for New Zealand contractors. Unmodified 

bitumen softens under increased temperatures and this results in the pavement deforming 

(Whiteoak, 1990; Transit, 1993; Asphalt Institute, 1994). Common problems encountered 

are loss of stone chips and formation of wheel tracking ruts that cause an uneven surface. 

The loss of stone chips reduces tire traction. Wheel ruts in roads can cause vehicles to 

aquaplane due to water build-up and reduce braking effectiveness. These problems can be 

reduced by the addition of polymer modifiers to the bitumen to increase its strength and 

elasticity (Whiteoak, 1990; Transit, 1993; Bahia et al., 1998; Swanston & Remtulla, 

1998). 

But the only product alternatives in New Zealand to solve these problems are polymer 

modified hot-mix asphalt, or polymer modified hot cut-back* bitumen as a sprayed layer 

covered with graded aggregate (Transit, 1993). Asphalt is expensive and must be laid in 

thick layers. Cutback bitumen contains petroleum solvent to reduce the temperature 

needed to lower the viscosity to a sprayable level. But, the spraying temperature is still 

around 160°C. Another drawback of solvent is that it also reduces the softening point of 

the bitumen, making it more susceptible to heat. The combination of high temperature 

and solvent present a safety risk for workers, high energy costs and environmental 

concerns over solvent evaporation ( Asphalt Institute, 1994; Reed, 1996). Both of these 

options also require the whole section ofroad to be resurfaced even though in many cases 

it is only the wheel ruts that may be the problem. 

In particular the microsurfacing product, which uses a polymer modified bitumen 

emulsion mixed with aggregate, has important benefits. The advantage of bitumen 

emulsions is that they are applied at ambient temperature, and generally require no 

solvent. In the USA and several countries in Europe the microsurfacing product 1s 

common and rapidly gaining acceptance (Asphalt Institute, 1994; Holleran, 1997). 

• Italicised words appear in the glossary. 



2 

Microsurfacing imparts protection to the underlying pavement and provides renewed 

surface friction. Wheel ruts of up to 40 millimetres can be easily filled using this product. 

Microsurfacing is quick setting, which allows traffic rapidly on the pavement. It can also 

be applied in the early evening or even at night-time. 

1.2 Microsurfacing Product Design 

The basic formulation aspects of a microsurfacing consists of: 

1. Polymer modified bitumen emulsion 

2. Graded aggregate 

3. Setting additives 

4. Extra water to wet the aggregate 

The most challenging part of designing a microsurfacing is the emulsion formulation 

(Asphalt Institute, 1994; Holleran, 1997). The experimental work undertaken in this 

research focuses mainly on this part of the product. But, it is important to recognise the 

whole microsurfacing system and the experimental work also includes the emulsion­

aggregate interactions in detail. The formulation development followed a common 

product design approach. The product design approach used in this experimental research 

consisted of the phases shown in Figure 1-1. 

Figure 1-1. Product Design Stages to Develop the Microsurfacing Formulation 

Technical design specifications 

Initial design - material screening 
:~ 

....................... .......... ~.~.~~~.~:.~ .. ~~.~~gn .............................................. 1 ~ 
Scale-up and validation 

Optimal design 

Production and launch 

1.3 Technical Specifications 

Phases covered in 

this research 

Developing a set of technical specifications helps to define the product performance in 

quantitative measures, set the initial formulation parameters to work within and the 

process method to use. A set of preliminary specifications for the product was prepared to 



3 

help guide the initial formulation development. This included suitable materials, process 

method and processing parameters. Performance criteria to compare the experimental 

products against were selected from technical literature. The technical specification 

developed is discussed in chapter 3. 

1.4 Initial Laboratory Development 

The scope of the product materials and their effect on the performance properties requires 

a screening process to adequately assess them. The polymer type and its method of 

addition to the emulsion can add different performance properties to the bitumen binder. 

The polymer can be added to an emulsion in four possible ways and it needed to be 

determined if there were significant performance differences. Bitumen can be supplied in 

different grades and this directly affects the durability of the microsurfacing and also the 

polymer processing method. The emulsifier type can affect the cure rate of the 

microsurfacing, which determines the time frame for allowing traffic on the surfacing. 

Aggregate type and quality are also suggested to be very important to the durability and 

curing aspects of the surfacing (Asphalt Institute, 1994). Hence, the experiments had to 

investigate these aspects to understand material interactions, in order to select the viable 

polymer(s), bitumen, emulsifier, aggregate, and emulsion process method. 

1.5 Formulation Detailed Design 

The detailed design experiment took the best polymer, emulsifier, bitumen type, 

aggregate type and emulsion processing method determined from the initial formulation 

material screening. The emulsion was further investigated in detail by examining the 

effects of the polymer, emulsifier and emulsifier solution pH. These aspects were selected 

as they could affect in some way the emulsion stability, the bitumen resistance to 

deformation and also the microsurfacing cure rate. The aim was to refine the material 

addition levels to produce an optimal set of microsurfacing performance characteristics. 

To investigate the overall research questions a selection of experimental design trials 

were used to systematically examine the performance effects of materials and refine step 

by step the formulation to be ready for a mid-scale trial. 



4 

1.6. Confocal Microscopy Research 

Polymer modified bitumen should ideally have a microstructure that consists of a fine 

dispersion of polymer throughout the bitumen (Piazza et al., 1980; Bouldin et al., 1990; 

Morgan & Mulder, 1995; PIARC, 1999). But the addition of polymer to bitumen can 

cause compatibility problems in the polymer-bitumen blend. The problem can manifest 

itself as phase separation whereby the polymer rises to the top of the bitumen. Or the 

polymer can coagulate into lumps at a microscopic level giving an uneven distribution. 

This incompatibility is strongly dependent on the bitumen source (Morgan & Mulder, 

1995; Loeber et al, 1996). Incompatible binders can cause storage stability problems and 

also can result in early aggregate loss from a road surfacing. 

Microscopy techniques have been used in several studies to examine the compatibility of 

polymers with bitumen (Piazza et al., 1980; Bouldin et al., 1990; Loeber et al., 1996; 

Rozeveld et al. , 1997; Lu et al., 1999). But there has been no reported literature regarding 

the compatibility of polymers with New Zealand's source of bitumen at a microstructural 

level. Another gap in the research literature relates to the microstructure of polymer 

modified bitumen emulsion binder. The modified binder after evaporation of the water 

phase is supposed to result in the same properties of a hot sprayed modified bitumen 

(Asphalt Institute, 1994). The research investigates this effect, but also goes further and 

investigates the way that the polymer improves the properties of bitumen, and how they 

resist stress in the binder and microsurfacing. A technique called confocal microscopy 

was used to assess the binder and microsurfacing microstructure. 

Chapter 2 will cover the technical aspects of bitumen emulsions, polymer modification, 

and microsurfacing technology to give an overview to understand the critical parameters 

involved. 

The research has been partially funded by the Higgins Group of Companies and 

Technology New Zealand, and the formulations should be treated as confidential. 



5 

1.7 Research Aims and Objectives 

1.7.1 Aim 

The research aim is to investigate and develop a polymer-modified emulsion based road 

surfacing (microsurfacing) formulation to a mid-scale prototype stage. A supplementary 

part of the development was to investigate the polymer-bitumen interactions and how 

they affect the products end properties by using confocal microscopy. 

1.7.2 Research Objectives 

• Identify and measure the effects of polymers to meet the performance requirements of 

the microsurfacing. 

• Determine the required effect of emulsifiers and aggregate quality to obtain a rapidly 

curing microsurfacing. 

• Use a combination of qualitative (microscopy) and quantitative (physical testing) 

techniques to understand the performance enhancing properties of polymer-modified 

bitumen. 

• Compare and relate the test results of the modified bitumen binder and 

microsurfacing to results from overseas studies. 

• Measure and determine the effect of varying the method of adding the polymer to the 

emulsion. 

1.7.3 Research Constraints 

Product Constraints 

• 
• 

Bitumen sourced from Marsden Point refinery must be used . 

Meet relevant industry specifications for performance . 

Process Constraints 

• Prototype emulsions produced using the Higgins laboratory colloid mill. 



2.1 

2.2 

2.3 

2.4 

2.5 

2.6 

2.7 

2.8 

2.9 

2. REVIEW OF BITUMEN EMULSION SCIENCE, POLYMER 

MODIFICATION, AND MICROSURFACING TECHNOLOGY 

Introduction 

Bitumen Emulsification 

Advantages of Bitumen Emulsions 

Emulsion Classification 

Raw Materials 

2.5.1 Bitumen 

2.5.2 Emulsifiers 

2.5.3 Water 

2.5.4 Acids 

2.5.5 Additives 

Emulsion Production 

2.6.1 Stirring 

2.6.2 Homogenizers 

2.6.3 Colloid Mills 

2.6.4 Processing Variables 

Emulsion Formulation Characteristics 

2.7.1 Emulsion Stability 

2.7.2 Breaking Process 

2.7.3 Emulsion Adhesion 

2.7.4 Cohesion 

2.7.5 Viscosity 

Characteristics of General Emulsion Stability 

2.8.1 Low Interfacial Tension 

2.8.2 Zeta Potential 

2.8.3 Electrical Double Layer Repulsions 

2.8.4 Narrow Droplet Size Distribution 

2.8.5 High Viscosity 

Modification of Bitumen Emulsion Properties 

2.9.1 Increasing the Viscosity of the Emulsion 

6 

9 

9 

10 

11 

12 

12 

17 

19 

19 

19 

20 

21 

21 

22 

22 

23 

24 

25 

26 

26 

26 

27 

27 

28 

28 

28 

28 

28 

29 



7 

2.9.2 Decreasing the Viscosity of the Emulsion 29 

2.9.3 Changing the Emulsion Breaking Rate 30 

2.9.4 Storage Stability 30 

2.10 Polymer Modified Bitumen and Emulsions 32 

2.10.1 Polymer Modified Bitumen 32 

2.11 Types of Polymer Used 33 

2.11.1 Plastomers 33 

2.11.2 Elastomers 33 

2.12 Interactions during Manufacture 34 

2.12.1 Grade of Polymer 35 

2.12.2 Physical Form of Polymer 35 

2.12.3 Nature and Grade of Bitumen 35 

2.12.4 Mixing Equipment 35 

2.13 Elastomeric Polymers 36 

2.13. l Styrene Butadiene Styrene (SBS) 36 

2.13.2 Styrene Butadiene Rubber (SBR) 38 

2.13.3 Neoprene (Polychloroprene) 39 

2.13.4 Natural Rubber (Polyisoprene) 39 

2.14 Plastomeric Polymers 40 

2.14.1 Ethylene Methyl Acrylate (EMA) 40 

2.14.2 Ethylene Vinyl Acetate (EV A) 41 

2.15 Bitumen/Polymer Compatibility 42 

2.16 Microscopic Investigations of Bitumen/Polymer Blends 44 

2.17 Polymer Modified Emulsions 45 

2.18 Modified Emulsion Definitions 46 

2.19 Manufacturing Processes 46 

2.20 Polymer Modified Emulsion Properties 48 

2.20.1 Storage Stability 48 

2.20.2 Breaking Process · 49 

2.20.3 Choice of Bitumen 49 



8 

2.21 Microsurfacing Technology 50 

2.22 Irttroduction 50 

2.23 History and Relevance ofMicrosurfacing to New Zealand 50 

2.24 Manufacture ofMicrosurfacing 51 

2.25 Materials 52 

2.25.1 Polymer Modified Emulsion 53 

2.25.2 Aggregate 53 

2.25.3 Mineral Filler 54 

2.25.4 Water 54 

2.25.5 Additives 55 

2.26 Mix Design 55 

2.27 Rate of Application 56 

2.28 Weather Limitations 56 

2.29 Chapter Conclusions 56 



9 

2.1 INTRODUCTION 

The review consists of three parts. Firstly a review of bitumen emulsion science and 

technology, raw materials, and production. Secondly, the modification of bitumen 

emulsion properties and performance by addition of a polymer. The third part gives an 

overview of the micro surfacing pavement system that the modified emulsions are used in, 

and covers the design, raw materials and application of the surfacing. The reviews form 

the basis for understanding the product and its design, and assists in developing the 

product specifications and initial formulation guidelines. 

2.2 BITUMEN EMULSIFICATION 

Bitumen and water are immiscible under normal circumstances, but they can be 

emulsified to produce a homogeneous blend. Suspending bitumen particles in water by 

means of emulsifying and stabilising agents forms the emulsion. The size of the particles 

is typically in the range of I to 10 µm. Common bitumen contents of an emulsion vary 

depending on the application, but is usually between 55-75% for road sealing (Asphalt 

Institute, 1994). Bitumen is normally referred to as the dispersed phase or discontinuous 

phase while the water phase is referred to as the aqueous, soap, or continuous phase 

(Lissant, 1974). 

Emulsifying agents keep the bitumen droplets in stable suspension and controls the 

breaking time. The surfactant changes the surface tension at the bitumen/water interface; 

this permits the bitumen to remain in a suspended state. The particles, all having a similar 

electrical charge repel each other, which aids in their remaining in a suspended state 

(Asphalt Institute, 1994). Ionic emulsifying agents consist of a long hydrocarbon chain, 

which has an anionic or cationic functional group at one end. Figure 2-1 illustrates the 

orientation of the emulsifier on a bitumen droplet. 



Figure 2-1 Emulsifier Behaviour on a Bitumen Particle 

Bitwnen particle -------1111i~, Ionic group (positively or 
negatively charged) 
Hydrocarbon chain 

10 

The object of bitumen emulsions for road surfacing is to make a dispersion of the 

bitumen in water, stable enough for pumping, prolonged storage, and mixing. 

Furthermore, the emulsion should break down quickly after contact with aggregate in a 

mixer, or after spraying on the roadbed. Upon curing, the residual bitumen retains all of 

the adhesion, durability, and water-resistance of the original bitumen (Asphalt Institute, 

1994). 

2.3 Advantages of Bitumen Emulsions 

Bitumen emulsions have distinct advantages over heated bitumen and the use of solvent 

( cutback) bitumen (Asphalt Institute, 1994; Baker, 1996; Reed, 1996; Kala et al., 1999): 

1. Safety/ Energy conservation/ pollution control 

2. Versatility 

3. Performance 

Worker safety 

Emulsions are water based. They have no flash point, and are not flammable or explosive. 

They do not pose a serious health·risk to workers as hydrocarbon fumes are virtually 

eliminated, and they do not cause severe burns as they are generally applied cold or only 

heated to about 60°C, or 85°C for high residual spray grades of 68-80% bitumen (Transit, 

1994). 

Energy Conservation 

For cutback bitumen, the solvent is only added to reduce the viscosity of the bitumen to a 

level where it can be sprayed at a lower temperature. The solvent is expected to evaporate 

into the atmosphere, and if it does not, the bitumen will retain a lower softening point 



11 

long after being applied to the road. The use of emulsions can also generate a significant 

saving in fuel products such as kerosene, naphtha and diesel (Reed, 1996). 

Pollution control 

Because emulsions carry little if any solvents, hydrocarbon emissions, which lower air 

quality, are reduced. 

Versatility 

There are many different applications for emulsions such as spray chip sealing, slurry 

surfacing, microsurfacing, and other cold mixes. They can also be stored in drums for 

remote work. They can be used in all instances where hot bitumen is used. 

Performance 

• Improvement in adhesion to aggregates (better wetting, ability to mix well with wet 

aggregate, and binding is assisted by a physico-chemical process for cationic 

emulsions). 

• Extension of the range of conditions for emulsion application (sealing in marginal 

conditions). 

• Reduced energy costs. 

• Reductions in safety related downtime. 

• Reduced labour costs with heating. 

• Reduced material costs, particularly solvents and adhesion agents. 

2.4 Emulsion Classification 

Bitumen emulsions are divided into three categories: Anionic, cationic, and non-ionic. 

These classifications refer to the type of electrical charge that is induced around the 

bitumen particle. The first two types are primarily used in road surfacing, with the 

cationic the more favoured option as it has a greater affinity for a variety of solid surfaces 

and generally break and cure faster (Nealyon & Gillespie, 1994). Further classification is 

based on how quickly the bitumen will coalesce (reform to basic bitumen). These are 

rapid set (RS), medium set (MS), and slow set (SS) types (Asphalt Institute, 1994). An 

RS emulsion has little or no ability to mix with an aggregate, an MS is expected to mix 

with coarse but not fine aggregate, and an SS to mix with fine or sandy aggregate. 



12 

The letter 'C' is used in front of the emulsion type to denote a cationic. Anionic can be 

denoted with an 'A' at the front of 'RS', but the ASTM specification is to denote the 

emulsion as anionic or non-ionic if the 'C' is absent. Also numbers are used to indicate 

the viscosity range of the emulsion i.e. 1 or 2. An 'h' follows certain grades to imply 

harder base bitumen such as 80/100 pen has been used. An 's' indicates that additional 

solvent has been added to the emulsion. 

Example: cationic rapid set, of viscosity rating 1, and hard grade of bitumen (CRS-lh). 

2.5 Raw Materials 

Basic bitumen emulsions generally consist of five main materials; bitumen, emulsifier, 

water, acid or alkali, and additives. 

2.5.1 Bitumen 

Bitumen is a complex material, but can be defined as a black cementitious hydrocarbon 

material that is naturally occurring or refined from crude oil (Holleran, 1994). All 

bitumen show a visco-elastic behaviour, their resistance to deformation being dependent 

on both the temperature and time during which a force is applied. Only under extreme 

conditions does a bitumen behave as either a typical elastic solid (low temperature very 

short loading time) or as a viscous liquid (high temperature, long loading time). Under 

normal temperature conditions, both viscous and elastic behaviour occurs (Whiteoak, 

1990). The common commercially available type of bitumen is petroleum bitumen. The 

bitumen consists of colloidal dispersed hydrocarbons in crude petroleum and is obtained 

by refining petroleum crudes. In New Zealand petroleum crude is refined at Marsden 

Point to produce the bitumen used for road sealing purposes. It is the residue from the 

vacuum distillation tower at the refinery (Transit, 1993). 

Bitumen contains a combination of the following three arrangements by which the carbon 

atoms are linked with each other (Whiteoak, 1990): 

1. Straight or branched chains. Bitumen of this type are referred to as "aliphatic" or 

"paraffinic". 



u 

2. Simple or complex saturated rings. "Saturated" means the highest possible 

hydrogen/carbon ratio in the bitumen molecules. These bitumen are often referred 

to as "naphthenic" types. 

J. One or more stable six-carbon condensed unsaturated ring structures (benzene, 

naphthalene). Normally referred to as "aromatic". 

Naphthenic bitumen have higher acid values than paraffinic types (West, 1985). Middle 

Eastern bitumen used in New Zealand usually has a low acid value and high salt content, 

making emulsification in particular more difficult with the paraffinic nature of the 

bitumen. The precise composition of the bitumen varies depending on the crude source, 

the manufacturing process, and subsequent ageing in service (Holleran, 1994 ). 

Bitumen can be separated into four chemical types called saturates, aromatics, resins and 

asphaltenes by the chemical n-heptane. A schematic is shown in Figure 2-2. 

Figure 2-2 Main Chemical Constituents of Bitumen 

n-heptanlnso lub !es 

I Asphaltenes I 

n-heptanl solubles 

.-------1 Maltenes 1-------. 

saturates aromatics res111S 

2.5.1.1 Asphaltenes 

Asphaltenes are high molecular weight fractions that are insoluble in n-heptane. They 

form highly condensed systems, are highly polar and interact strongly (Whiteoak, 1990). 

They are black or brown amorphous solids and constitute 5% to 25% of the bitumen. 

Molecular weights of asphaltenes tend to range from 1,000 to 100,000 (Whiteoak, 1990). 

But, this seems to be a large variation in molecular weight. The asphaltenes content has a 

large effect on the rheological characteristics of bitumen. Increasing the asphaltenes 



content produces a harder, higher viscosity bitumen with a lower penetration, and higher 

softening point (Whiteoak, 1990; Rozeveld et al., 1997). 

2.5.1.2 Maltenes 

Maltenes are n-heptane solubles. They are often categorised as resin and oil fractions 

(Whiteoak, 1990). 

Resins 

Are dark brown in colour, solid or semi-solid, and are very polar in nature. This makes 

them strongly adhesive. They react as dispersing agents or peptizers for the asphaltenes 

and the proportion of resins to asphaltenes determines to a degree the solution (Sol) or the 

gelatinous (Gel) characteristics of the bitumen (Roberts et al., 1991). The molecular 

weight varies from 500 to 50,000 (Whiteoak, 1990). 

Oil Fraction 

Further categorised as aromatics and saturates. 

Aromatics 

Aromatics are the lowest molecular weight naphthenic aromatic compounds. They are 
-, 

non-polar but can be polarised. Aromatics make up the major portion of the dispersion 

medium for the peptised asphaltenes. They constitute 40 to 65% of the total bitumen and 

are dark brown viscous liquids. Average molecular weight ranges between 300 to 2,000 

(Whiteoak, 1990; Loeber et al., 1998). 

Saturates 

Are non-polar straight chain and branched paraffins, and alkyl naphthenes. They are 

viscous oils and straw or white in colour. The average molecular weight is 300 to 2,000, 

and compounds include waxy and non-waxy saturates. The fraction makes up about 5% 

to 20% of the bitumen, and contributes to the viscous nature of bitumen (Whiteoak, 1990; 

Rozeveld et al., 1997). 

The constituents have a major effect on the suitability of the bitumen for road sealing, 

and for improved modification of the bitumen properties such as _ polymer additives or 



·I 

bitumen emulsification (Piazza et al., 1980; Whiteoak, 1990; Resp & Woodhams, 1992; 

Loeber et al., 1998; Lu et al., 1999). In particular, asphaltene levels above 12% lead to 

emulsion and polymer modification problems (Bouldin et al., 1991 ; Brule, 1995; 

Holleran & Reed, 1999). 

2.5.1.3 New Zealand's bitumen constitution 

Safaniya Bitumen 180/200 pen (Herrington, 1999): 

Asphaltenes 

Aromatics 

Resins 

Saturates 

14.8% 

11.2% 

45.0% 

29.0% 

The aromatic content of 11.2% is considerably less than the typical range proposed by 

Whiteoak ( 1990) and Lu et al.( 1999). The saturates content of 29% is also considerably 

higher. The saturates fraction decreases the ability of the maltenes to disperse the 

asphaltenes and high saturates fractions can lead to increased agglomeration of the 

asphaltenes (Domke, et al. , 1999). 

Colloidal Index 

Loeber et al. (1998) propose that the bitumen constituents can be expressed as the 

colloidal index (Cl) . 

CI = dispersed constiuents 
Flocculated constituents 

= aromatics + resins 
saturates + asphaltenes 

(1) 

A higher colloidal index (greater than 2.5) means the asphaltenes are more peptised 

( dispersed) in the oil based medium. Loeber et al. ( 1998) concluded that a low colloidal 

bitumen has a connected network structure. Whereas, higher colloidal bitumen is made of 

individual domains of asphaltene particles which results in bitumen that is more stable 

when modified (Lu et al., 1999). The presence of resins appears necessary to obtain well­

dispersed suspensions, whereas if absent, flocculation takes place and leads to less 

homogeneous bitumen. Increasing the asphaltene level leads to a more flocculated system 

and increasing bonds between particles. A network structure will be formed with more 



16 

elastic behaviour and higher stiffness. Increasing the aromatic oil content leads to a more 

dispersed and viscous system The addition of resins homogenise bitumen as they peptise 

the asphaltenes by forming smaller asphaltene micelles. This indicates that a higher 

colloidal index is preferable for emulsifying bitumen, as smaller asphaltene micelles will 

be present because they are better dispersed in the oil phase. The colloidal index of the 

Safaniya bitumen is 1.3, which is quite low and indicates that stability problems may 

occur with emulsification, as the asphaltenes will not be well dispersed by the oils. 

Resins/Asphaltene Effects 

The work by Salou et al. (1998) assessed the stability of bitumen emulsions using the 

Resins/ Asphaltenes ratio (r/a ratio). They contend that a bitumen with a high r/a ratio . 

(>3.0) will disperse better in acid water. A high resin content seems to facilitate the 

migration of the natural surfactants at the bitumen-water interface. They observed that 

high r/a ratios tended to give stable emulsions, whereas lower r/a ratios give unstable 

emulsions. The proposed reason for this is that the higher r/a ratio results in a different 

distribution of the bitumen polar species at the bitumen-acid water interface during 

emulsion manufacturing. The Safaniya bitumen that New Zealand uses has a r/a ratio of 

3.0 and this indicates that relatively stable emulsions are possible with this bitumen. This 

result conflicts with that of the colloidal index which indicates that stable emulsions may 

be difficult. This indicates that there could be other factors having an effect, or that the 

relationships used are not very reliable and should be treated with caution. 

2.5.1.4 Bitumen Manufacture and Grades 

The sources of crude oil have different levels of the vanous constituents and a 

comparison of bitumen is held in Appendix 2-1 . It highlights the great variation that is 

possible with different crude sources, even those from the same country, and how the 

bitumen properties vary accordingly. New Zealand's source of bitumen is from the 

Persian Gulf (Saudi Arabia - Safaniya Crude). Bitumen from different processing routes 

will also have a different final rheology (Herrington, 1993; Holleran, 1994). Bitumen 

produced at Marsden Point is by the straight run method and is hardened by 

propane/butane precipitation (Transit, 1993; Pidwerbesky, 1999). 



17 

Penetration Grade Bitumen 

Bitumens are available as various types and grades. Bitumen is produced in New Zealand 

in two grades 44/55 pen and 180/200 pen. Typical paving grades used by civil 

engineering contractors are 80/100 and 180/200, with the 80/100 grade a blend of 44/55 

and 180/200 penetration bitumen. Penetration grade bitumen are specified by penetration 

and softening point. Penetration is a measurement of the hardness of the bitumen grade. It 

is measured by a needle of specified dimensions allowed to penetrate into a sample of 

bitumen, under a known load ( 100 g), at 25°C, for 5 seconds. The distance the needle 

penetrates, in decimillimetres ( dmm) is termed the penetration (Whiteoak, 1990). The 

greater the penetration the softer the bitumen. An 80/100 pen bitumen has a penetration 

of90 ± 10 i.e. 80 - 100. 

2.5.2 Emulsifiers 

In bitumen emulsions, surface-active chemicals (emulsifiers), are water-soluble 

substances that profoundly change the, properties of the solvent and the surfaces they 

contact. They are defined according to the manner in which they dissociate or ionise in 

water, and are characterised structurally by having a lipophilic, hydrocarbon "tail" and a 

polar hydrophilic "head" (Dybalsk~ 1985; Reed, 1996). 

Surface active agents in bitumen emulsification owe their physico-chemical behaviour to 

their property of being absorbed at the interface between liquids and solids phases. They 

tend to concentrate in an oriented manner, at the interface, so that they tum a majority of 

their hydrophilic groups toward the more polar phase and most of their lipophilic groups 

away from the polar phase. The surface-active molecule acts as a bridge between two 

phases (Asphalt Institute, 1994). 

Cationic emulsions possess a positive electro-chemical charge, which is imparted to the 

bitumen at the time of emulsification. Cationics are based on acid salts of amines 

prepared from fatty acids. Examples are fatty diamines, imidazolines, amidoamines, and 

quaternary ammonium compounds. Figure 2-3 shows a diagram of the structure of a 

cationic molecule where the hydrocarbon chain is about 16-19 carbon units long (Reed, 

1996). The fatty amines are converted into a water-soluble salt form by reacting with an 

acid, most often hydrochloric (HCl), but H2S04 , HN03, Acetic acid, and sometimes 



18 

H3PO4 are used. The quaternaries are usually water-soluble as produced and do not 

require an acid (Reed, 1996). 

The reaction to produce the amine salt is shown below: 

R-NH2 + HCI R-NH3+ +c1 · 

Fatty amine + hydrochloric acid --->~ Amine hydrochloride 

Figure 2-3 Cationic Emulsifier 

CH 2-- CH_ 

/~/~ 
16 - 19 units .. CH CH > 

Non-polar Tail Polar Head 

2.5.2.1 Cationic slow set (CSS) emulsifier characteristics 

These emulsifiers are used for slurry surfacing mixes due to the slow setting nature of the 

emulsifier allowing sufficient mixing with fine aggregate before setting. Slow set 

emulsifiers usually contain cyclic hydrocarbon groups, such as lignin, and rosin 

derivatives. These "bulky" emulsifiers are unable to orient themselves in orderly close­

packed molecular films around the emulsion droplets. They tend to stabilise the emulsion 

by clumping together as aggregates that act as barriers between the bitumen. The 

emulsifier concentrations required are generally above the critical micelle concentrations 

and serves to explain the usual ability of CSS emulsions to withstand high dilution with 

water together with good stability retention (Lissant, 1974). 

2.5.2.2 Emulsifier concentration and solution pH 

Low and medium setting emulsifiers tend to be 0.8 - 1.5% of the total emulsion and 

require a soap solution pH of normally 2.0 - 7.0 (Holleran & Reed, 1999). Emulsifier 

levels above 1.5% tend to result in free emulsifier in the water phase, which is not 



19 

absorbed onto the bitumen. Instead the free emulsifier will be absorbed more quickly 

onto the surface of the aggregate than the bitumen, and this modifies the surface charge 

of the aggregate and reduces its reactivity to the bitumen droplets. The result is a slower 

rate of cohesion development in cold mix surfacings (Engman et al., 1998). 

2.5.3 Water 

Water wets, dissolves, adheres to other substances, and it moderates chemical reactions. 

These aspects are important to producing a good emulsion (Asphalt Institute, 1994). 

Water can adversely affect emulsion properties because of impurities, either in solution or 

colloidal suspension. The presence of ions is the main factor concerning water quality for 

emulsions (Dybalski, 1985). Calcium and magnesium ions assist in making a more stable 

cationic emulsion, whereas the presence of phosphate and carbonate ions form insoluble 

salts with amine hydrochlorides present in cationic emulsifiers (Clark, 1998). The water 

supply used for production purposes at Higgins is artesian bore water generally higher in 

magnesium ion concentrations, although there are no figures available. 

2.5.4 Acids 

Acids are used to 1omse cationic heads of emulsifiers to allow dispersion in water. 

Hydrochloric acid is most commonly used in the industry (Whiteoak, 1990) but other 

acids such as phosphoric, and acetic acid are sometimes used. Acidity and pH can have a 

major impact on emulsion properties such as settlement and binder cohesion and is 

therefore a key factor to be controlled during production. 

2.5.5 Additives 

Various additives can be added to an emulsion to improve certain performance aspects, 

and are listed below (Whiteoak, 1990): 

• Kerosene - small amounts can reduce the tendency of bitumen with high specific 

gravity to settle, but increases the emulsion viscosity and softens the bitumen. 

• Salts - such as calcium chloride can be added in very small amounts to also reduce 

settlement by increasing the specific gravity of the aqueous phase. They also reduce 

the surface tension of the water. But, too much will destabilise the emulsion causing 

early breaking (Menon & Wason, 1988). 



20 

• Polymers - Addition of thermoplastic polymers reduce the bitumen temperature 

susceptibility allowing better performance at higher and lower temperatures, and 

increases the strength of the bitumen to help resist deformation. 

2.6 Emulsion Production 

The production of a bitumen emulsion involves the preparation of the emulsifier solution 

and the bitumen phase. The cationic emulsifier is generally mixed with a percentage of 

the total water that has acid added and is heated to aid dispersion of the emulsifier. Once 

the concentrate is thoroughly mixed the remaining water is added and the pH adjusted to 

the required level with further acid. Other additives such as a salt or latex polymer can 

also be added to the aqueous phase. 

Bitumen makes up the dispersed phase and is known as the binder. The two streams are 

fed separately but simultaneously into a blender or mill device to form the emulsion. A 

schematic diagram of the production process is shown in Figure 2-4. 

Figure 2-4 Schematic Diagram of an Emulsion Production Process 

Water 
Steam_~ 

Emulsifier 

Aqueous Phase Tank 

Flow Control 

Colloid Mill 

Acid Additive 

Bitumen 

Flow Control 

Emulsion Storage 



21 

There are several devices available to produce an emulsion (Walstra, 1983). The key 

types of devices are listed as follows: 

1. Stirring (high speed Silverson mixer) 

2. Homogenizers 

3. Colloid mill 

2.6.1 Stirring 

High-speed blenders such as Silverson mixers are more commonly used for forming 

emulsions in the food industry (McClements, 1999) but have been used to produce 

bitumen emulsions in several laboratory studies and patents (Sabbagh & Lesser, 1998; 

Al-Sabagh et al., 1997; European Patent 561472Al). But, there have been no references 

found that refer to any large industrial scale manufacture using high-speed mixers. The 

rapid rotation of the stirring blade generates a combination of longitudinal, rotational, and 

radial velocity gradients in the liquids which disrupts the interface between the oil and 

water, causing the liquids to become intermixed, and breaks down the larger droplets. 

The average droplet size typically produced in high-speed blenders is about 2 to 10 µm in 

diameter (McClements, 1999). 

2.6.2 Homogenizers 

In a homogenizer the liquid streams are brought under high pressure by a positive pump 

and are forced through a narrow adjustable valve slit ; due to the pressure, the valve opens 

against a spring and the liquids obtain a high velocity. The combined liquids experience a 

combination of intense shear, cavitational, and turbulent flow conditions and cause the 

larger droplets to be broken down into smaller ones. The residence time of the emulsion 

in the homogenizer is less than 0.1 ms and the method is more efficient at emulsifying 

liquids with a viscosity less than 1,000 centipoise ( cP) (McClements, 1999). 

Homogenizers are more effective at reducing the size of pre-existing coarse emulsions 

prepared by blending than by creating an emulsion from two separate liquid phases. A 

minimum droplet size of 0.1 µm can be produced with the method. High-pressure 

homogenizers are most commonly used in the food industry for producing fine emulsions 

and no literature has been found that indicates the use of the method for bitumen 

emulsions. Possible reasons are that the bitumen phase is usually of a viscosity of about 



22 

200 cP and makes the method less efficient than colloid mills (Walstra, 1983; 

McClements, 1999) and the residence time of the emulsion may be too quick to allow 

adequate coating of the bitumen droplets with emulsifier. 

2.6.3 Colloid Mills 

The general method of emulsification using a colloid mill involves concurrent streams of 

molten bitumen and soap solution directed by pumps into the intake of the colloid mill. 

The materials flow through a narrow gap between two disks: the rotor (a rotating disk) 

and the stator (a static disk). The rapid rotation of the rotor generates a shear stress in the 

gap, which causes the larger droplets to be broken down into smaller ones. The intensity 

of the shear stresses can be altered by varying the thickness of the gap between the rotor 

and stator (from about 50 to 1000 µm), and varying the rotation speed (from about 1,000 

to 20,000 rpm) (Whiteoak, 1990; McClements, 1999). The individual droplets of bitumen 

are coated with the emulsifier, which gives the surface of the droplets an electrical 

charge, and the resulting electrostatic forces prevent the droplets from coalescing. Colloid 

mills are extensively used for producing bitumen emulsions for the roading industry and 

Higgins have a laboratory sized Charlotte G-3 colloid mill and a full size G-75 mill at the 

Napier production facility. A bitumen emulsion can be passed through a colloid mill a 

.( second time to produce a finer particle size; and has been performed by Holleran (1995) 

and Hermadi & Strirling (1998). But this process is not seen as economic in the industry. 

The rest of the production and processing review aspects of bitumen emulsions relates to 

the colloid mill method of production. 

2.6.4. Processing Variables 

There are several processing variables that are important in the production of bitumen 

emulsions (Whiteoak, 1990; Durand, 1994): 

1. Rotational speed of colloid mill 

2. Gap between rotor and stator 

3. Mill pressure 

4. Temperature of both phases before emulsification 



2J 

2.6.4.1 Rotational speed and mill gap 

Both of these variables contribute to shear rate variation in the gap of the colloid mill. 

The higher the shear rate the smaller the particles created and a less polydisperse particle 

size distribution. This can influence product characteristics such as emulsion viscosity 

and storage stability. The gap setting is usually between 0.17 to 0.50 mm and this creates 

an emulsion with an average bitumen particle size between 1 to 10 µm (Asphalt Institute, 

1994). 

2.6.4.2 Mill pressure 

Colloid mills typically operate at atmospheric pressure but they can be operated above 

atmospheric pressure by increasing pressure on the exit line. This can result in a 

decreased particle size and more stable emulsions (Durand, 1994). Also bitumen contents 

of greater than the theoretical limit of 74% can be achieved this way. Mills operated 

under pressure require a heat exchanger to cool the emulsions below 100°C to avoid 

evaporation and coalescence. The Higgins colloid mills both operate at atmospheric 

pressure. 

2.6.4.3 Temperature of both phases before emulsification 

The viscosity of the bitumen should not exceed 200 cP and the typical temperature 

required to achieve this is 100°C to l 50°C. A higher bitumen temperature will produce a 

lower bitumen viscosity and a smaller particle size (Whiteoak, 1990). 

The soap phase temperature is partially dependent on the temperature at which the 

emulsifier will disperse and the resulting emulsion exit temperature. Soap temperatures 

between 30°C to 60°C are typical. 

The exit temperature is directly controlled by the two phases entering the mill. Exit 

temperatures above 92°C can lead to coalescence of the emulsion and typical exit 

temperatures for emulsions with 60% to 65% bitumen contents are 78°C to 85°C. 

2.7 Emulsion Formulation Characteristics 

The end use of the bitumen emulsion determines its main properties. But in general the 

emulsion should be mechanically stable to facilitate storage, handling and transport 



L4 

without significant deterioration in dispersion quality. The chemical stability of the 

emulsion varies depending on the type of aggregate it is to be mixed with. or how quickly 

it is required to break after application. Emulsion viscosity is critical as it determines the 

method and thickness of application to the substrate concerned. The key properties of the 

emulsion are summarised as (Hulshof, 1985; Whiteoak, 1990; Reed, 1996): 

1. The stability of the emulsion; 

2. The breaking process; 

3. The adhesion of the emulsion; 

4. The cohesion development; 

5. The viscosity of the emulsion. 

2.7.1 Emulsion Stability 

The stability of the emulsion involves storage stability and in particular its settlement or 

sedimentation, flocculation, and coalescence (Whiteoak, 1990). 

2.7.1.1 Storage stability 

The storage stability of the emulsion is initially indicated by the settlement of the 

emulsion, resulting in a bitumen lean upper layer and a bitumen rich lower layer. 

Settlement occurs as a result of gravity acting upon the denser discontinuous bitumen 

droplets. The velocity of the downward movement of the droplets can be estimated by 

Stokes Law, which states the settlement velocity (V) as (Whiteoak, 1990): 

V= 2Gr\p, - p2) 
9T] 

Where G = Gravitation acceleration (rns-2
) 

r = Particle radius (m) 

T] = Viscosity of continuous phase (kg m·1s" 1
) 

p, = Density of dispersed phase (kgm-3
) 

P2 = Density of continuous phase (kgm-3
) 

(2) 



25 

In addition to gravity, repulsive and attractive forces act upon the emulsion. Repulsive 

forces occur between the electrostatic double layers on the droplets created by the ionised 

emulsifier. The attractive force is associated with the mass of the droplets (Whiteoak, 

1990). If the droplets are large, or if the distribution of particle sizes is wide, the attractive 

force becomes a repulsive force. The sedimentation of an emulsion determines how long 

it may be stored. This is particularly important if the emulsion is to be stored for any 

lengthy period of time. 

2. 7.1.2 Flocculation 

After settlement bitumen droplets agglomerate into clumps creating a floe, this is referred 

to as flocculation (Whiteoak, 1990). At this stage the process is reversible and the flocks 

can be broken up by gentle agitation. 

2.7.1.3 Coalescence 

The coalescence of flocculated particles is a function of the surface charge and factors 

such as shearing and temperature. This stage is irreversible, in which the flocks fuse 

together to form larger globules. These globules are no longer able to be held in solution 

and settle out. When this occurs throughout the emulsion the emulsion is deemed broken, 

which is visually characterised by a colour change from brown to black. 

2.7.2 Breaking process 

The emulsion contains emulsifier molecules in both the water phase and on the surface of 

the bitumen droplets. The ions around the droplet are attracted to the negative ions on the 

aggregate surface, which weakens the charge on the surface of the droplets, which 

initiates the breaking process. A point is then reached where the charge on the droplets is 

so depleted that rapid coalescence takes place and the bitumen is liberated to adhere to 

the aggregate. The effects of pavement temperature, air temperature, humidity, emulsifier 

type, aggregate type, and wind also affect the breaking process ( Asphalt Institute, 1994 ). 

The cure of the emulsion film is the development of mechanical properties of the 

bitumen. A continuous film holds the aggregate in place with a strong adhesive bond. The 

cure rates are dependent on the water content, rate of evaporation and the diffusion of 

water through the curing binder (Holleran, 1999). 



2.7.3 Emulsion Adhesion 

Adhesion is the capacity to provide both the wetting of the aggregate surface by the 

binder and its bonding to the mineral surface and the base pavement (Chazel & L()zier, 

1999). A prime requirement is that bitumen 'wets' the surface to create a maximum 

contact area. With dry substrates the 'critical surface tension of wetting' of the aggregate 

is usually high enough to ensure that the bitumen spreads easily over the surface. 

However, with damp aggregate, the 'wetting' can only occur if the balance of the 

interfacial energies favours wetting by the bitumen. Cationic emulsifiers provide 

immediate bonding between the aggregate and the binder due to their chemical affinity 

(Nealyon & Gillespie, 1994). 

2. 7.4 Cohesion 

The cohesion of the binder is its capacity to withstand forces, which tend towards internal 

breaking of the binder (Chazel & Lozier, 1999). Cohesion should develop in a pavement 

mix after the emulsion has broken and the bitumen has formed an adhesive bond to the 

aggregate. Development of early cohesive strength is particularly important as it enables 

a pavement surfacing to be opened to traffic as soon as possible. The type and 

concentration of emulsifier have a major influence on the cohesion development. 

Overall, the quality of the bond between the bitumen and aggregate depends on the 

following factors (Whiteoak, 1990; Asphalt Institute, 1994; Glet, 1999): 

1. The type and amount of emulsifier; 

2. The bitumen grade and constitution; 

3. The pH of the emulsifier solution; 

4. The particle size distribution of the emulsion; 

5. The aggregate type and cleanliness. 

2.7.5 Viscosity 

The viscosity is important because the majority of emulsions are applied in the form of a 

spray, particularly for chip sealing in New Zealand (Transit, 1994). The distribution of an 

emulsion from a spray bar is a function of the viscosity of the emulsion. Additionally for 

slurry or Microsurfacing systems the viscosity must be high enough to prevent runoff 



'[/ 

from the aggregate and prevent settlement problems, but must not be too high or mixing 

problems can occur. 

2.8 Characteristics of General Emulsion Stability 

The following factors favour emulsion stability (Shaw, 1992; Salou et al., 1998; Holleran, 

1999): 

1. Low interfacial tension 

2. Zeta Potential 

3. Electrical double layer repulsion' s 

4. Narrow droplet size distribution 

5. High viscosity 

2.8.1 Low Interfacial Tension 

The adsorption of surfactant at oil-water interfaces causes a lowering of interfacial 

energy, therefore facilitating the development and enhancing the stability of the large 

interfacial areas associated with emulsions. In emulsion manufacture, aromatics and 

resins have a lower interfacial tension (IFT) with water than asphaltenes and saturates. 

This is possibly due to the increased polarity of the aromatics and resins as they have an 

increased affinity with the polar aqueous phase, hence reducing IFT (Al-Sabagh et al,. 

1997). This seems to indicate that increasing the aromatics and resins content of the 

bitumen results in an increased stability of its emulsion with water. Comparing the 

aromatic and resins content of the bitumen used by Al-Sabagh et al. ( 1997) and New 

Zealand ' s bitumen gives the fo !lowing result: 

Aromatic-Resin content (Al-Sabagh) = 82.3% 

Aromatic -Resin content (New Zealand)= 56.2% 

The difference is 26%, and possibly indicates that the bitumen used in New Zealand is 

not entirely suitable for producing emulsions that are stable to flocculation and 

coalescence effects without the aid of additives or increased emulsifier levels to help 

lower the interfacial tension. To a certain extent this phenomenon has been observed in 

emulsions that Higgins have produced and high settlement results are common. 



2.8.2 Zeta Potential 

Zeta Potential is the electrical potential between the surface of the bitumen particle and 

the bulk solution. The emulsifier adsorbed onto the surface of the bitumen determines 

zeta potential. The form of the double layer around the bitumen droplet depends on the 

concentration and ionic density of the emulsifier and the pH. A large zeta potential 

indicates a greater double layer, faster movement and greater repulsion between particles . 

. Larger repulsiorls produce stable emulsions (Reed, 1996). Zeta potential for cationics 

range from +128 millivolts (mv) to +18 millivolts (mv) (West, 1985). 

2.8.3 Electrical Double Layer Repulsions 

Inter-particle repulsion due to the overlap of similarly charged electric double-layers is an 

important stabilising mechanism in o/w emulsions (Shaw, 1992; Holleran, 1999). When 

ionic emulsifying agents are used, a lateral electric double layer repulsion can prevent the 

formation of a close packed film. This film-expanding effect can be reduced by using a 

mixed ionic plus non-ionic film and/or increasing the electrolyte concentration in the 

aqueous phase (Reed, 1996). 

2.8.4 Narrow Droplet Size Distribution 

Larger droplets are less unstable than smaller droplets due to their smaller area-to-volume 

ratio, and will tend to grow at the expense of the smaller droplets. If this continues, the 

emulsion eventually breaks. Emulsions with uniform droplet sizes are less prone to this 

effect. 

2.8.5 High Viscosity 

A high Newtonian viscosity retards the rates of creaming, settlement, and coalescence. 

However, the overall rheological properties of a viscous emulsion may not be acceptable, 

such as causing difficulty in mixing. The end product use of the emulsion must be 

considered in the formulation. 

2.9 Modification of Bitumen Emulsion Properties 

The basic properties of an emulsion such as viscosity, storage stability, breaking rate and 

particle size distribution can be modified by (Whiteoak, 1990): 



29 

• Changing the grade, concentration or origin of the bitumen; 

• Changing the emulsion formulation; 

• Changing the type of emulsifier and/or its concentration. 

2.9.1 Increasing the Viscosity of the Emulsion 

Increasing the bitumen content, modifying the aqueous phase, increasing the mill flow 

rate, and decreasing the bitumen viscosity can increase the viscosity of an emulsion. 

Increasing the bitumen content 

Bitumen concentrations over 65% induce a rapid increase in viscosity which can help 

minimise settlement of the emulsions, and prevent run-off on application to the road 

surface. But a higher viscosity can severely reduce spraying performance. But this is not 

applicable for slurry or microsurfacing systems, as the bitumen content is limited to 60% 

to 65%. 

Modification of the aqueous phase 

Decreasing the acid content, or increasing the emulsifier content can mcrease the 

viscosity. 

Increasing the flow rate through the colloid mill 

At bitumen contents below 65% the viscosity is virtually independent of flow rate 

(Whiteoak, 1990). But at higher levels the bitumen droplets are packed more closely, 

inducing a change in the particle size distribution and increasing the viscosity. 

Decreasing the viscosity of the bitumen 

Lowering the bitumen viscosity before it enters the mill reduces the particle size of the 

emulsion and tends to increase the viscosity of the emulsion. 

2.9.2 Decreasing the Viscosity of the Emulsion 

To reduce the viscosity the following changes can be made (Whiteoak, 1990): 



30 

• Reduce the bitumen content. But this results in the need to apply a greater amount of 

emulsion (which increases costs) to achieve the same residual bitumen coverage as 

cutback bitumen. 

• Decrease the flow rate through the colloid mill. 

• Modify the emulsification formula. By increasing the acid content, or decrease the 

amine content. But must keep in mind that the aqueous phase properties have a large 

effect on the other emulsion properties. 

2.9.3 Changing the Emulsion Breaking Rate 

The breaking rate is strongly dependent on the aggregate type and size distribution; but 

other modifications are (Dybalski, 1985; Whiteoak, 1990): 

Modify the aqueous phase composition 

The breaking rate of the emulsion can be increased by reducing the acid content, 

increasing the emulsifier content or by decreasing the ratio between the acid and 

emulsifier contents. 

Increasing the bitumen content 

An increase in the bitumen content increases the breaking rate of the emulsion; the rate of 

increase is dependent on the aqueous phase composition. 

Other parameters 

Additional influences on the breaking rate are: 

• Type of emulsifier used; 

• Particle size distribution, the finer the particle size the smaller the dispersion the 

slower the breaking rate; 

• Temperature, the higher the ambient temperature the faster the breaking rate of the 

emulsion (faster evaporation of water from the emulsion). 

2.9.4 Storage Stability 

A deficiency in the storage stability of an emulsion usually appears in the form of 

settlement for which there are several causes (Whiteoak, 1990; Holleran, 1999): 

C 



31 

Bitumen Specific Gravity 

Bitumen with high specific gravity will tend to settle when emulsified. The problem can 

be reduced by: 

• Adding kerosene to the bitumen before emulsification to reduce the specific gravity, 

this will however result in an increased emulsion viscosity and a reduced viscosity of 

the binder on the substrate. 

• By increasing the specific gravity of the aqueous phase by the addition of a salt such 

as calcium chloride. 

Emulsion Viscosity 

Low viscosity emulsions are more prone to settlement than high viscosity emulsions · 

because the particles have more freedom to move. But if the viscosity is increased too 

much the emulsion will not spray evenly for chip sealing operations. But a higher 

viscosity is not too critical for applications such as slurry sealing or rnicrosurfacing. 

Electrolyte content 

The presence of electrolytes m the bitumen . can reduce the storage stability of an 

emulsion. In cationic emulsions a high sodium concentration can induce premature 

breaking during storage (Dybalski, 1985). This can be counteracted by the addition of a 

salt to the aqueous phase. 

Particle Size Distribution 

The size distribution of the emulsion droplet is dependent on the interfacial tension 

between the bitumen and aqueous phase (a lower interfacial tension results in the bitumen 

dispersing easier) and on the energy used in dispersing the bitumen. For a given 

mechanical input, harder bitumen (80/100 pen or less) will produce coarser emulsions, 

and high penetration ( 180/200) or cutback bitumen finer emulsions. Bitumen emulsions 

with a broad spectrum of particle sizes are more prone to settlement than those with a 

narrow size distribution (Tausk & Wilson, (1981); Holleran, 1999). This is due to large 

particles settling more quickly because of the repulsion forces between the particles. 

Hence, emulsions with a relatively narrow particle size distribution are more storage 

stable. 



32 

2.10 POLYMER MODIFIED BITUMEN AND EMULSIONS 

2.10.1 Polymer Modified Bitumen 

The limits of mechanical stability of road surfacing are often exceeded and this results in 

damage such as cracking and deformation. To control these problems, road surfacing 

requrres: 

• Better resistance to fatigue, 

• Increased resistance to permanent deformation, 

• Greater flexibility at low temperatures, 

• Higher resistance to stone loss and abrasion, 

• Adequate resistance to ageing. 

To obtain these performance characteristics, modification of the bitumen's basic 

properties is needed. Polymers are ideal bitumen modifiers because (Exxon, 1996): 

• Polymers and bitumen are basically compatible, as they are both largely polar 

materials. 

• Polymers can be engineered to provide specific characteristics. 

• Polymers added to bitumen result in a material with hybrid characteristics - a bitumen 

composite. 

Improvements made by usmg polymers to modify bitumen include (Exxon, 1996; 

Morgan & Mulder, 1995): 

• Increasing the viscosity of the binder in service, 

• Reducing the thermal susceptibility of the binder, 

• Widening the range of plasticity, 

• Increasing the cohesion of the bitumen, 

• Increasing the resistance to permanent deformation, 

• Improving the resistance to fatigue at low temperatures, 

• Improving binder-aggregate adhesion, 

• Slowing down the ageing process of bitumen. 



33 

2.11 Types of Polymers Used 

There are two types of polymers used to modify the properties of bitumen: 

1. Plastomers - normally based on ethylene copolymers. Examples are Ethylene Vinyl 

Acetate (EV A), Ethylene Methyl Acrylate (EMA). 

2. Elastomers - normally consisting of styrene-block copolymers. Key examples are 

Styrene Butadiene Rubber (SBR), Styrene Butadiene Styrene (SBS), Neoprene, and 

Natural Rubber 

2.11.1 Plastomers 

Are based on random copolymers of ethylene. They are rigid polymers due to their 

hydrocarbon backbone and provide stiffness to the bitumen. Plastomers are generally 

referred to as semi-crystalline polymers. This means that there is a degree of regularity in 

the molecular structure. Plastomers can be classed by their melt transition temperatures 

(Tm), which means the temperature at which crystalline elements such as ethylene go 

from a solid to a liquid state (PIARC, 1999). Plastomers provide good low temperature 

resistance to cracking. 

2.11.2 Elastomers 

Elastomers can be stretched to many times their original length and return back to their 

original shape without permanent deformation. They are amorphous polymers, meaning 

that they do not exhibit any structural order. Their arrangement of molecules tangle 

around each other in a jumbled mess. Elastomers have glass transition temperatures (T g) 

below room temperature. Glass transition temperature is the temperature below which 

chain motion in the polymer is frozen in. It effectively means that above its T g the 

elastomer is soft and pliable, and below it becomes hard and glassy (Herman, 1996). 

Neoprene, natural rubber, and SBR are referred to as thermoplastic rubbers. But SBS, SIS 

are referred to as rigid thermoplastic elastomers as they are block copolymers. This 

means both ends to a rigid material such as styrene chemically bond the elastomer 

segment, which is hard at room temperature. Elastomers provide greater high temperature 

resistance to pavement deformation. 



34 

A network formed by the polymer with the bitumen achieves improved binder properties. 

This network is composed of flexible branches linked together by thermo-reversible 

bonds. The primary factors affecting the formation of a polymer network, and to give the 

improvement in binder performance are (Brule, 1995; Morgan & Mulder, 1995; Exxon, 

1996): 

• Bitumen composition, in particular asphaltene content. 

• Compatibility between the bitumen oils and resins fractions and the flexible polymer 

branches. 

The choice of polymer to use depends on the environmental conditions, topography, and 

traffic loading the road surface is subject to. Exxon ( 1996) state that plastomeric 

polymers have been found to be compatible with paraffinic, naphthenic and some 

aromatic bitumen, while elastomeric polymers have been found to be compatible with 

aromatic bitumen. But, the reasons why this is so are not documented. 

2.12 Interactions During Manufacture 

When the polymer is added to hot bitumen, the maltene components immediately start to 

penetrate into the polymer particles, causing (in the instance of SBS polymer) the styrene 

and butadiene domains of the polymer to become solvated and swollen (Mulder & 

Morgan, 1995). The physical form of the polymer at this stage is important, as the 

dissolution of it is largely dependent on its surface area. The greater the surface area, the 

faster the dissolution process will proceed. Dissolution is easy to achieve with finely 

divided polymer forms such as powder in a low shear mixer. If the polymer is in the form 

of 3 mm pellets, it is necessary to reduce the particle size as quickly as possible, this can 

be achieved by using a high shear disintegrator. 

The uptake of the maltenes by the polymer generally amounts to 6 to 9 times the mass of 

the polymer (polymer rich phase). Blends of bitumen and polymer are not necessarily 

always homogeneous and single phase, and on cooling a two-phase system can become 

apparent. The second phase is made up of asphaltenes and the balance of the maltenes 

(Mulder & Morgan, 1995; Rozeveld, et al., 1997). 



The key parameters influencing the mixing process include: 

grade of polymer, 

physical form of polymer, 

nature and grade of bitumen, 

type of equipment (low shear or high shear). 

2.12.1 Grade of polymer 

35 

The molecular weight of the polymers is an important consideration, as very high values 

will generally cause more viscous and unworkable blends. For SBS there are linear and 

radial polymer types, with the radial having a much higher molecular weight and is more 

difficult to process. 

2.12.2 Physical form of polymer 

Polymers can be in powdered, pellet, or liquid form depending on the polymer type and 

grade. Powdered and liquid forms are easy to disperse with low shear equipment. But 

pellets require physical size reduction (Exxon, 1996). 

2.12.3 Nature and grade of bitumen 

A high maltenes content and high aromatics content in bitumen will facilitate swelling of 

the polymer to a greater extent than those with high asphaltene content. This is viewed as 

beneficial for low shear mixing with powdered polymers (Mulder & Morgan, 1995). Low 

viscosity bitumen aids pre-dispersion of the polymer in the bitumen and speeds the 

penetration and swelling of the polymer particles. The temperature of the bitumen is 

usually l 70°C-l 90°C when adding the polymer, any higher can lead to viscosity 

increases and degradation of the polymer. 

2.12.4 Mixing equipment 

Low shear - facilitates swelling and dissolving of the polymer by the bitumen. 

High shear - physically reduces the polymer particles, leads to faster dispersion and 

solution. 

Higgins Contractors has only low shear blending equipment so the range of polymers 

available is restricted to powdered, or easily dispersed pellet forms, or latex's. 



2.13 Elastomeric Polymers 

2.13.1 Styrene Butadiene Styrene (SBS) 

Structure: Tri-block copolymer. 

- SSSSSSSSSS - BBBBBBBB - SSSSSSS -

styrene butadiene styrene 

HH HH HH HH 
I I I I I I I I 

- -- C - C - ---- --C - C = C - C - ----- ---C - C ---

1 I I I I I 
~~ H H H cc~ 

X y 

36 

z 

An amorphous thermoplastic, it has an atactic structure as butadiene lacks the ability to 

crystallise. The copolymer is produced by a sequential operation of successive 

polymerisation of styrene and butadiene (Brydson, 1989). 

The glass transition temperature (T g) of styrene = l 00°C, and for butadiene = -90°C. 

Tg of copolymer= -55°C. 

The polymer is available in powdered form for low-shear blending equipment. 

There are two key types used for bitumen modification - linear, and radial. 

LinearSBS: 

I 
Polystyrene 

Its number molecular weight (Mn) is approximately 104,000 (A dimensionless quantity) 

Styrene content typically 29% 

Butadiene content typically 71 % 

Radial SBS: ._I __ _. 

Polystyrene 

Molecular weight approximately 204,000 

Styrene content typically 30% 

Butadiene content typically 70% 



37 

SBS obtains its strength and elasticity from a physical rather than chemical cross-linking 

of the molecules into a 3-dimensional network. The physical cross-links result from the 

inherent incompatibility between mid-blocks and the styrene end blocks. The different 

blocks tend to separate into discrete phases, but are chemically linked. Polystyrene end 

blocks impart strength, and the butadiene mid-blocks provide elasticity (Morgan & 

Mulder, 1995). 

The main differences between linear and radial SBS is that radial grades have a much 

higher molecular weight and subsequently are much more viscous. This makes them 

more difficult to incorporate into the bitumen and maintain an acceptable stability; also 

they can be too viscous to effectively emulsify the bitumen. 

SBS improves: 

• Ductility of pavements (more flexible and crack resistant at low temperature) 

• Elasticity of the binder at high temperatures, reduced rutting 

• Aggregate retention 

• Binder softening point to reduce flushing 

Network effects of SBS 

On addition of SBS to bitumen, oily maltenes are absorbed by the polymer, which results 

in swelling and extension of the polymer, which swells to 6 - 9 times its initial volume. In 

a 2-phase system this is referred to as the polymer rich phase, and if this phase is 

sufficiently extended will become macroscopically continuous throughout the total blend. 

This happens at about 3 - 8% concentration of the polymer into the bitumen. Formation 

of the continuous network is usually evidenced by the S-shaped softening point vs 

polymer concentration curve (Morgan & Mulder, 1995). 

Elastic networks form upon cooling i.e. <70°C if sufficient polymer is available, usually 
r,. ~ . t ,., • 

at over 3%, and that the bitumen is compatible. Then the styrene blocks tend to associate ,, 

into domains throughout the bitumen and link together. 



2.13.2 Styrene Butadiene Rubber (SBR) 

Structure: Linear random copolymer 

---SSBBSBBSBSSSBBSBBB---

H H H H H H 
I I I I I I 

- --- C - C -- ----- -- C -C = C - C -
I I I I 

H H y 

Polystyrene Polybutadiene 

38 

SBR has an amorphous structure; it lacks the ability to crystallise, as the chain mobility is 

not limited. 

Glass Transition temperature (Tg) = - 45°C. 

Manufactured by emulsion polymerisation (latex) so is available m an aqueous form 

(Feldman & Barbalata, 1996). 

SBR is a high molecular weight copolymer, approximately 175,000. 

Typical styrene content 24% 

Typical butadiene content 76% 

SBR improves: 

• Ductility of pavements (more flexible and low temperature crack resistant) 

• Elasticity of the binder at high temperatures, reduced permanent deformation 

• Aggregate retention 

• Binder softening point to reduce flushing 

SBR network effects 

At a concentration of 1 %, SBR acts like a dispersed polymer. The concentration is small 

enough that it does not significantly affect the rheological properties. At 2% to 3% SBR 

begins to form a localised network structure (Lee et al., 1997). At contents greater than 

3% the local networks begin to interact forming a continuous network throughout the 

bitumen. This network acts as a support structure for the bitumen, resisting deformation. 

The modified bitumen viscosity increases at higher polymer contents due to the 

increasing density of the global network. 



2.13.3 Neoprene (Polychloroprene) 

Structure: Polymer 

-CH2 H 
I I 
C =C- CH2-
I 
CI 

Trans - 1,4 polychloroprene (the most common produced). 

Produced by emulsion polymerisation. 

Molecular weight is approximately 100,000 for fluid grades of the material. 

T8 = - 43°C Tm= 45°C 

It is available in latex form for low-shear blending. Neoprene is the common name used 

and in bitumen the polymer improves: 

• Aggregate retention 

• Resistance to cracking 

• Permanent deformation 

At usual ambient temperature the rubber exhibits a measure of crystallinity. Hence, both 

the raw and cured polychloroprene have higher tensile strength due to stress-induced 

crystallisation (Feldman & Barbalata, 1996). 

The polymer has excellent resistance to solvents, weathering and oxidation, and to ozone 

attack compared to natural rubber. But has poor low temperature properties due to 

crystallisation. The density of polychloroprene is high (1230 kgm-3
) and this can increase 

the price of the elastomer on a volume basis (Feldman & Barbalata, 1996). 

2.13.4 Natural Rubber (Polyisoprene) 

Natural rubber is a diene polymer, meaning that it has a carbon-carbon backbone. 

--{CH2 '\. / CH2 }-

C = C 

/ " H3C H cis - 1,4 Polyisoprene 



40 

The polymer can be harvested from the sap of the Hevea Tree or synthesised by Ziegla­

Natta polymerisation. Natural rubber is highly amorphous, with a molecular weight of 

200,000 to 500,000. It's T8 is around -70°C, so it has good low temperature properties 

(Brydson, 1989). 

The polymer has high elastic properties so it can resist stone loss in road surfacing. But, it 

imparts small stiffness properties compared to SBS, SBR or plastomer polymers. The 

high molecular weight of natural rubber gives rise to very high viscosity when added to 

hot bitumen and should not exceed about 1 % (Whiteoak, 1990; Transit, 1993). 

2.14 Plastomeric Polymers 

2.14.1 Ethylene Methyl Acrylate (EMA) 

Copolymer containing up to 20% acrylic co-monomer. 

Structure: 

H H H H 
I I I I 

--- -- C - C -- ---- -- C - C ------
1 I I I 
H H x H COOR y 

Prepared by free radical, high-pressure polymerisation technique. 

Ethylene is crystalline but the copolymerisation processes will likely cause irregularity of 

the overall molecule, so EMA is probably semi-crystalline. EMA has better thermal and 

abrasion resistance than ethylene vinyl acetate but lower toughness (Feldman & 

Barbalata, 1996). It improves bitumen performance at low and high temperatures due to 

its stiffness, but provides less improvement at higher temperatures than for SBS/SBR 

except in asphalt where it has good rut resistance. The copolymer causes a linear increase 

in softening point as there is no network structure as in the elastomeric polymers, and 

gives a higher viscosity than for SBS at the same percentage content (PIARC, 1999). 



2.14.2 Ethylene vinyl acetate (EV A) 

Structure: A random copolymer. 

H H 
I I 

H H 
I I 

--- -- C - C ---- ---- -- C - C ---------- ---

1 I I I 
H H x H OCOCH3 y 

Ethylene Vinyl Acetate 

41 

Vinyl acetate content varies between 5-50% and controls crystallinity and the flexibility 

of the material (Feldman & Barbalata, 1996). The polymer has both crystalline and 

amorphous characteristics. 

Molecular weight 

Standard practice for EV A' s is to measure melt flow index (MFI) in g/10 minutes, a 

viscosity test that is inversely related to molecular weight. The higher the melt, the lower 

the molecular weight (Morgan & Mulder, 1995). 

Vinyl acetate content 

Regular polyethylene segments pack together (crystalline region) and the bulky vinyl 

acetate groups disrupt this arrangement to give amorphous rubbery regions. The more 

viny I acetate the more rubbery regions and less stiffness of the material. 

There are a range EV A' s based on MFI and vinyl acetate content, for example: An EVA 

with a MFI of 150 and VA of 19% is a 150/19 grade. 

Exxon Chemicals have EVA grades as follows under the Polybilt brand (Exxon, 1996): 

Type 

MFINA: 

101 

2020/ 14 

102 

150/19 

103 

45/33 

106 

1.8/24 

EV A copolymers are generally more easily dispersed in and have relatively good 

compatibility with bitumen, particularly the lower molecular weight types such as 

Exxon's Polibilt 101. It also tends to improve bitumen mix workability because of its 

susceptibility to shear (Exxon, 1996). EV A provides stress cracking resistance, and low 

temperature flexibility. But provides very good rut resistance in asphalt. But is not often 



4L 

used in spray seals but has been used in Microsurfacing and Hot Mix Asphalt. It also 

gives a linear increase in bitumen softening point, as there is no network structure 

present. Hence, the softening point achieved is less than that for elastomers but will 

depend on EV A grade and concentration. 

2.15 Bitumen/Polymer Compatibility 

Bitumen/polymer compatibility is a key aspect that has caused manufacturers problems 

since the blends were first produced. There have been several attempts to describe the 

compatibility of particular bitumen for polymer modification. But the issue is very 

complex and is dependent upon many variables (Morgan & Mulder, 1995; Bearsley, 

1999): 

• Composition of the bitumen 

• Average molecular weight of the individual bitumen fraction 

• Type of polymer 

• Average molecular weight of the polymer 

• Structure of the polymer 

• Polymer content of the final blend 

• Blending temperature and duration 

• Shear experienced during blending 

The successful manufacture of polymer modified bitumen is dependent upon the 

chemistry of the two phases as well as the resulting morphology. The morphology can be 

controlled through a combination of chemistry, initial polymer physical form, and 

blending parameters. Definitions of compatibility vary but generally can mean (Bearsley, 

1999): 

• The polymer is easy to disperse in the bitumen 

• The blended polymer modified bitumen has the desirable mechanical properties 

• The blended polymer modified bitumen keeps these desirable properties after ageing 

• The blended polymer modified bitumen does not undergo phase separation if stored at 

high temperatures 



Brule (1995) states that three results are obtained when bitumen and a given 

thermoplastic polymer are mixed hot: 

1. The rrux 1s heterogeneous: the polymer and bitumen are incompatible. The 

components separate and the mix has poor characteristics. 

2. The mix is totally homogeneous, including at the molecular level. The oils in the 

bitumen solvate the polymer perfectly and destroy any inter-macromolecular 

interactions. The resulting binder is extremely stable, but only very slight 

modification compared to the base bitumen is achieved. Only its viscosity increases. 

;- 3. The mix is m~_co-heterogeneous, and is comprised of two distinct finely interlocked 

phases. This is the desired result, as the compatible polymer "swells" by absorbing 

some of the oily fractions of the bitumen to form a polymer phase distinct from the 

residual bitumen phase. 

Bitumen can be characterised by its colloidal instability index (Serfass et al. , 1992). This 

is defined as the ratio of dispersed phase/dispersing phase as follows : 

Ic=A + S 
R + Ar 

A = Asphaltenes 

R = Resins 

Ar= Aromatics 

S = Saturates 

(3) 

The Colloidal Instability index is actually the inverse of the Colloidal Index ( equation 1, 

pp 15). The Colloidal Instability Index approach has been tested using SBS polymers and 

may not be applicable to other polymers. There is no precise borderline between 

"compatible" and "incompatible" bitumen. Bitumen with an le higher than 0.25 are 

definitely incompatible, those with an le of less than 0.15 are generally compatible 

(Serfass et al., 1992). The le of the Safaniya (Saudi Arabian) bitumen that New Zealand 

uses is 0.80 which suggests that it is very incompatible for modification with SBS and 

may require stabilising with additives. Incompatibility with Safaniya bitumen has been 

noted by Transit, (1993). Chemical cross-linking of the polymer and bitumen can 



44 

effectively force the two materials to be compatible by a stabilisation mechanism The 

use of sulphur (Lesueur et al., 1998), peroxides (PIARC, 1999) and maliec anhydride 

(Engel et al., 1991) has been successful in this respect. 

The introduction of any polymer with a high molecular weight disturbs the dynamic 

equilibrium and reduces the homogeneity of the bitumen system (Lu et al., 1999). The 

polymer competes for the light fractions of the bitumen, resulting in association of 

asphaltene micelles which often leads to phase separation of the PMB blends. Lu et al. 

(1999) conclude that for Styrene Butadiene Styrene (SBS), bitumen with a higher 

aromatic content of 60% to 65% exhibit lower phase separation. An increase in . 

asphaltenes can also increase the phase separation of the PMB blends. The aromatic 

content of New Zealand's bitumen is only 11.2% which suggests that the addition of 

polymer (particularly SBS) will result in phase separation due to the decreased solvating 

power of the aromatics and resins content available. 

2.16 Microscopic Investigations of Bitumen/Polymer Blends 

Microscopic observation techniques can be used to assess the dispersion of the polymer 

phase in t.he bitumen or emulsion and to characterise the microstructural interactions. 

/ Flu(orescence microscopy is the most frequently used technique for assessing the state of 

dispersion of the polymer and bitumen phases (PIARC, 1999). It is based on the principle 

that the polymers, swollen by some of the constituents of the bitumen to which they have 

been added, fluoresce in ultraviolet light. They emit yellow-orange light while the 

bitumen phase remains black: The method uses mercury or xenon arc lamps to provide 

the light source. 

But, while acceptable images are obtained using fluorescence microscopy, the level of 

resolution is not as good to that produced if a laser is used as the light source, such as in 

confocal laser scanning microscopy (CLSM) (Rost, 1992; PIARC, 1999). Both 

fluorescence and reflection methods can be used with CLSM and the technique requires 

no special sample preparation (Rozeveld et al., 1997). The CLSM technique has been 

used by several studies to assess the polymer distribution, network formation and 

compatibility for polymer modified bitumen (Lee et al. , 1997; Rozeveld et al., 1997; 

PIARC, 1999) but not emulsion binder residue or cold mix surfacing. 



45 

When the microstructure 1s very fine, less than one rrucron, the use of electron 

microscopy becomes necessary. Scanning electron microscopy (SEM), and 

environmental scanning microscopy (ESEM) are two methods, but they require 

preliminary treatment of the sample to remove oily fractions that can create artefacts in 

the images (Rozeveld et al., 1997; Michon et al., 1998). An additional technique is that of 

Atomic force microscopy which enables the study of bitumen and polymer modified 

bitumen binder network structures (Loeber et al., 1996; Loeber et al., 1998). The 

technique can resolve particles of less than one micron like the ESEM and SEM 

techniques. 

Microscopy techniques have often been used to characterise the microstructure . 

interactions between bitumen and polymers for modified binders and for asphalt concrete 

(Piazza et al. , 1981; Loeber et al., 1996; Rozeveld et al., 1997; Michon et al., 1998). But 

there has been little publication regarding the microstructure and curing aspects of 

polymer modified bitumen emulsion binders for cold mix applications using any 

microscopy method. Normally physical testing methods are employed to characterise the 

degree of modification of the binder, but direct observations can help improve the 

understanding of the interaction between the emulsified bitumen-polymer after curing by 

water evaporation and the addition of aggregate. 

2.17 Polymer Modified Emulsions 

Polymer Modified Bitumen (PMB) while having considerable in-service performance 

advantages over unmodified or cutback bitumen, does have its own shortcomings as 

follows: 

• Application period is usually quite short and needs to be strictly enforced. The road 

surface prior to spraying must b