What are the Types of Modifier in Bitumen?

By Nurul Hidayah

INTRODUCTION
Bitumen is a black or dark brown non-crystalline solid or viscous material, composed principally of high molecular weight hydrocarbons, having adhesive properties, derived from petroleum either by natural or refinery processes and substantially soluble in carbon disulphide. Refer to Ali Akhber Yousefi (2002), bitumen in pure form is not suitable for modern roads and present traffic, therefore forced engineers to modify bitumen to improve its performance during service life.

The modified binder are more stable under heavy loads, braking and accelerating forces and shows increased resistance to permanent deformation in hot weather. It resists fatigue loads and having better adhesion between aggregates and binders.

TYPE OF BITUMEN MODIFIER AND ADDITIVE

There are 3 type of bitumen modifier, namely :
(1) physical modification
(2) chemical modification
(3) other type modification

The table 1 below showed the type of modifier and example of additive that being used to modify the bitumen.

Table 1: The type of physical modifier and additive used in the material (Read and Whiteoak, 2003)

TYPE OF MODIFIER	TYPE OF ADDITIVE
(1) Thermoplastic Elastomers	Styrene – butadiene – styrene (SBS) Styrene – butadiene – rubber (SBR) Styrene – isoprene – styrene (SIS) Styrene – ethylene – butadiene – styrene (SEBS) Ethylene – propylene – diene terpolymer (EPDM) Isobutene – isoprene copolymer (IIR) Natural rubber Crumb tyre rubber Polybutadine (PBD) Polyisoprene
(2) Thermoplastic Polymer	Ethylene vinyl acetate (EVA) Ethylene methyl acrylate (EMA) Ethylene butyl acrylate (EBA) Atactic polypropylene (APP) Polyethylene (PE) Polypropylene (PP) Polyvinyl Chloride (PVC) Polystyrene (PS)
(3) Thermosetting Polymers	Epoxy Resin Polyurethane Resin Acrylic Resin Phenolic resin

Among many different polymers used in bitumen modification such as thermoplastics, thermosets, thermoplastic elastomers, the rubbers seems to be more attractive. Although thermoplastic elastomers such as styrene-butadiene-styrene triblock copolymer (SBS) or its hydrogenated forms and plastomers such as ethylene-vinylacetate copolymer (EVA) are good bitumen modifiers, rubbers are preferred due to their lower prices. In fact, bitumen is supposed to keep its physical and rheological properties constant at different service temperatures and loading conditions and transforms itself to a low viscosity Newtonian fluid at mixing temperature (165ºC). This type of bitumen is called “ideal bitumen”. Constant rheological properties in a wide range of temperatures correspond to rubbery behaviour. It is concluded that the rubbers should be able to modify bitumen properties very well. Therefore, many types of rubbers were introduced in bitumen (PBR, SBR and its latex, ground tire rubber etc.)

Chemical modification used the additive such as organo- metallic compounds, sulphur and lignin. It used the chemical agent as additive to modify the characteristic of pure bitumen. Due to vary complex structure of bitumen, chemical modification of bitumen have not been commercialized as physical modification. The types of additive used with different types of modifier clearly shown in Table 2.

Table 2: Type of additive adding to chemical modifier (Read and Whiteoak, 2003; Asphalt Academy, 2007)

TYPE OF MODIFIER	TYPE OF ADDITIVE
Chemical Modifiers	Organo-metallic compounds Sulphur Lignin
Fiber	Cellulose Alumino-magnesium silicate Glass fiber Asbestos Polyester Polypropylene
Adhesion improvers	Organic amines Amides
Antioxidants	Amines Phenols Organo-zinc/organo-lead compounds
Natural asphalts	Trinidad Lake Asphalt (TLA) Gilsonite Rock asphalt
Fillers	Carbon black Hydrated lime Lime Fly ash
Extender	Sulphur

CONCLUSION
As conclusion, each modifier has their own additives as modifier agent. There are many modifier materials that can be used to mix with bitumen to improve their performance as paving material. Rubbers are preferred as bitumen modifier due to their lower prices and the availability. Nevertheless, the selection of modifier is depending on the user or company.

REFERENCES
[1] Ali Akhber Yousefi (2002) “Rubber Modified Bitumens.” Iranian Polymer Journal, 11 (5).
[2] Read, J and Whiteoak, D (2003). “Shell Bitumen Handbook.” 5th. Ed. London.
[3] Asphalt Academy (2007) “Technical Guideline: The Use of Modified Binders in Road Construction.” Pretoria. Asphalt Academy.

We at engineeringcivil.com are thankful to Nurul Hidayah for submitting this very useful information on types of modifiers in bitumen.

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