Bitumen has been used for thousands of years and its importance as a valued engineering material continues to increase. The interest in the modification of bitumen using polymers, whether virgin, scrap or polymer blends, is intense. The last two decades, in particular, have seen an increase in the number of academic groups studying polymer-modified bitumen and correspondingly the peer-reviewed literature in the field has increased. Initially, studies on polymer modified bitumen focused more on engineering and empirical measurements, e.g. ageing and softening point. However, in recent years a plethora of techniques have been employed in the study of the effect of the addition of polymers on a range of bitumen properties, polymer_bitumen morphology and polymer_bitumen interactions.
Pavements designed and constructed for heavy-duty traffic and extreme weather conditions require specially designed engineered Bitumen Grades. By changing the characteristics of normal bitumen with the addition of a polymer, either they are of elastomeric nature or elastomeric, we succeed to obtain bitumen that allows the mixture to be more cohesive, with much more strength and significant higher resistance to parameters like fatigue and permanent deformations for road pavements.
Polymer modified bitumen:
(PMB) is one of the specially designed and engineered bitumen grades that are used in making pavement, roads for heavy duty traffic and home roofing solutions to withstand extreme weather conditions. PMB is a normal bitumen with the added polymer, which gives it extra strength, high cohesiveness and resistance to fatigue, stripping and deformations, making it a favorable material for infrastructure.
When a polymer is added to regular bitumen, it becomes more elastomeric, which provides it with additional elasticity. The polymer that is added is styrene butadiene styrene (SBS), which acts as a binder modification agent. The primary objective of SBS polymer modified bitumen is to provide extra life to pavement, roads and construction designs. Some of the qualities exhibited by PMB are:
Advantage of using polymer modified bitumen:
The following table lists some common asphalt cement and HMA modifiers and their general purpose/use.
|type||General Purpose or Use||Generic Examples|
|filler||Fill voids and therefore reduce optimum asphalt content
Meet aggregate gradation specifications
Improve the asphalt cement-aggregate bond
|extender||Substituted for a portion of asphalt cement (typically between 20–35 % by weight of total asphalt binder) to decrease the amount of asphalt cement required||Sulfur
|rubber||Increase HMA stiffness at high service temperatures
Increase HMA elasticity at medium service temperatures to resist fatigue cracking
Decrease HMA stiffness at low temperatures to resist thermal cracking
(see Figure 2)
(e.g., Polychloroprene latex)
(e.g., Styrene-butadiene-styrene (SBS))
(e.g., crumb rubber from old tires)
Ethylene acrylate copolymer
Polyvinyl chloride (PVC)
Ethylene propylene or EPDM
|Rubber-Plastic Combinations||Blends of rubber and plastic|
|Fiber||Improving tensile strength of HMA Mixtures
Improving cohesion of HMA Mixtures
Permit higher asphalt content without the significant increase in the drain down
|Oxidant||Increase HMA stiffness after the HMA is placed||Manganese salts|
|Antioxidant||Increase the durability of HMA mixtures by retarding their oxidation||Lead compounds
|Hydrocarbon||Restore aged asphalt cement to current specifications
Increase HMA stiffness in general
|Recycling and rejuvenating oils
Hard and natural asphalts
|Antistripping Agents||Minimize stripping of asphalt cement from aggregates||Amines
|Waste Materials||Replace aggregate or asphalt volume with a cheaper waste product||Roofing shingles
While the benefits of using modified asphalts are widely acknowledged, not all asphalt mixes or treatments need to be modified. Each application should be evaluated to determine if the traffic loading, anticipated service life, environmental conditions and desired performance justify the use of modifiers. Modified asphalts can be a good investment.
The modification is achieved by the introduction of polymers (including crumb rubber), aliphatic synthetic wax or naturally occurring hydrocarbons.
Polymers can be broadly categorized as “elastomers” (sometimes referred to as thermoplastic elastomers) for improving the strength and elastic properties of a binder, and “plastomers” (sometimes referred to as
thermoplastic polymers) for increasing the viscosity of the bitumen.