Polymer Modified Bitumen
DESCRIPTION OF POLYMER MODIFIED BITUMEN (PMB)
Polymer Modified Bitumen (PMB) is bitumen (asphalt) combined with one or more polymer materials. This modification is done with the aim of enhancing the mechanical properties of the bitumen material. Polymer Modified Bitumen (PMB) is typically used on road pavements, particularly those that are intended to withstand heavy-duty traffic and extreme weather conditions. This material is also used as a sealant in residential roofing applications. Polymer-modified bitumen (PMB) is typically made by combining bitumen with a styrene-butadiene-styrene (SBS) copolymer. The addition of the polymer makes the bitumen more elastomeric in nature. Some of the desirable properties of Polymer Modified Bitumen (PMB) include improved strength, cohesiveness, and resistance to fatigue and deformation. Polymer Modified Bitumen (PMB) also possesses less temperature sensitivity than plain bitumen. This is particularly crucial for pavement applications because the material will not flow or become soft in high temperatures while it maintains its workability and flexibility in colder temperatures. Of particular importance to corrosion, the industry is PMB’s enhanced waterproofing properties. When applied to steel pipes, PMB prevents water or other electrolyte-rich fluids from coming into contact with the metal substrate. This property makes PMB coatings ideal for barrier protection in aggressive environments.
POLYMER MODIFED BITUMEN (PMB)
Bitumen has been used as a construction material for centuries and continues to be a valued engineering material for many modern applications. Over the years, numerous studies have been performed with the aim of improving bitumen’s performance in the field. One of the enhancements that have produced desirable results is the addition of polymer to bitumen. Polymers serve to improve bitumen’s elasticity, thus providing numerous benefits when used in Bitumen-based applications. Styrene-butadiene styrene (SBS), which acts as a binder modification agent, is known to increase the longevity of pavements that are subjected to a range of onerous loading on a daily basis, including high traffic loading and high thermal stresses.
OTHER BENEFITS OF PMB WHEN IN PAVEMENT APPLICATIONS INCLUDE:
- Enhanced rigidity
- Improved resistance to deformation
- Improved resistance to cracks and stripping
- Increased durability
- Enhanced water resistance
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 (PMB), 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. aging and softening points. 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. 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. Polymer Modified Bitumen (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. 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.
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:
- Higher rigidity
- Increased resistance to deformation
- Increased resistance to cracks and stripping
- Better water resistance properties
- High durability
COST BENEFITS OF USING PMB
Some studies show that polymer-modified bitumen can possibly result in potential cost savings when used in some applications. The enhancement in mechanical properties allows PMBs to be applied in thinner layers than unmodified bitumen without exhibiting a reduction in performance. Improvements in binder strength, flexibility and toughness significantly improve the asphalt’s fatigue resistance, even in hard binders. The Road Research Laboratory of the Delft University of Technology in the Netherlands conducted a study comparing modified and unmodified bitumen using a finite element model (FEM) analysis. The study ultimately determined that thickness reductions of up to 40% can be realized when using modified bitumen. The FEM model also showed that even with reduced thicknesses, the damage expected in the polymer-modified bitumen was significantly lower than in unmodified bitumen when subjected to the same types of loading conditions.
ADVANTAGES OF USING PMB
- Stronger road with increased marshall stability value and greater Rigidity.
- Better resistance towards rainwater and water stagnation.
- No stripping and no potholes.
- Better resistance to permanent deformation
- Reduction in pores in aggregate and hence less rutting and raveling.
- Much higher durability
COMMON TYPES OF PMB
The following table lists some common asphalt cement and HMA modifiers and their general purpose/use.
| TYPE | GENERAL PERPOSE TO USE | GENERIC EXAMPLES |
|---|---|---|
| Filler | Fill voids and therefore reduce optimum asphalt content Meet aggregate gradation specifications Increase stability Improve the asphalt cement-aggregate bond | Mineral filler crusher fines lime Portland cement fly ash Carbon black |
| 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 Lignin |
| 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) | Natural Latex Synthetic latex (e.g., Polychloroprene latex) Block copolymer (e.g., Styrene-butadiene-styrene (SBS)) Reclaimed rubber (e.g., crumb rubber from old tires |
| Plastic | Polyethylene/polypropylene Ethylene acrylate copolymer Ethyl-vinyl-acetate (EVA) Polyvinyl chloride (PVC) Ethylene propylene or EPDM Polyolefin |
|
| 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 | Natural: Asbestos Rock wool Manufactured: Polypropylene Polyester Fiberglass Mineral Cellulose |
| Oxidant | Increase HMA stiffness after the HMA is placed | Manganese salts |
| Antioxidant | Increase the durability of HMA mixtures by retarding their oxidation | Lead compounds Carbon Calcium salts |
| Hydrocarbon | Restore aged asphalt cement to current specifications Increase HMA stiffness in genera | Recycling and rejuvenating oils Hard and natural asphalts |
| Antistripping Agents | Minimize stripping of asphalt cement from aggregates | Amines Lime |
| Waste Materials | Replace aggregate or asphalt volume with a cheaper waste product | Roofing shingles Recycled Tires Glass |
USE AS NEEDED
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 RHEOLOGICAL PROPERTIES OF CONVENTIONAL BINDERS MAY BE MODIFIED BY THE INTRODUCTION OF:
- Elastomers;
- Plastomers;
- Crumb rubber;
THE MODIFICATION IS COSTLY AND IS NORMALLY JJUSTIFED WHEN BITUMINOUS SURFACING ARE SUBJECTED TO SERVERE CONDITIONS SUCH AS:
- Steep gradients;
- Very high road surface temperature;
- High traffic loading; or
- Heavily trafficked intersections.
Modification may also be advantageous for surfacing on highly flexible and cracked pavements, where an improvement in the rheological properties of the bitumen is required. Use in such applications should be guided by expert opinion.
IN ADDITION TO THE PRIMARY AIMS ABOVE, THE RANGE OF PROPERTIES IMPROVED INCLUDE :
- Durability;
- Aggregate retention;
- Resistance to permanent deformation;
- Resistance to fatigue cracking;
- Cohesion (internal strength);
- Elasticity;
- Viscosity is less susceptible to temperature changes.
- Modification agents
The primary aim of the modification of bitumen for use in structural layers is to increase the resistance of these layers to permanent deformation at high road temperatures without compromising the properties of these layers over the rest of the prevailing temperature range. The use of polymer-modified bitumen to obtain improved performance is rising as a result of increases in tire pressures, axle loads, and higher traffic volumes.
IMPROVED PERFORMACE CAN BE ACHIEVED IN TWO WAYS, BOTH OF WHICH ARE AIMED AT REDUCING THE PERMANENT STRAIN:
- An increase in the elastic component with an associated reduction in the viscous component;
- Stiffening of the bitumen to reduce the total viscoelastic response of the layer.
The modification is achieved by the introduction of polymers (including crumb rubber), aliphatic synthetic wax, or naturally occurring hydrocarbons. Polymer-modified bitumen (PMB) 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.
TECHNICAL DATA SHEET OF POLYMER MODIFIED BITUMEN
| S.NO | Designation | PMB 120 | PMB 70 | PMB 40 | Test Method |
|---|---|---|---|---|---|
| 1 | Penetration at 25 ֯C, 1/10mm, 100g, 5 sec | 90-150 | 50-90 | 30-50 | ASTM D5 |
| 2 | Softening Point, (R&B), ֯C, Min | 50 | 55 | 60 | ASTM D36 |
| 3 | Elastic Recovery at 15 ֯C ,%, Min | 60 | 60 | 60 | ASTM D6084 |
| 4 | Flash point , COC, ֯C , Min | 220 | 220 | 220 | ASTM D92 |
| 5 | Separation, Difference in Softening Point,(R&B), ֯C, Max | 3 | 3 | 3 | – |
| Thin Film Oven Test & Test on Residue | |||||
| 7a | Loss in Mass, %, Max | 1.0 | 1.0 | 1.0 | ASTM D1754 |
| 7b | Reduction in Penetration of residue at 25 ֯C , 100g, 5s, %,Max | 35 | 35 | 35 | ASTM D5 |
| 7c | Increase in Softening Point, ֯C, Max | 7 | 6 | 5 | ASTM D36 |
| 7d | Elastic Recovery at 25 ֯C, %, Min | 50 | 50 | 50 | ASTM D6085 |
