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    Polymer-Modified Asphalt Provides Longer Service Life

    There is more stress on pavement today than ever before. Increased traffic volume and trucks carrying heavier loads are the main contributing factors. The demand for better, longer-lasting roads has increased drastically over the past three decades, and with it, the demand for asphalt that can withstand the challenge. 

Polymers are often used as additives to make asphalt mixes with better physical properties over a wide temperature range. This modified asphalt mix leads to pavement and roofing materials that last four to six years longer on average.

The Benefits of Modified Asphalt


 
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    Pavement

    • Improved compaction
    • Increased rutting resistance
    • Outstanding high-temperature performance
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    Roofing

    • Improved weather resistance
    • Increased temperature stability
    • Outstanding crack resistance

Asphalt Additives

Many different chemical and polymer additives are used to improve the performance of asphalt. In general, polymer modifiers are the most common type of asphalt additive. Polymer asphalt modifiers fall into two categories: elastomers and plastomers. Elastomers commonly used to modify asphalt include styrene-butadiene and styrene-butadiene-styrene (SBS) block copolymers. Common plastomers used as asphalt additives are ethylene vinyl acetate (EVA) and low-density polyethylene. 

Many kinds of chemical modifiers are used in asphalt as well. For example, polyphosphoric acid is traditionally used with polymer modifiers to increase viscosity and stiffness at high temperatures. Hydrocarbons can be added to provide softening or hardening effects. Also, antistripping additives are used to improve moisture resistance. Careful consideration should be given when selecting additives to optimize the performance of asphalt.

Selecting The Best Asphalt Additive

In a study to determine which type of additive works best in asphalt for roofing material and pavement applications, Westlake Chemical compared the performance of SBS rubber and EVA to their polyethylene polymer, Epolene® EE-2. These additives were tested for ease of blending, effect on viscosity, and aging stability. The results of the study are outlined below.

Ease of Blending

Unlike SBS and other asphalt modifiers, Epolene® EE-2 does not require high-shear blending or milling processes to be added to asphalt. Epolene® easily melts into molten asphalt, and blending is typically complete in the time it takes to homogenize the mixture, which is normally two to three hours. To demonstrate this, the solution rates of SBS and Epolene® EE-2 were compared by the change in softening point over time. 

 

Solution Rate for Epolene EE-2 and SBS
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Effect on Viscosity

The viscosities of AC-10 asphalt modified with equal amounts of SBS and Epolene® EE-2 were measured. The study found that blend viscosity is slightly increased with Epolene® EE-2 compared to a drastic increase seen with SBS. This allows asphalt mixes containing Epolene® EE-2 to have better hot-mix workability and no observable segregation.

 

Effect of Additive on Blend Viscosity
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The following results show that increasing the concentration of Epolene® EE-2 within AC-5 and AC-20 asphalt mixes does not increase the viscosity of the mix. On the other hand, increasing the concentration of SBS and EVA polymers proportionally increases viscosity. This indicates that better flexibility is gained in optimizing concentrations of Epolene® EE-2 without necessitating a significant change in viscosity. 

Aging Stability & Compatibility

The viscosities of asphalt AC-20 blends containing Epolene® EE-2, EVA, and SBS were compared over a twenty-one-day period. Typically asphalt blends are only held in molten storage for two to three days prior to hot-mix preparation and paving. However, weather conditions or mechanical problems can sometimes lead to unexpected delays, and a much longer storage time is necessary before paving. As shown below, the viscosity of the blend containing Epolene® EE-2 remains much more stable over the testing period. This stability is vital to prevent drastic viscosity changes due to aging and subsequent handling issues.


Viscosity of AC-20 Blends 
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Additionally, the compatibility of Epolene® EE-2 and SBS with many different types of asphalt are compared below.  The ring and ball softening point of top and bottom samples of stored blends were measured as an indicator of polymer separation. The compatibility of Epolene® EE-2 to multiple asphalt types is far superior to SBS.  The use of Epolene® EE-2 leads to blends that are storage stable with no polymer separation.  This allows consumers of modified asphalt more flexibility in regards to storage and use. 


Compatibility Measured by Polymer Separation
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The compatibility of Epolene® EE-2 in multiple asphalt types is far superior to SBS. The use of Epolene® EE-2 leads to blends that are more storage stable with no polymer separation. This allows consumers of modified asphalt more flexibility in storage and use. 

Conclusion

In review of the data presented above, it is clear that Epolene® EE-2 is a superior asphalt additive. It provides similar benefits to asphalt as SBS and EVA; however, it is easier to blend, does not affect viscosity, has compatibility with a wide range of asphalt sources, and offers improved storage stability. This makes Epolene® EE-2 a necessary additive in pavement, roofing, and many other applications that require better asphalt performance and longevity. Click here to download Westlake's asphalt modification brochure. Contact us below to request your free sample of Epolene®.

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