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 3 decades and with it the demand for asphalt that can withstand the challenge. Polymers are often used as additives to make asphalt with better physical properties over a widened temperature range. This modified asphalt leads to pavement and roofing materials that last on average 4-6 years longer.
The Benefits of Modified Asphalt
Increased Rutting Resistance
Outstanding High Temperature Performance
Improved Weather Resistance
Increased Temperature Stability
Outstanding Crack Resistance
There are many different chemical and polymer additives that are in use today 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 that are commonly used to modify asphalt include styrene butadiene and styrene-butadiene-styrene block co-polymers. Common plastomers used as asphalt additives are ethylene vinyl acetate and low density polyethylene. Many different kinds of chemical modifiers are used in asphalt as well. Polyphosphoric acid is traditionally used in combination with polymer modifiers to increase viscosity and stiffness at high temperatures. Hydrocarbons can be added to provide softening or hardening effects and anti-stripping additives are included 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 and pavement Westlake Chemical compared the performance of SBS rubber and EVA to their polyethylene polymer Epolene® EE-2. The polymers were tested on ease of blending, effect on viscosity, aging stability, and impact on SHRP performance. 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 (normally 2-3 hours). To demonstrate this the solution rates of SBS and Epolene® EE-2 were measured by change in softening point overtime.
Solution Rate for Epolene EE-2 and SBS
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 only slightly increased with Epolene® EE-2 as compared to a drastic increase seen with SBS. This allows asphalt blends containing Epolene® EE-2 to have better hot-mix workability and no observable segregation.
Effect of Additive on Blend Viscosity
Aging Stability & Compatibility
The viscosities of asphalt AC-20 blends containing Epolene® EE-2, EVA, and SBS were compared over a 21 day period. Typically asphalt blends are only held in molten storage for 2-3 days prior to hot-mix preparation. However, sometimes weather conditions or mechanical problems can lead to unexpected delays and a much longer storage time is necessary. 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 handling issues that occur due to viscosity increases from aging.
Viscosity of AC-20 Blends
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
Impact on High Temperature SHRP Performance
One of the main benefits of using a modified asphalt blend is the superior performance at high and low temperatures. Epolene® EE-2 was tested in multiple blends and has shown that it increases the high temperature SHRP grade of an asphalt blend without effecting the low temperature SHRP grade. This leads to an overall increase in the useful temperature interval (UTI). The observable increase depends on the amount of Epolene® EE-2 added to the blend and the type of asphalt being modified. SHRP grades for the tested blends are listed below.
Effect on SHRP Performance
In review of the data presented above it is clear to see that Epolene® EE-2 is a superior asphalt additive. It provides the same benefits to asphalt as SBS and EVA but it is also easier to blend, does not effect viscosity, has compatibility with a wide range of asphalt, and offers improved storage stability. Click here to download our asphalt modification brochure and then contact us to request your free sample of Epolene®.