Rheological properties, moisture susceptibility and chemical functioning of soybean oil-based modified asphalt binders
Abstract
Petrochemical asphalt binder modifiers are used to enhance performance properties of flexible pavements. National transportation agencies have expressed interest in asphalt binder modifiers from renewable resources. Acidulated soybean soapstock with its surfactant qualities and soybean vulcanized vegetable oil (VVO) with its elastic properties are two possible soybean oil-based modifiers that may improve asphalt binder performance. Research with vegetable oil-based asphalt binder modifiers has shown chemical changes which affect high and low temperature properties in addition to moisture susceptibility. The purpose of this examination is first to demonstrate the high and low rheological properties and moisture susceptibility of these asphalt binder soybean oil-based modifier blends. Since modifying asphalt binder will alter its chemical functionality, the second aim of this study is to verify the chemical mechanism(s) of asphalt binder modification. High temperature testing demonstrates that soybean VVO produces harmful sulfur emissions at high temperatures and does not behave as an elastomer in asphalt binder contrary to expectations. Additional high temperature testing indicates that asphalt binders modified with acidulated soybean soapstock show a reduction in softening point, viscosity and complex modulus, as well as an increase in phase angle. However, low temperature results of binder modification are source specific with no clear trend in stiffness or flexural creep flow rate. Asphalt binders modified with 1 percent acidulated soybean soapstock generally perform better than unmodified asphalt binders or asphalt binders with a 3 percent modification level. Results from moisture susceptibility testing suggest that asphalt binders modified with 1 percent acidulated soybean soapstock perform as well or better than unmodified asphalt binders. Regarding chemical functionality, evidence suggests that the soy fatty acids in acidulated soybean soapstock may have two functions. One function is to act as a low molecular weight solvent and the second is to act as molecular lubrication. Additionally, results suggest that moisture resistant divalent bonding may be facilitated by the adding 1 percent acidulated soybean soapstock. It is the recommendation of this investigation that binders modified with 1 percent acidulated soybean soapstock be considered for engineering applications using polymer modified binders and 3 percent acidulated soybean soapstock for recycled asphalt pavements.
Degree
Ph.D.
Advisors
Haddock, Purdue University.
Subject Area
Civil engineering
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