Date of Award

Summer 8-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Materials and Infrastructure Systems

First Advisor

Nazimuddin M. Wasiuddin

Abstract

Styrene-butadiene-styrene (SBS) is the most common modifier used in asphalt binder modification because of its superior performance compared to some others that are used. SBS modified asphalt binder increases the rutting resistance and decreases the fatigue and thermal cracking susceptibility of asphalt pavement. However, SBS modified asphalt binder tends to separate and is subjected to thermal degradation during construction and aging degradation during its service life. As a result, quality control of SBS modified asphalt binder is needed, although no standard test method is available to quantify SBS degradation due to aging.

In this study, two methods for quantifying SBS polymer in asphalt binder were investigated: by mechanical and by chemical analysis. For mechanical analysis, a novel dynamic shear rheometer (DSR)-based extensional deformation test was developed using Sentmanat extensional rheometer (SER). From the second peak elongation force parameter, different polymers can be identified as elastomeric and plastomeric. Finally, the second peak elongation force was proposed as a parameter to quantify elastomeric polymer in asphalt binder with a calibration curve.

For chemical analysis, the Fourier transform infrared (FT-IR) spectrometer with attenuated total reflectance (ATR) was used to collect the absorbance intensity of the SBS modified asphalt binder. No significant effect of the difference in PG binders, the types of SBS polymer, and the presence of crosslinking agent were observed on polybutadiene (PB) and polystyrene (PS) functional groups. Therefore, PB and PS end blocks were analyzed to establish a universal regression model for SBS polymer quantification in asphalt binder. The PS model was found to be the best fit model (R2 = 0.97) for SBS quantification after verifying with refinery supplied SBS modified binders with initially unknown SBS contents.

The extensional deformation test parameters were investigated to determine SBS degradation due to aging during construction and service life. Laboratory aging such as rolling thin film oven (RTFO) and pressure aging vessel (PAV) were performed for SBS modified asphalt binder and mixture. Two parameters (F2 and F2/F1) were proposed to evaluate the SBS degradation directly after oxidative aging. Both values reduced after RTFO aging and further reduced after PAV aging, which indicated SBS polymer degradation.

Finally, the FT-IR spectrometer was used to understand the change in different functional groups of the unmodified and modified asphalt binder after oxidative aging. SBS content in the asphalt binder decreased after RTFO and PAV aging.

Based on the findings of this study, an extensional deformation test was recommended to be used for SBS polymer content determination and aging related SBS degradation. The FT-IR based universal calibration curve developed in this study can predict SBS content in about 30-min using ten samples in the asphalt plant. Therefore, the findings of this study will contribute significantly to the quality control of the asphalt binders.

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