Date of Award

Summer 8-2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Abstract

Every year around 400 million tons of asphalt mix is being laid in the United States and a significant portion of it is required for pavement rehabilitation. Cracking is one of the most common pavement distresses that is still not fully understood by the researchers. Very few states mandate tests for cracking resistance during the mix design phase; in addition, the test methods vary a lot from state to state. In the presence of oxygen, the asphalt binder over time undergoes chemical changes and becomes stiff which is known as oxidative aging that makes asphalt pavement more susceptible to cracking. Therefore, proper characterization of asphalt aging is a prerequisite to study the cracking mechanism of asphalt mix. In this dissertation, efforts are given for characterization of oxidative aging, investigation of the effect of aged binder on cracking susceptibility, and development of an antioxidant to reduce the aging-induced cracking.

In this study, rheological characterization of laboratory aged binder and extracted binder from asphalt mix was performed using dynamic shear modulus of the binder to understand oxidative aging. Then the correlation between laboratory binder aging and binder aging in asphalt mix was established and a Rolling Thin Film Oven (RTFO) aging test protocol for warm mix asphalt (WMA) was developed. Another factor for cracking susceptibility of asphalt pavement is the excessive content of reclaimed asphalt pavement (RAP). RAP is added to the hot mix asphalt (HMA) for economic and environmental interest but the highly aged binder in RAP makes the mix stiffer and escalates the cracking. Because it is quick and simple, the viability of using a handheld Fourier Transformed Infrared (FT-IR) spectrometer was investigated to detect and quantify the aging of binder by measuring the absorbance intensity of carbonyl groups. An in-situ test method was developed to determine the reclaimed asphalt pavement (RAP) content in the plant mix using a handheld FT-IRS.

The use of rejuvenators is the most suitable strategy to accommodate a higher amount of RAP in HMA and bio-based rejuvenators are of high interest. In this study, four types of cracking tests were performed on asphalt mix made with two different categories of rejuvenators: petroleum-based and bio-based oil. It was concluded that petroleum-based aromatic oil performed better to restore the cracking potential of the mix with high RAP content. Sound understanding of the cracking mechanism is necessary to find the right cracking susceptibility test for asphalt mix and design a cracking resistant mix. A finite element model of semi-circular bend (SCB) test of asphalt mix incorporating the cohesive zone material (CZM) model was performed using ANSYS to simulate and predict the fracture potential of asphalt mix as conducted in the laboratory according to ASTM D 8044 test method. The CZM properties of fine aggregate mastic (FAM) needed for ANSYS model of SCB test was determined by a laboratory double cantilever beam test and corresponding finite element model of double cantilever beam test., It was concluded that critical energy release rate (Jc) of asphalt mixture predicted from ANSYS model of SCB test was precise when compared with the laboratory SCB test of asphalt mix.

Finally, locally sourced Lignin was used as an asphalt performance enhancer as well as an antioxidant. It was observed that lignin could improve the high-temperature performance grade of the binder and reduce the aging index. Mix made of lignin modified binder showed better cracking resistance by improving the flexibility index.

Through this study, understanding oxidative aging helped with developing a revised short-term aging protocol for warm mix asphalt. One of the immediately implementable outcomes of this research is the in-situ application of handheld FT-IR spectrometer for quality control during the mix production at the plant through determining the reclaimed asphalt pavement content. This research will contribute to choosing suitable rejuvenators by understanding the cracking mechanism of asphalt mix through different tests. The finite element cohesive zone material model developed in this study can precisely predict fracture resistance of the mix in semicircular bending test by performing a double cantilever beam test of fine aggregate mastic. Viability of using bio based rejuvenator for RAP mixes and also the suitability of utilizing locally sourced lignin as an oxidant in asphalt binder were addressed in this research and the findings will help implement these environmentally friendly alternatives in resolving cracking related problems in asphalt pavements.

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