Civil Engineering ETDs

Hasan Faisal

Publication Date

1-30-2013

Abstract

In this study, asphalt binder and asphalt concrete (AC) materials are characterized using laboratory nanoindentation testing and mechanical models. Traditionally, laboratory nanoindentation test data is analyzed using the Oliver-Pharr method to determine elastic modulus and hardness of materials. In a nanoindentation test, a test sample surface is indented or loaded by a hard indenter tip and then unloaded. In the past, several studies of the polymer materials area have selected a loading rate and dwell time (i.e., the peak load is kept constant for a few seconds before unloading) to avoid or minimize the viscous effect of a material. No studies have attempted to examine the effects of dwell time and loading rate on viscous materials such as asphalt binder, which is the main topic of discussion in this study. This study focuses on determination of mechanical properties such as the elastic modulus and the hardness of viscoelastic materials, like asphalt, from nanoindentation load-displacement data. An existing spring-dashpot-rigid (SDR) element model developed by Oyen and Cook is employed as well as the well-established Oliver Pharr method. The SDR model uses the loading, holding and unloading time-displacement data to predict the modulus, hardness and viscosity of the material. The model has shown excellent agreement with the laboratory indentation data of asphalt binder. Further, the SDR model is calibrated for nanoindentation test data of polymer modified asphalt binder. In addition, mechanical models such as the Voigt model and the Burger model are fitted to creep displacement and time data from nanoindentation tests to predict viscosity, retardation time and creep compliance for asphalt binder. All the models are found to fit very well with an average R2-value of 0.99 for the Voigt model and R2-value of 0.99 for the Burger model. Lastly, the nanoindentation test is performed on an AC (solid) sample to understand the aging in AC. Nanoindentation is done on two different parts of the AC sample: one on the mastic part (mix of asphalt binder and fines) and the other on the pure aggregate part. One hundred indentations were made in a single test on the mastic part to capture the heterogeneity. Approximately sixty indentations were made during a single indentation test on the aggregate part of AC. A small dwell time was applied to reduce the viscous effect of the mastic.

Keywords

Asphalt concrete--Testing, Binders (Materials)--Testing, Nanotechnology.

Sponsors

This research is funded by the National Science Foundation (NSF) through GOALI program. NSF grant number is 0900778 and the program is Structural Materials & Mechanics (SMM).

Document Type

Thesis

Language

English

Degree Name

Civil Engineering

Level of Degree

Masters

Department Name

Civil Engineering

First Committee Member (Chair)

Shen, Yu-Lin

Second Committee Member

Gerstle, Walter

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