Document Type

Thesis - Open Access

Award Date

2020

Degree Name

Master of Science (MS)

Department

Civil and Environmental Engineering

First Advisor

Rouzbeh Ghabchi

Keywords

Asphalt, Cellulose Nanofibers, Electrospinning, Polymer Modified Asphalt Binder, RAP

Abstract

Findings of a study conducted on asphalt binders and mixes modified by addition of cellulose nanofiber (CNF) to evaluate the feasibility of them as an additive is presented in the current thesis. Cellulose Acetate (CA) is an ester of cellulose and is obtained by the reaction of cellulose with acetic anhydride and acetic acid in the presence of sulfuric acid. Due to its high temperature sensitivity, high ductility, large surface area, high strain resistance, and low electrical resistivity, cellulose acetate can be used for several application. The question is if CNF can be used as an additive in the asphalt, with the goal of improving the pavement properties. Asphalt binder and asphalt mix properties, including adhesion, resistance to cracking by measurement of energy absorption, viscosity, moisture induced damage, fatigue resistance, and rutting were evaluated by conducting rotation viscometer (RV) test, Izod impact strength test, binder bond strength (BBS) test, tensile strength ratio (TSR) test, semi-circular bend (SCB) test, and Hamburg wheel tracking (HWT) test. Cellulose nanofiber (CNF) production and evaluation, asphalt binders containing cellulose nanofiber evaluation, and asphalt mixes containing cellulose nanofiber evalujation are the three major parts of the study. For the CNF production and evaluation, two different electrospinning techniques as well as five different solutions were evaluated to find out which technique and solution produced the nanofiber suitable for the study. CNF fibers were produced with two different electrospinning techniques, namely static and rotating electrospinning. Produced fibers’ morphology, microstructure and strength properties were evaluated by conducting laser scan microscopy (LSM), scanning electron microscopy (SEM), and tensile strength test. After fiber production and evaluation, the CNF produced with the suitable technique was selected and was mixed with asphalt binder and asphalt mix for further evaluation. Three different asphalt binders, namely PG 58-28, PG 64-34, and PG 70-28 were used for the asphalt binder evaluation. For the asphalt mix evaluation, a hot mix asphalt (HMA) containing 20% reclaimed asphalt pavement (RAP) was used. From the fiber production and evaluation, it was found that fibers produced using static electrospinning from a solution containing CA plus the solvent system acetone/water (Solution 5) and tested at a non-production direction had the highest average tensile strength. It was found that the average tensile strength for Solution 5 was 9.05 N, the highest among other alternatives. In addition to the average tensile strength of the produced fiber, the roughness and the average dimeter were evaluated using LSM and SEM techniques, respectively. It was found from these tests that the selected CNF had the roughest texture and the highest average diameter (1.756 μm). Overall, electrospun CNF produced using the abovementioned solution and technique was the roughest, the thickest and the strongest among all the tested fibers. Based on that it was the selected CNF to be used as an asphalt additive to improve the mechanical properties of asphalt binders and asphalt mixes. For the asphalt binder evaluation, blends of three different binders, namely PG 58- 28, PG 64-34, and PG 70-28 were mixed with different concentrations of CNF (0%, 0.2%, 0.3%, 0.5% and 0.7% by the weight of binder). For RV and BBS tests, binder blends containing 0%, 0.3%, and 0.7% CNF were used. For Izod impact strength binder blends containing 0%, 0.2%, 0.3%, 0.5% and 0.7% CNF by the weight of binder were used. It was found that the addition of CNF to asphalt binders resulted in an increase in viscosity of the asphalt binders, the higher the concentration of added CNF the higher the viscosity of the binder. A similar trend of variation in fracture toughness values with the increase in CNF concentration was also observed from Izod impact strength test. Furthermore, the BBS test results showed that for the majority of the cases addition of 0.7% CNF resulted in a higher BBS ratio compared to other combinations. It was found that for all the tested aggregates, granite, quartzite, and gravel, in contact with a PG 58-28 had the highest BBS ratio. For quartzite and gravel the addition of 0.3% CNF resulted in a reduction or no chance in BBS ratio values compared to binders without any CNF. However, for granite the addition of 0.3% and 0.7% CNF resulted in almost the same increase in BBS ratio value compared to the neat binder. The highest BBS ratio found was for PG 70-28 +0.7 CNF when tested in gravel. For the asphalt mix evaluation, three different concentration of fibers on the RAP 20 Mix were evaluated (RAP 20 containing 0%, 0.3%, and 0.7% cellulose acetate nanofibers). For SCB test, used to evaluate the cracking resistance through determining the critical strain energy release rate (Jc), the addition of fibers improved the Jc value. It was found that the higher amount of added fibers resulted in the higher Jc value. Since the SCB test relates the Jc value with the fatigue cracking resistance, RAP20+0.7% CNF had the highest fatigue cracking resistance. For the TSR test, it was found that the addition of fibers decreases the TSR ratio. The TSR test evaluates the resistance to moisture-induced damage of the mix. Based only on the TSR ratio, the addition of CNF causes the mix to be more susceptible to moisture induced damage. However, it was found that even though the TRS ratio decreases the addition of 0.3% and 0.7% CNF improved the dry conditioned tensile strength and the addition of 0.7% CNF improved the moisture conditioned tensile strength. So, based on the abovementioned fact it can say that the addition of fibers improves the resistance to moisture induced damage. For the HWT test, used to evaluate the moisture induced damage through determining the rutting and the stripping point, the addition of 0.7% CNF improved the rutting and increased the stripping point value. However, the addition of 0.3% CNF caused the asphalt mix to perform worse than the control asphalt mix. It was found that the results of HWT test, TSR test, and BBS test supports the idea that the addition of fibers improve the moisture induced damage of the asphalt. However, an optimum quantity of fibers needs to be added to the asphalt for it to start performing better. It was proved that 0.3% CNF was not enough for the asphalt to perform better, it caused the opposite, the asphalt performs worse. From the results of Izod impact strength test and SCB it was clear that the addition of any quantity of fiber improved the resistance to fatigue cracking. For the RV test it was proved that the addition of CNF will requires more compaction efforts while paving. Overall, the study promoted valuable information that will help the development of cellulose acetate nanofibers as additives in asphalt binder and asphalt mix. However, future research is necessary to further understand and master the production of nanofibers and to allow a better selection of CNF to be added onto the asphalt.

Library of Congress Subject Headings

Nanofibers.
Cellulose fibers.
Asphalt -- Additives -- Testing.
Pavements, Asphalt -- Additives -- Testing.
Binders (Materials)
Asphalt -- Mixing.

Format

application/pdf

Number of Pages

155

Publisher

South Dakota State University

Rights

In Copyright - Educational Use Permitted
http://rightsstatements.org/vocab/InC-EDU/1.0/

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