Geopolymer composites and their applications in stress wave mitigation

Cho, Shinhu

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Description

Title

Geopolymer composites and their applications in stress wave mitigation

Author(s)

Cho, Shinhu

Issue Date

2015-07-16

Director of Research (if dissertation) or Advisor (if thesis)

Kriven, Waltraud M.

Doctoral Committee Chair(s)

Vakakis, Alexander F.

Committee Member(s)

• Shang, Jian Ku
• Mondal, Paramita

Department of Study

Mechanical Sci & Engineering

Discipline

Mechanical Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Geopolymer
• Sustainable Material

Abstract

In recent years, environmentally friendly materials have been the focus as alternatives to ordinary Portland cement (OPC), which generates about 6% of the total carbon dioxide emission in the world today and contributes to global warming. An alternative material to cement is aluminosilicate inorganic polymer, also known as “geopolymer” which emits about 80% less CO2 than OPC. Therefore, the chemical, mechanical, thermal and electrical properties of geopolymers have been of interest for the past two decades. The processes and microstructures of potassium-based geopolymer (K2O ∙ Al2O3 ∙ 4SiO2 ∙ 11H2O) have been studied by many researchers with various techniques. However, the brittleness and relatively lower strength limited the use of geopolymer in certain applications. Therefore, short carbon fibers (60 and 100 μm) have been introduced to reinforce the mechanical properties of potassium based geopolymer. The proper mixing and drying conditions of carbon fiber reinforced potassium geopolymer (Cf KGP) were determined since the mechanical properties varied in wide range depending on the drying conditions. Various static mechanical tests (flexure, uniaxial compression, hardness, toughness and biaxial tensile tests) and statistical analyses of brittle fractures (Weibull distribution) have been performed to investigate the optimal mechanical strengths of Cf KGP composites. In addition to the static measurements, the Young’s and shear moduli of Cf KGP have been measured by dynamic methods such as impulse excitation (IE) and resonant ultrasound spectroscopy (RUS) and compared with various theoretical models. Graphene nanoplatelets have high mechanical, electrical and thermal properties that can significantly improve the desired properties of composites at even low contents. 1, 2 and 3 wt% of graphene nanoplatelet-reinforced, potassium geopolymers (GNP KGP) were prepared and their microstructures were investigated by SEM, XRD and Raman spectroscopy. The mechanical properties such as flexure strength, Weibull modulus, Vickers hardness and Young’s modulus were measured by four-point flexure, microindentation and impulse excitation testing. In addition to mechanical properties, the electrical and thermal properties of GNP KGP were investigated by measuring electrical resistances and thermal conductivities. Moreover, silicon functionalized graphene nanoplatelets (sGNP) were prepared in order to enhance interfacial bonding between GNP and the geopolymer matrix. The various mechanical properties of sGNP KGP were measured and compared with GNP KGP, in order to investigate the effect of silicon functionalization. Due to their similarity with concrete, geopolymers have been mainly used as structural materials. With documented chemical and mechanical properties of geopolymers, their use could be expanded to applications in many disciplines. In this work, geopolymers were used as granular media and displayed interesting dynamic behavior for stress wave mitigation and as acoustic metamaterials. The fabrication of geopolymer beads was achieved by simple injection into a Polydimethylsiloxane (PDMS) polymer mold. Based on the mechanical properties of geopolymers, the dynamic responses of homogeneous and dimer chains were theoretically predicted and experimentally investigated under impulse excitation. By substituting metal beads for geopolymer beads which are 6 times lighter, a linear array of lightweight granular media was created to mitigate the effects of a stress wave.

Graduation Semester

2015-8

Type of Resource

text

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Copyright and License Information

Copyright 2015 Shinhu Cho

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