Civil Engineering ETDs

Publication Date

Summer 6-8-2007

Abstract

Nanomaterials are defined by those whose characteristic length scale lies within the nanometer scale. Their extreme dimension achieves extraordinary mechanical properties superior to other micro and macro additives. The introduction of nanotechnology to Civil Engineering utilizes low volume inclusions of nanomaterials to alter the properties of conventionally used bulk materials. Polymer Concrete (PC) where epoxy polymer binders replace cement binders, has become a common repair material among many other application and often can be considered an alternative to Portland cement concrete (PCC). PC is often used in bridge deck overlays, manholes, machine foundations and repairs. Its diverse chemical composition and high flowability makes it a supreme candidate to take advantage of nanomaterials induced chemical and mechanical effects. This research effort is designated to examine the impact of various loadings of different nanomaterials on PC’s mechanical and microstructural properties. Nanomaterials used are alumina nanoparticles (ANPs), silica nanoparticles (SNPs), pristine and carboxyl multi-walled carbon nanotubes (P-MWCNTs and COOH-MWCNTs). The polymer epoxy matrix chosen are Siloxane and Novolac epoxies used by the industry for bridge deck overlays and repairs respectively. Mechanical tests included flowability, tension, compression, flexure, fracture toughness, slant shear, and fatigue tests alongside electrical conductivity monitoring. Microstructural investigation vi included scanning electron microscope (SEM), dynamic modulus analyzer (DMA), and Fourier transform infrared spectrograph (FTIR). Analytical study of rule of mixture, stiffness mismatch and true shear stresses using finite element modeling (FEM) were also utilized. Dispersion was performed using magnetic stirring and ultrasonication which were verified in all PCNC mixes using SEM. Mechanical and microstructural tests show that the investigated nanomaterials at different contents generate varying mechanical and chemical effects in PC. Significant difference between 1D and 0D nanomaterials and between functionalized and non-functionalized are observed. Nevertheless, PC nanocomposites (PCNC) showed significant improvements in mechanical performance. All PCNC samples exhibited appreciable tensile strength between 9 – 15 MPa and large ductility up to 5.5% strain at failure representing an order of magnitude improvement from PCC. Hybrid MWCNTs mixes showed the best tensile properties of all suggested mixes. Further investigation using DMA and FTIR tests showed increased crosslinking with increasing COOH content due to carbonyl group formations. Improvements in fracture toughness were also recorded for all PCNC up to 80% from neat. PC and PCNC showed distinctive non-linear behavior that is best quantified using QBFM. Fatigue life due to ductility and fracture toughness improvements increased by 55%. The compressive strength of all PCNC ranged between 23 MPa and 60 MPa and in general nanomaterials resulted in a decrease in compressive strength. The bond strength of PC also increased by maximum of 51%. FTIR analysis showed that the bond strength of PCNC is highly dependent on chemical interaction with the interface. The bond strength is also severely affected by the stiffness mismatch and Poisson’s ratio as shown by FEM and analytical mechanics causing up to 130% increase in bond strength. The proposed PCNC can serve as smart material enabling structural health monitoring (SHM) and is highly suitable as a structural material specifically for earthquakes.

Keywords

Polymer concrete, nanomaterials, Carbon nanotubes, alumina nanoparticles, stiffness mismatch, mechanical properties

Document Type

Thesis

Language

English

Degree Name

Civil Engineering

Level of Degree

Masters

Department Name

Civil Engineering

First Committee Member (Chair)

Mahmoud Reda Taha

Second Committee Member

Yu-Lin Shen

Third Committee Member

John Stormont

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