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Description
The main objective of this study is to numerically investigate: (i) the ionic transport, especially chloride ion penetration into cementitious materials under imposed electric fields, and (ii) moisture transport through cracked concretes as a function of the crack geometry. Numerical methods were implemented to simulate the ionic transport process, based

The main objective of this study is to numerically investigate: (i) the ionic transport, especially chloride ion penetration into cementitious materials under imposed electric fields, and (ii) moisture transport through cracked concretes as a function of the crack geometry. Numerical methods were implemented to simulate the ionic transport process, based on coupling the Nernst-Planck equation and Poisson's equation to account for transport dominated by electromigration. This mathematical model was also modified to account for the chloride binding mechanism (physical and chemical trapping of chlorides by the cement hydrates) and the concentration dependence of the diffusion coefficient of each ion in the transport process. To validate the numerical model, experimental data from a companion work was used in this study. The non-steady state migration test, which is one of the common accelerated chloride ion transport test, is numerically simulated. The simulation provides a linear relationship between ionic concentration and ionic flux, which indicates that the diffusion part is negligible under a strong external voltage environment. The numerical models along with adjustments for the concentration-dependent diffusion coefficients, a pore structure factor (from electrical measurements) and chloride binding considerations are found to be successful in predicting the chloride penetration depth into plain and modified concretes under imposed electrical potentials. Moisture transport through cracked concrete was examined in the second part of this thesis. To better understand the crack's influence on the permeability, modified Louis' equation was chosen to relate the permeability with crack characteristics. 3D concrete crack models were developed using a MATLAB program with distinct crack tortuosities, roughnesses and sizes. As a comparison, Navier-Stokes equation and the Lattice Boltzmann method were also applied on the 3D model of the cracked concrete to evaluate their permeability. The methodology developed here is expected to be useful in understanding the influence of cracking on moisture transport, and when properly coupled with an ionic transport model that will be further developed, helps comprehensively understand the coupling effects of moisture and ionic transport on deterioration in concrete structures.
ContributorsYang, Pu (Author) / Neithalath, Narayanan (Thesis advisor) / Dharmarajan, Subramaniam (Committee member) / Mobasher, Barzin (Committee member) / Arizona State University (Publisher)
Created2014
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Description
The main objective of this study is to investigate drying properties and plastic shrinkage cracking resistance of fresh cement-based pastes reinforced with fibers and textiles. Naturally occurring mineral wollastonite has been studied independently as well as in combination with AR-glass textile. A series of blended mixes with Portland cement and

The main objective of this study is to investigate drying properties and plastic shrinkage cracking resistance of fresh cement-based pastes reinforced with fibers and textiles. Naturally occurring mineral wollastonite has been studied independently as well as in combination with AR-glass textile. A series of blended mixes with Portland cement and wollastonite nano-fibers were developed and tested under low vacuum conditions to simulate severe evaporation conditions and expedite the drying process causing plastic shrinkage cracks. Cumulative moisture loss, evaporation rates, and diffusivity were analyzed by means of a 2-stage diffusion simulation approach, developed previously in Arizona State University. Effect of fiber-matrix interaction on the transport properties of the composite were evaluated using the existing approach. Morphology of the cracked surface was investigated by the means of image analysis wherein length, width, area and density of the cracks were computed to help characterize the contribution of fiber and textile in the cracking phenomenon. Additionally, correlation between cumulative moisture loss and crack propagation was attempted. The testing procedures and associated analytical methods were applied to evaluate effectiveness of four wollastonite fiber sizes and also a hybrid reinforcement system with alkali-resistant glass (ARG) textile in improving shrinkage cracking related parameters. Furthermore, the experimental and analytical approach was extended to magnified version of the existing shrinkage testing set-up to study the size effect of these composites when subjected to matching drying conditions. Different restraining mechanisms were used to study the simulation of the cracking phenomena on a larger specimen. Paste and mortar formulations were developed to investigate size effect on shrinkage resistance of cementitious composites.
ContributorsKachala, Robert (Author) / Mobasher, Barzin (Thesis advisor) / Dharmarajan, Subramaniam (Committee member) / Neithalath, Narayanan (Committee member) / Arizona State University (Publisher)
Created2014
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Description
The main objective of this study is to investigate the behaviour and applications of strain hardening cement composites (SHCC). Application of SHCC for use in slabs of common configurations was studied and design procedures are prepared by employing yield line theory and integrating it with simplified tri-linear model developed in

The main objective of this study is to investigate the behaviour and applications of strain hardening cement composites (SHCC). Application of SHCC for use in slabs of common configurations was studied and design procedures are prepared by employing yield line theory and integrating it with simplified tri-linear model developed in Arizona State University by Dr. Barzin Mobasher and Dr. Chote Soranakom. Intrinsic material property of moment-curvature response for SHCC was used to derive the relationship between applied load and deflection in a two-step process involving the limit state analysis and kinematically admissible displacements. For application of SHCC in structures such as shear walls, tensile and shear properties are necessary for design. Lot of research has already been done to study the tensile properties and therefore shear property study was undertaken to prepare a design guide. Shear response of textile reinforced concrete was investigated based on picture frame shear test method. The effects of orientation, volume of cement paste per layer, planar cross-section and volume fraction of textiles were investigated. Pultrusion was used for the production of textile reinforced concrete. It is an automated set-up with low equipment cost which provides uniform production and smooth final surface of the TRC. A 3-D optical non-contacting deformation measurement technique of digital image correlation (DIC) was used to conduct the image analysis on the shear samples by means of tracking the displacement field through comparison between the reference image and deformed images. DIC successfully obtained full-field strain distribution, displacement and strain versus time responses, demonstrated the bonding mechanism from perspective of strain field, and gave a relation between shear angle and shear strain.
ContributorsAswani, Karan (Author) / Mobasher, Barzin (Thesis advisor) / Dharmarajan, Subramaniam (Committee member) / Neithalath, Narayanan (Committee member) / Arizona State University (Publisher)
Created2014