ASU Electronic Theses and Dissertations
This collection includes most of the ASU Theses and Dissertations from 2011 to present. ASU Theses and Dissertations are available in downloadable PDF format; however, a small percentage of items are under embargo. Information about the dissertations/theses includes degree information, committee members, an abstract, supporting data or media.
In addition to the electronic theses found in the ASU Digital Repository, ASU Theses and Dissertations can be found in the ASU Library Catalog.
Dissertations and Theses granted by Arizona State University are archived and made available through a joint effort of the ASU Graduate College and the ASU Libraries. For more information or questions about this collection contact or visit the Digital Repository ETD Library Guide or contact the ASU Graduate College at gradformat@asu.edu.
Displaying 1 - 3 of 3
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- All Subjects: Drying
- All Subjects: plastic viscosity
- Creators: Mobasher, Barzin
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 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
Description
Concrete develops strength rapidly after mixing and is highly influenced by temperature and curing process. The material characteristics and the rate of property development, along with the exposure conditions influences volume change mechanisms in concrete, and the cracking propensity of the mixtures. Furthermore, the structure geometry (due to restraint as well as the surface area-to-volume ratio) also influences shrinkage and cracking. Thus, goal of this research is to better understand and predict shrinkage cracking in concrete slab systems under different curing conditions. In this research, different concrete mixtures are evaluated on their propensity to shrink based on free shrinkage and restrained shrinkage tests.Furthermore, from the data obtained from restrained ring test, a casted slab is measured for shrinkage. Effects of different orientation of restraints are studied and compared to better understand the shrinking behavior of the concrete mixtures. The results show that the maximum shrinkage is near the edges of the slab and decreases towards the center. Shrinkage near the edges with no restraint is found out to be more than the shrinkage towards the edges with restraining effects.
ContributorsNimbalkar, Atharwa Samir (Author) / Neithalath, Narayanan (Thesis advisor) / Mobasher, Barzin (Thesis advisor) / Rajan, Subramaniam (Committee member) / Arizona State University (Publisher)
Created2023
Description
The need for sustainability in construction has encouraged scientists to develop novel environmentally friendly materials. The use of supplementary cementitious materials was one such initiative which aided in enhancing the fresh and hardened concrete properties. This thesis aims to explore the understanding of the early age rheological properties of such cementitious systems.
The first phase of the work investigates the influence of supplementary cementitious materials (SCM) in combination with ordinary Portland cement (OPC) on the rheological properties of fresh paste with and without the effect of superplasticizers. Yield stress, plastic viscosity and storage modulus are the rheological parameters which were evaluated for all the design mixtures to fundamentally understand the synergistic effects of the SCM. A time-dependent study was conducted on these blends to explore the structure formation at various time intervals which explains the effect of hydration in conjecture to its physical stiffening. The second phase focuses on the rheological characterization of novel iron powder based binder system.
The results of this work indicate that the rheological characteristics of cementitious suspensions are complex, and strongly dependent on several key parameters including: the solid loading, inter-particle forces, shape of the particle, particle size distribution of the particles, and rheological nature of the media in which the particles are suspended. Chemical composition and reactivity of the material play an important role in the time-dependent rheological study.
A stress plateau method is utilized for the determination of rheological properties of concentrated suspensions, as it better predicts the apparent yield stress and is shown to correlate well with other viscoelastic properties of the suspensions. Plastic viscosity is obtained by calculating the slope of the stress-strain rate curve of ramp down values of shear rates. In oscillatory stress measurements the plateau obtained within the linear visco-elastic region was considered to be the value for storage modulus.
Between the different types of fly ash, class F fly ash indicated a reduction in the rheological parameters as opposed to class C fly ash that is attributable to the enhanced ettringite formation in the latter. Use of superplasticizer led to a huge influence on yield stress and storage modulus of the paste due to the steric hindrance effect.
In the study of iron based binder systems, metakaolin had comparatively higher influence than fly ash on the rheology due to its tendency to agglomerate as opposed to the ball bearing effect observed in the latter. Iron increment above 60% resulted in a decrease in all the parameters of rheology discussed in this thesis. In the OPC-iron binder, the iron behaved as reinforcements yielding higher yield stress and plastic viscosity.
The first phase of the work investigates the influence of supplementary cementitious materials (SCM) in combination with ordinary Portland cement (OPC) on the rheological properties of fresh paste with and without the effect of superplasticizers. Yield stress, plastic viscosity and storage modulus are the rheological parameters which were evaluated for all the design mixtures to fundamentally understand the synergistic effects of the SCM. A time-dependent study was conducted on these blends to explore the structure formation at various time intervals which explains the effect of hydration in conjecture to its physical stiffening. The second phase focuses on the rheological characterization of novel iron powder based binder system.
The results of this work indicate that the rheological characteristics of cementitious suspensions are complex, and strongly dependent on several key parameters including: the solid loading, inter-particle forces, shape of the particle, particle size distribution of the particles, and rheological nature of the media in which the particles are suspended. Chemical composition and reactivity of the material play an important role in the time-dependent rheological study.
A stress plateau method is utilized for the determination of rheological properties of concentrated suspensions, as it better predicts the apparent yield stress and is shown to correlate well with other viscoelastic properties of the suspensions. Plastic viscosity is obtained by calculating the slope of the stress-strain rate curve of ramp down values of shear rates. In oscillatory stress measurements the plateau obtained within the linear visco-elastic region was considered to be the value for storage modulus.
Between the different types of fly ash, class F fly ash indicated a reduction in the rheological parameters as opposed to class C fly ash that is attributable to the enhanced ettringite formation in the latter. Use of superplasticizer led to a huge influence on yield stress and storage modulus of the paste due to the steric hindrance effect.
In the study of iron based binder systems, metakaolin had comparatively higher influence than fly ash on the rheology due to its tendency to agglomerate as opposed to the ball bearing effect observed in the latter. Iron increment above 60% resulted in a decrease in all the parameters of rheology discussed in this thesis. In the OPC-iron binder, the iron behaved as reinforcements yielding higher yield stress and plastic viscosity.
ContributorsInbasekaran, Aditya (Author) / Neithalath, Narayanan (Thesis advisor) / Rajan, Subramaniam D. (Committee member) / Mobasher, Barzin (Committee member) / Arizona State University (Publisher)
Created2016