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Description
Concrete is the most widely used infrastructure material worldwide. Production of portland cement, the main binding component in concrete, has been shown to require significant energy and account for approximately 5-7% of global carbon dioxide production. The expected continued increased use of concrete over the coming decades indicates this is

Concrete is the most widely used infrastructure material worldwide. Production of portland cement, the main binding component in concrete, has been shown to require significant energy and account for approximately 5-7% of global carbon dioxide production. The expected continued increased use of concrete over the coming decades indicates this is an ideal time to implement sustainable binder technologies. The current work aims to explore enhanced sustainability concretes, primarily in the context of limestone and flow. Aspects such as hydration kinetics, hydration product formation and pore structure add to the understanding of the strength development and potential durability characteristics of these binder systems. Two main strategies for enhancing this sustainability are explored in this work: (i) the use of high volume limestone in combination with other alternative cementitious materials to decrease the portland cement quantity in concrete and (ii) the use of geopolymers as the binder phase in concrete. The first phase of the work investigates the use of fine limestone as cement replacement from the perspective of hydration, strength development, and pore structure. The nature of the potential synergistic benefit of limestone and alumina will be explored. The second phase will focus on the rheological characterization of these materials in the fresh state, as well as a more general investigation of the rheological characterization of suspensions. The results of this work indicate several key ideas. (i) There is a potential synergistic benefit for strength, hydration, and pore structure by using alumina and in portland limestone cements, (ii) the limestone in these systems is shown to react to some extent, and fine limestone is shown to accelerate hydration, (iii) rheological characteristics of cementitious suspensions are complex, and strongly dependent on several key parameters including: the solid loading, interparticle forces, surface area of the particles present, particle size distribution of the particles, and rheological nature of the media in which the particles are suspended, and (iv) stress plateau method is proposed for the determination of rheological properties of concentrated suspensions, as it more accurately predicts apparent yield stress and is shown to correlate well with other viscoelastic properties of the suspensions.
ContributorsVance, Kirk (Author) / Neithalath, Narayanan (Thesis advisor) / Rajan, Subramaniam D. (Committee member) / Mobasher, Barzin (Committee member) / Chawla, Nikhilesh (Committee member) / Marzke, Robert (Committee member) / Arizona State University (Publisher)
Created2014
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Description
Being a remarkably versatile and inexpensive building material, concrete has found tremendous use in development of modern infrastructure and is the most widely used material in the world. Extensive research in the field of concrete has led to the development of a wide array of concretes with applications ranging from

Being a remarkably versatile and inexpensive building material, concrete has found tremendous use in development of modern infrastructure and is the most widely used material in the world. Extensive research in the field of concrete has led to the development of a wide array of concretes with applications ranging from building of skyscrapers to paving of highways. These varied applications require special cementitious composites which can satisfy the demand for enhanced functionalities such as high strength, high durability and improved thermal characteristics among others.

The current study focuses on the fundamental understanding of such functional composites, from their microstructural design to macro-scale application. More specifically, this study investigates three different categories of functional cementitious composites. First, it discusses the differences between cementitious systems containing interground and blended limestone with and without alumina. The interground systems are found to outperform the blended systems due to differential grinding of limestone. A novel approach to deduce the particle size distribution of limestone and cement in the interground systems is proposed. Secondly, the study delves into the realm of ultra-high performance concrete, a novel material which possesses extremely high compressive-, tensile- and flexural-strength and service life as compared to regular concrete. The study presents a novel first principles-based paradigm to design economical ultra-high performance concretes using locally available materials. In the final part, the study addresses the thermal benefits of a novel type of concrete containing phase change materials. A software package was designed to perform numerical simulations to analyze temperature profiles and thermal stresses in concrete structures containing PCMs.

The design of these materials is accompanied by material characterization of cementitious binders. This has been accomplished using techniques that involve measurement of heat evolution (isothermal calorimetry), determination and quantification of reaction products (thermo-gravimetric analysis, x-ray diffraction, micro-indentation, scanning electron microscopy, energy-dispersive x-ray spectroscopy) and evaluation of pore-size distribution (mercury intrusion porosimetry). In addition, macro-scale testing has been carried out to determine compression, flexure and durability response. Numerical simulations have been carried out to understand hydration of cementitious composites, determine optimum particle packing and determine the thermal performance of these composites.
ContributorsArora, Aashay (Author) / Neithalath, Narayanan (Thesis advisor) / Rajan, Subramaniam D. (Committee member) / Mobasher, Barzin (Committee member) / Chawla, Nikhilesh (Committee member) / Hoover, Christian G (Committee member) / Arizona State University (Publisher)
Created2018
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Description
It is the intent of this research to determine the feasibility of utilizing industrial byproducts in cementitious systems in lieu of Portland Cement to reduce global CO2 emissions. Class C and Class F Fly Ash (CFA and FFA, respectively) derived from industrial coal combustion were selected as the replacement materials

It is the intent of this research to determine the feasibility of utilizing industrial byproducts in cementitious systems in lieu of Portland Cement to reduce global CO2 emissions. Class C and Class F Fly Ash (CFA and FFA, respectively) derived from industrial coal combustion were selected as the replacement materials for this study. Sodium sulfate and calcium oxide were used as activators. In Part 1 of this study, focus was placed on high volume replacement of OPC using sodium sulfate as the activator. Despite improvements in heat generation for both CFA and FFA systems in the presence of sulfate, sodium sulfate was found to have adverse effects on the compressive strength of CFA mortars. In the CFA mixes, strength improved significantly with sulfate addition, but began to decrease in strength around 14 days due to expansive ettringite formation. Conversely, the addition of sulfate led to improved strength for FFA mixes such that the 28 day strength was comparable to that of the CFA mixes with no observable strength loss. Maximum compressive strengths achieved for the high volume replacement mixes was around 40 MPa, which is considerably lower than the baseline OPC mix used for comparison. In Part 2 of the study, temperature dependency and calcium oxide addition were studied for sodium sulfate activated systems composed of 100% Class F fly ash. In the presence of sulfate, added calcium increased reactivity and compressive strength at early ages, particularly at elevated temperatures. It is believed that sulfate and calcium react with alumina from fly ash to form ettringite, while heat overcomes the activation energy barrier of fly ash. The greatest strengths were obtained for mixes containing the maximum allowed quantity of calcium oxide (5%) and sodium sulfate (3%), and were around 12 MPa. This is a very low compressive strength relative to OPC and would therefore be an inadequate substitute for OPC needs.
Created2014-05
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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

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
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Description
This dissertation aims at developing novel materials and processing routes using alkali activated aluminosilicate binders for porous (lightweight) geopolymer matrices and 3D-printing concrete applications. The major research objectives are executed in different stages. Stage 1 includes developing synthesis routes, microstructural characterization, and performance characterization of a family of economical, multifunctional

This dissertation aims at developing novel materials and processing routes using alkali activated aluminosilicate binders for porous (lightweight) geopolymer matrices and 3D-printing concrete applications. The major research objectives are executed in different stages. Stage 1 includes developing synthesis routes, microstructural characterization, and performance characterization of a family of economical, multifunctional porous ceramics developed through geopolymerization of an abundant volcanic tuff (aluminosilicate mineral) as the primary source material. Metakaolin, silica fume, alumina powder, and pure silicon powder are also used as additional ingredients when necessary and activated by potassium-based alkaline agents. In Stage 2, a processing route was developed to synthesize lightweight geopolymer matrices from fly ash through carbonate-based activation. Sodium carbonate (Na2CO3) was used in this study to produce controlled pores through the release of CO2 during the low-temperature decomposition of Na2CO3. Stage 3 focuses on 3D printing of binders using geopolymeric binders along with several OPC-based 3D printable binders. In Stage 4, synthesis and characterization of 3D-printable foamed fly ash-based geopolymer matrices for thermal insulation is the focus. A surfactant-based foaming process, multi-step mixing that ensures foam jamming transition and thus a dry foam, and microstructural packing to ensure adequate skeletal density are implemented to develop foamed suspensions amenable to 3D-printing. The last stage of this research develops 3D-printable alkali-activated ground granulated blast furnace slag mixture. Slag is used as the source of aluminosilicate and shows excellent mechanical properties when activated by highly alkaline activator (NaOH + sodium silicate solution). However, alkali activated slag sets and hardens rapidly which is undesirable for 3D printing. Thus, a novel mixing procedure is developed to significantly extend the setting time of slag activated with an alkaline activator to suit 3D printing applications without the use of any retarding admixtures. This dissertation, thus advances the field of sustainable and 3D-printable matrices and opens up a new avenue for faster and economical construction using specialized materials.
ContributorsAlghamdi, Hussam Suhail G (Author) / Neithalath, Narayanan (Thesis advisor) / Rajan, Subramaniam D. (Committee member) / Mobasher, Barzin (Committee member) / Abbaszadegan, Morteza (Committee member) / Bhate, Dhruv (Committee member) / Arizona State University (Publisher)
Created2019