Akademik Veri Yönetim Sistemi
Tezin Türü: Doktora
Tezin Yürütüldüğü Kurum: Yıldız Teknik Üniversitesi, İnşaat Fakültesi, İnşaat Mühendisliği Bölümü, Türkiye
Tezin Onay Tarihi: 2020
Tezin Dili: İngilizce
Öğrenci: Büşra AKTÜRK
Danışman: Ahmet Beşer Kızılkanat
Özet:
In view of today's environmental issues, the production process of construction materials must be designed and applied on the basis of minimum energy consumption. Considering the large amount of energy consumption and CO2 emissions (5-8%) caused by cement production, the necessity and importance of more sustainable material production have been increased over time. Alkali activated materials (AAMs) can be regarded as more environmental-friendly systems than ordinary Portland cement-based systems, since industrial wastes or byproducts such as slag, fly ash and/or natural pozzolanas that contain reactive silica and alumina have been used as raw materials in AAM production. Fineness and chemical composition of the precursor, type and concentration of the alkali activator, mixing procedure, and curing conditions are the main parameters affecting the characteristics of AAMs. The most common activators used in alkali activation are sodium/potassium hydroxides and sodium silicate as they have the dual effect of raising the pH and facilitating the dissolution of raw material. However, use of these activators may cause rapid setting, high drying shrinkage, and micro-cracking issues in practice. Moreover, high production costs and caustic nature make them less preferable. Therefore, in this study, it is aimed to use the naturally available sodium carbonate (NC) as main activator. NC is gaining attention as it is cost-effective, eco-friendly, and less harmful alternative to synthetic alkali hydroxides and silicates. Moreover, Turkey has the second largest NC reserves which increase the potential to use within this concept. However, prolonged setting time and delayed strength development are the main drawbacks of NC-activated systems. The aim of the current study is to produce a sustainable, applicable, and durable cementless construction material by utilizing slag and NC by overcoming the main drawbacks of NC. The first phase of the work focuses on accelerating the reaction mechanism of NC-activated slag (NCAS) by incorporating potential modifiers such as sodium hydroxide (NH) and calcium hydroxide (CH). The nature of the potential synergistic benefit of the modifiers is explored. The fresh-state characteristics such as setting time, yield stress, and plastic viscosity were determined. Strength development and the progress of hydration of the mixes are explained with the phase transformation and development of microstructural features through quantitative techniques such as thermogravimetric analysis and phase-identification techniques such as FTIR, and X-ray diffraction. The second phase of the work investigates the fracture response of plain and fiber-reinforced NCAS mortars through the double-K fracture toughness, fracture energy, and brittleness index. Moreover, drying shrinkage, water and chloride ion permeability of NCAS mixes are also investigated. Finally, all test results are statistically analysed and the optimum mixing proportions are obtained considering the desired multi-objective aims. The results of this work indicate several key ideas:
• CH and NH can be potential modifiers for achieving the desired setting time,
• Mechanical properties are improved with the incorporation of the modifiers,
• Low water and chloride ion permeability can be obtained for NCAS with the presence of the modifiers, especially CH,
• A substantial improvement is observed in terms of strength, pore structure, drying shrinkage and permeability in case of the incorporation of CH along with NH.
It is anticipated that the results obtained from this study will provide as yet unknown details on these novel binding systems.