Engineering properties and microstructural analysis of a new developed geopolymer mortar

Recently, the increasing trend of industries is considered one of the major reasons for global warming. This phenomenon is mainly based on the emissions of greenhouse gases, those gases are formed as a by-product of some main metals and materials. Portland cement production is one of those production processes and is not classified among the sustainable products in terms of emissions after production. While considered responsible for about 7% of the total CO2 emissions around the world, the process of producing cement is presented nowadays as one of the most environmentally harmful production processes. Producing one ton of cement emits almost one ton of CO2. This emission pattern is always prone to increase due to the inevitable need for construction works. These facts led the research community to investigate the possibility of manufacturing sustainable alternatives which are satisfactory in terms of strength, long-term properties, environmental feasibility and economical use. So many research attempts have been carried out in order to achieve a partial or a complete replacement to Portland cement with waste materials and industrial by-products, thus, acquiring a binding system which is comparable to the cementitious one. Some waste materials and industrial by-products possess pozzolanic properties which are used to achieve the aforementioned goals. Pozzolanic reactivity is used to obtain a binder with good properties and significant ease of application. Among the alternative binding matrices which were investigated, Geopolymers was presented as a promising binder since they were comparable to the cementitious system in all aspects. Those inorganic polymers have exhibited a significant improvement in terms of strength, long-term properties, and sustainability characteristics. xii A silica-alumina rich source is the main precursor which is required in the production process of geopolymers in order to form the main geopolymeric bonds, namely Si-O and Al-O bonds. This means that the previously mentioned pozzolanic materials are the most proper materials to be used in this process. the precursor is then reactivated in an alkaline medium which is formed by mixing the precursor with chemical activators. Fly ash, as one of the most reactive pozzolans in the construction section, has been used successfully in producing geopolymers due to the good properties that it has, also, its availability represents an encouraging factor in this concern In this research, an investigation will be made in order to evaluate the effect of different parameters such as filling materials, the dosage of chemical activator, partial replacement with silica fume and inclusion of fibers on the performance of the final produced fly ash based geopolymer mortars. The tests which were performed in this investigation were strength properties tests, physical aspects tests, abrasion resistance, non-destructive ultrasonic pulse velocity test, resistance to freeze-thaw cycles, drying shrinkage test and energy absorption rate. Also, a microstructural characterization was conducted in order to observe the internal composition of the geopolymeric matrix and identify the degree of compactness, scanning electron microscopy (SEM), X-ray diffraction and X-ray micro-CT scan tests were performed for this purpose. Based on the investigation parameters, the research was categorized into three parts. the first category investigated the effect of using various filling materials and two different activator concentrations, the second category studied the effect of using silica fume as a partial replacement with fly ash, whereas the third category evaluated the behavior of the matrix with the inclusion of fibers. In all of the studied categories, the results were compared were compared to a cementitious control sample. In general, the results revealed the fact that geopolymer was an active alternative to Portland cement in terms of all properties, the degree of microstructural bonding between the parts of the manufactured matrix resulted in better properties when compared to those of the cementitious sample. The results of the performed tests indicated that fabricating geopolymer samples results in a binding system with outstanding properties and applicable production process.