Investigation of mechanical and microstructural properties of mortars containing obsidian, waste glass and fly ash activated with sodium hydroxide

Concrete is the most used material after water consumption in the world. The fact that concrete is used so much in the construction sector is due to the economic nature of concrete and its properties such as strength and durability. However, it is observed that cement, which is the raw material of concrete, causes harm to the environment due to the CO2 emissions that occur during its production and use, as well as the additives it provides to the concrete. Worldwide, the emission due to cement production and use constitutes 7-9% of all emissions. Considering such factors and considering sustainable technologies, cementless concrete technologies emerge as an alternative. Considering the damages they cause to the storage, environment and ecosystem of industrial and construction waste materials (fly ash and waste glass, etc.), the use of these materials in sustainable technologies prevents the harm of wastes to the environment and enables the development of new materials. In this study, mortar samples were produced by activating obsidian, waste glass, fly ash and 75%, 50% and 25% mixtures of these three materials with sodium hydroxide (NaOH). Mortar samples containing 13 different obsidian, waste glass and fly ash were prepared by using 12 molar (M) NaOH solution in the production of mortars. These produced mortar samples were divided into four different groups and each group was kept in ovens with temperatures of 75 °C, 90 °C, 105 °C and 120 °C for 72 hours. The obtained mortar samples were subjected to bending and compression tests at the end of 7, 28 and 90 days. Chemical analyzes of the binder materials used and microstructural examinations of the mortar samples were made on scanning electron microscope (SEM-EDS) images. As a result of this study, it has been seen that obsidian and waste glass can be used in the production of geopolymer. It has been determined that the mixtures of obsidian, waste glass and fly ash affect the bending and compressive strengths of each other. It has been observed that 90 °C temperature is the most suitable geopolymer production temperature. In addition, it has been observed that the materials used in different combinations work in harmony with each other and contribute to the development of mechanical properties. In the SEM and EDS analyzes, the highest strength values were determined in the samples with the most compact structure.