Investigation of mechanical properties of clayey soils using fly ash and blast furnace slag based geopolymer

In recent years, there has been a noticeable increase in infrastructure and superstructure projects due to rapid population growth. Clayey soils are regarded as problematic soils because of their poor engineering characteristics. Therefore, in order to keep up with the growth of the infrastructure and construction sectors, these weak characteristics must be improved. One of the most widely used soil stabilization methods today is to improve the properties of the soil by adding various additives. Due to the negative environmental effects of Portland cement and lime used in soil improvement, they have been replaced in recent years by environmentally friendly geopolymers. In this study, the effects of fly ash and blast furnace slag based geopolymer on the mechanical properties of high plasticity clay soils through geopolymerization were investigated. For this purpose, experimental studies were carried out using the Taguchi Method. The Taguchi L16 orthogonal array was used with various amounts of class F fly ash (12%, 16%, 20%, and 24%), blast furnace slag (8%, 10%, 12%, and 14%), and alkaline hydroxide solution NaOH molarity (6, 8, 10, and 12). Unconfined compressive strength (UCS) and California bearing ratio (CBR) tests were carried out on geopolymer soil samples prepared at optimum moisture content and maximum dry density after 7 and 28 days of curing. Additionally, permeability tests were performed after 28 days of curing. The effects of the variables on the experimental results were determined using S/N and variance analyses. In the strength tests, it was observed that the strengths increased as the molarity, blast furnace slag and fly ash content increased. At the end of the 7-28 days curing period, the lowest and highest strength values were found as 3.32 MPa - 3.92 MPa, 6.34 MPa - 7.96 MPa, respectively, in the unconfined compressive tests. As the curing time increased, the strength values increased. The most effective parameters on the strength were determined as sodium hydroxide (NaOH), blast furnace slag and fly ash content, respectively. According to the permeability test results, there is an inverse relationship between the permeability of the geopolymer soil and the percentage of additives (fly ash and blast furnace slag) as well as sodium hydroxide solution concentration. Furthermore, as the strength of the created geopolymer samples increased, the permeability decreased. Microstructural analysis of geopolymer soil samples was carried out using scanning electron microscopy (SEM) and (EDS). These findings are useful in promoting the production of geopolymers and encouraging their use in soil stabilization as an environmentally friendly alternative to cement.