چكيده به لاتين
Saline soils usually cannot meet the needs of engineering projects due to their inappropriate geotechnical characteristics. For this reason, in terms of geotechnical engineering, they are always known as one of the problematic soils in the world. Portland cement, as the most widely used material in the field of chemical soil improvement, in addition to having harmful environmental effects (including high energy consumption and greenhouse gas emissions during its production), has limitations in terms of its use in saline soils. Because most of the past researches have pointed to the poor long-term mechanical strength of Portland cement stabilized saline soils. In recent years, alkali activated cements have been proposed as a new generation of chemical soil stabilizers. The use of alkali activated cement not only does not have the environmental problems caused by the production of Portland cement, but the raw materials that are usually used to produce this material are aluminosilicate materials such as industrial slag, construction waste and natural pozzolans, which can preserve the environment and can create added value for industrial waste and effective use of unused mines. Nevertheless, in order to use alkali activated cements as chemical soil stabilizers, the performance of these types of cements against harmful environmental conditions, including saline soils, should be investigated. Therefore, in this research, the effects of sodium chloride on the microstructural and mechanical properties of cubic samples of Portland/alkali activated cement paste were investigated. Then, the effects of sodium chloride on the microstructural and mechanical properties of Portland cement and alkali activated Taftan pozzolan/slag stabilized sandy soil were investigated. Also, the effects of precursor type, slag replacement percentage, curing time and curing conditions, as well as the amount of sodium chloride on the unconfined compressive strength of the stabilized soil were investigated. In addition, microstructural analyses, including X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy (SEM) tests, were performed to understand the physical and chemical interaction of chloride ions and activated alkali cements. The results showed that activated alkali slag can be considered as a suitable alternative to Portland cement for soil improvement projects in saline environments. The increase in sodium chloride (NaCl) content up to 1 wt.% caused the strength development up to 244% in specimens with 50 and 100 wt.% slag and adding more NaCl had no significant effect on the strength in all curing conditions. Microstructural investigations showed that the replacement of volcanic ash with slag resulted in the formation of C-S-H and C-A-S-H gels that reduced the porosity of the samples and increased mechanical strength. Furthermore, surface adsorption and chemical encapsulation mechanisms co-occurred in stabilized soil samples containing slag and volcanic ash.
