مهندسی عمران شریف (Sep 2023)
Investigation of the effect of elements in industrial wastes used in clay stabilization by geopolymer method
Abstract
Climate change and global warming pose significant threats to life on earth, leading governments worldwide to enact laws restricting carbon dioxide emissions. Traditionally, the use of Portland cement is a typical approach to increasing the bearing capacity, minimizing settlement, and improving seismic behavior of problematic soils. However, the cement industry's high energy consumption, uncontrollable emission of greenhouse gases, large carbon footprint, further depletion of natural resources, and high cost have become enormous challenges for all countries. Therefore, researchers continually seek new materials to replace ordinary Portland cement, contributing towards sustainable development. In this regard, the use of environmentally friendly, cheap, and readily available additives in modern soil methods of the construction cycle, particularly soil stabilization, is crucial. Geopolymer materials have recently emerged as serious alternatives to cement. This study aims to investigate the innovative reuse of eggshells through the geopolymerization process for engineering improvement of clayey soil. Alkali-activated binders are inorganic polymers that form repeated polymeric chains by polymerizing alumina and silica, sharing all oxygen atoms and using the alkaline cation. The combination of sodium hydroxide and sodium silicate was used as an alkaline activator in this study. The unconfined compressive strength (UCS) was the primary criterion for assessing the quality and effectiveness of the proposed solutions. This test was performed on selected combinations to assess the strength of the stabilized clay with different binder dosages and after different curing times. Moreover, the direct shear test was used to study the Mohr-Coulomb criteria parameters of the stabilized soil, namely the cohesion and angle of internal friction. Scanning Electron Microscope (SEM) microstructure observations of the natural and treated soil were conducted to investigate the strength development. The results showed that using 5, 7.5, 10, and 12.5% eggshell by dry weight activated by sodium hydroxide increases the UCS to 1.24 MPa, 1.21 MPa, 1.18 MPa, and 849 kPa, respectively, after 45 days of curing. The microstructural analysis results highlighted the reaction between the eggshell and the alkaline activator, resulting in the formation of an aluminosilicate gel.
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