Low plasticity clay stabilized with cement and zeolite: An experimental and environmental impact study

Abstract

To mitigate environmental issues caused by conventional binders and gain superior geotechnical properties, pozzolanic materials can be considered for soil stabilization purposes. Herein, the effectiveness of zeolite for enhanced treatment of cement-stabilized clay was studied by measuring pH, maximum dry unit weight (MDUW), optimum moisture content (OMC), unconfined compressive strength (UCS), and accumulated loss of mass (ALM), as well as carrying out scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses. Then, the life cycle assessment (LCA) analyses were conducted to evaluate the potential environmental impacts of cement and zeolite production and their use as stabilizing agents in clayey soil. The soil was stabilized by 2, 4, 6, and 8% cement contents and 0, 15, 30, 45 and 60% cement replacements with zeolite. Furthermore, 56-day curing time was considered to assure accomplishment of hydration and pozzolanic reactions. Besides, samples were exposed to up to 8 wetting-drying cycles to evaluate durability-based parameters. The environmental impacts of the combination of cement, zeolite, and clay for constructing a one-kilometer pavement subgrade in terms of greenhouse gas (GHG) emissions and energy consumption in production, transportation, and execution were studied using LCA. Finally, Al2O3, SiO2, and CaO components were discussed to react with one another and to participate in the chemical reactions as the active composition (AC). UCS results indicated that up to 15% cement content replacement with zeolite, strength increased whereas it reduced thereafter. UCS and ALM were observed to decrease and increase during wetting-drying cycles, respectively. The efficacy of optimum zeolite percentage was more noticeable in higher cement percentages, both in terms of mechanical and durability tests. LCA confirmed that the efficiency of energy consumption and GHG emissions reduced with increasing zeolite. Also, for the samples containing zeolite and cement, the porosity parameter (n)/AC was nominated as a key controlling parameter for determining the UCS, ALM, consumed energy, and the produced CO2. Regarding the experimental program and LCA, the use of zeolite instead of cement is highly recommended both in terms of moisture changes, mechanical properties and environmental aspects.