Impact of cyclic freezing and thawing on the pozzolanic consolidation of heavy metal contaminated soils

Authors
F. Khosravi 1
S. Hamidi 2
S. M. Marandi 3
1 Department of Civil Engineering, Faculty of Civil Engineering, Shahrood University of Technology, Semnan, Iran.
2 PhD Candidate of Civil Engineering, Faculty of Civil Engineering, Shahid Bahonar University of Kerman, Kerman, Iran.
3 Professor of Civil Engineering, Faculty of Civil Engineering, Shahid Bahonar University of Kerman, Kerman, Iran.
Abstract
Heavy metals are elements that exhibit metallic properties such as ductility, malleability, conductivity, cation stability, and ligand specificity. They are characterized by relatively high density and high relative atomic weight with an atomic number greater than 20. Clay and other soils may become contaminated by the accumulation of heavy metals and metalloids through emissions from the rapidly expanding industrial areas, mine tailings, disposal of high metal wastes, leaded gasoline and paints, land application of fertilizers, animal manures, sewage sludge, pesticides, wastewater irrigation, coal combustion residues, spillage of petrochemicals, and atmospheric deposition. Heavy metal contaminants in addition to geotechnical problems creation and change in the soil strength parameters especially in clay soils, can cause environmental and human health risks due to penetrate through the groundwater. Most commonly heavy metal found at contaminated sites are lead (Pb), chromium (Cr), arsenic (As), zinc (Zn), cadmium (Cd), copper (Cu), mercury (Hg), and nickel (Ni). Also, freezing and thawing cycles have a significant effects on the behavior of stabilized clay soils specially on the heavy metal contaminated clay soils stabilized by cement od other additives. So, by population increasing, advancement of technology and consequently increase in heavy metals emissions, as well as being a quarter of the earth surface in the cold regions and the necessity of building design and construction on these soils, it seems necessary to study the impact of the freezing and thawing cycles on the stabilized clay soils. Different additives such as cement, lime, gypsum, fly ash and other additives were used for stabilization and solidification of heavy metal and oily contaminated soils, the cement is more practical among the stabilizer additives, because of its compatibility with pollutants and high efficiency, low cost and easy access. In this research used cement for stabilization of the lead heavy metal contaminated soil exposed to freezing and thawing cycles. According to the importance of the soil settlement in the clay soils, one dimensional consolidation test was conducted on the experimental samples. Also, due to extensive use of bentonite clay soil in contaminated sites, bentonite clay sample was used for experimental studies. The results of this research indicate that in most cases the critical cycle is a cycle 7. Also, The soil strength parameters such as over-consolidation stress increased about 2 to 8 times in different conditions by cement stabilization. Also, stabilization of heavy metal contaminated by cement clay soils that exposed to freezing and thawing cycles reduce the Cc and Cs coefficients of bentonite clay samples about 50 to 80 percent depending on number of freezing and thawing cycles and heavy metal concentration in bentonite clay sample and also causing preconsolidation in soft clay soils or normally consolidated soils throug the pozzolanic reactions of soil and cement at a low time. Furthermore, the optimum content of cement in contaminated and uncontaminated samples in different freezing and thawing cycles is variable, but in most cases is about 5% to 10% depending on number of freezing and thawing cycles and heavy metal concentration in bentonite clay sample. In continence, stabilization efficacy and the formation of hydrated compounds of cement and clay soil was investigated by using pH chemical test.

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Modares Civil Engineering journal
Volume 18, Issue 2
July and August 2018
Pages 75-87