This paper is focused on chemical diffusion parameters of soil-bentonite mixture which is one of barrier materials commonly used for containment of ground contamination. Although vertical cutoff ...walls using low-permeable materials, such as soil-bentonite mixture, need to prevent mobile contaminants from migrating in the aquifer for a long period, a limited number of studies have focused on chemical diffusion through hydraulic barriers, whereas factors affecting hydraulic conductivity of barrier materials have been frequently discussed. In this study, solute transport through soil-bentonite mixtures made with a bentonite powder content of 50 kg/m3 was evaluated by a laboratory experiment using an acrylic vertical column and a one-dimensional advection-dispersion finite element analysis. Two soils having different particle size distributions were used as parent soil. By fitting experimental and numerical results regarding the chloride flux, effective diffusion coefficient, De, and effective porosity, ne, of the mixtures were determined with two significant digits. Results obtained in this study indicate that soil-bentonite mixtures made with a same bentonite powder content can have a similar De value, regardless of the type of parent soil. Another important finding is that larger total porosity of mixtures led to smaller ne value probably because powder bentonite can sufficiently hydrate and swell in macropores of the mixture with a larger total porosity; therefore, pore structure of bentonite became more dominant for that of soil-bentonite mixture.
Development of low-cost and environmentally-friendly techniques to treat construction wastes containing toxic substances is one of the crucial issues in construction projects. A mechano-chemical ...treatment technology for construction waste containing non-scattering asbestos, such as cement-asbestos slate boards, has been developed recently. This treatment process discharges high water content sludge, which is composed of fine-grained waste slate, as a residue, since slate boards are crushed and ground into fine particles under a wet condition to enhance the reactivity between a treatment agent and asbestos. Recycling this high water content residual sludge is a challenging issue to improve the environmental suitability of this treatment technology. In this study, applicability of two cement treatment techniques (i.e. granulation and liquefied stabilization) was investigated for recycling this sludge in geotechnical applications. Granulated sludge was accepted for geotechnical utilization in regards to its mechanical properties. For liquefied stabilization, workability, bleeding, unconfined compression strength and consolidation characteristics were evaluated for the sludge treated with various water-cement (W/C) ratios. Testing results indicated that these characteristics of the liquefied stabilized sludge were consistent with those of typical high water content cement-stabilized soil, and W/C is a fundamental parameter for the compressive strength.
Soils excavated in construction works often contain non-anthropogenic heavy metals and metalloids due to their geologic histories. Evaluation of their leaching behaviors is essential to predict the ...environmental impact and achieve an optimum design when reusing such soils as construction materials. However, applicability of the conventional column leaching test to soils containing non-anthropogenic substances is uncertain, since their chemical forms and leaching processes are different from those in contaminated soils. Also, the column size is one of factors influential to the leaching behavior. This paper addresses the leaching behaviors of arsenic (As) and other inorganic constituents contained in a marine sediment by employing two different-size column percolation tests (50 mm in diameter × 300 mm in height and 150 mm in diameter × 700 mm in height) with saturated/unsaturated flow conditions. Long term leaching profiles were analyzed to assess the effects of specimen size and flow conditions. At the middle of the unsaturated larger column, higher As leaching concentrations were observed under neutral condition. However, As leaching was limited at the bottom due to precipitation of As with co-precipitation of iron and aluminum compounds. As a result, there was no significant difference in both As leaching amount and leaching processes obtained in two column percolation tests.
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