Comparison of soil physical and chemical properties in salt-affected soil amelioration with desulfurization gypsum and waste concrete in China

抄録

In countries with arid and semiarid regions, decrease in agricultural production due to excessive salts is a very serious problem. In China, because environmental problems due to air pollution have caused much damage to the ecosystem and humans, the new usage with the increase in the desulfurization gypsum is required recently. Moreover, the accelerating urbanization has generated a huge amount of construction and demolition wastes. Therefore, the need for the recycling and reuse of both desulfurization waste and waste concrete is very urgent and necessary. In this study, the physicochemical amelioration effects in the salt-affected soil with desulfurization gypsum, cement fine powder (CFP) and waste concrete (WC) were reported. Sodic soil in Yinchuan, China was used in amelioration test. Waste cement fine powders (CFP) (≦200 µm), waste concrete particles (WCP) (≦0.6 mm, 0.6-1.0 mm, 1.0-2.0 mm and 2.0-4.75 mm) were examined as soil amendment. The CFP and various WCPs based on both 0.5wt% application rate of wet FGD gypsum (W-FGDG) and 1.0wt% application rate of semi-dry FGD gypsum (SD-FGDG) were added to soil. Soil properties (pH, EC, exchangeable Na, soluble ions (Na, Ca, Mg and K)) before and after mixing with soil amendments were measured. Consequently, the order of Ca concentration that is effective for sodic soil amelioration was SD-FGDG>W-FGDG>WCP>CFP. All sodic soils decreased drastically in EC and ESP, and soil pH decreased gradually after three and six weeks. Consequently, the smaller WCP could ameliorate at a smaller amount of application rate. In addition, we investigated the change of hydraulic conductivity and the solute transport in soil amelioration. In order to analyze the solute transport due to soil amelioration, soil column equipped with tensiometers and four-electrode sensors has been used. Consequently, the initial Na leaching was confirmed from the results of EC of leachate and quantitative analysis of leachate. And the increase in hydraulic conductivity due to waste concrete application could be confirmed. These results indicated the effectiveness of waste concrete as salt-affected soil amendments in China.