Assessing the Quality of Soils Modified with Lime Kiln Dust

Abstract

By-product materials such as lime kiln dust (LKD), cement kiln dust, and fly ash are used for modifying pavement subgrades. It is insufficient to use density and water content measurements for compaction quality control on modified soils where chemical reactions occur because the properties of the modified soil differ from those of the parent materials. The amount of lime, the clay mineralogy, the soil water content, and the percentage fines in the soil are important parameters that affect the compaction behavior and subsequent properties of the modified soil. Hence, they should be considered for effective quality control. The behavior of soils modified with LKD is more complex than that of soils modified with lime because of the presence of various compounds besides lime in LKD. Research indicates that the electrical conductivity of soil is strongly affected by chemically modifying soils and tracks the chemical reactions with time. Time domain reflectometry (TDR) technology using the Purdue TDR apparatus measures the electrical conductivity of soil and is feasible for use in the laboratory and in the field. This paper describes the electrical conductivity behavior of an LKD-modified soil for various compaction conditions. The variation of electrical conductivity with time for a given cohesive soil is shown to depend on the amount and type of LKD and the water content. A hyperbolic-type model is proposed to capture the change in electrical conductivity with time for different amounts of LKD. Test results indicate that electrical conductivity also can be correlated to the penetration resistance of modified soil, which is an indicator of shear strength. Compared with conventional test methods, TDR is expected to provide better understanding of the rate and extent of chemical reactions between chemical modifiers such as LKD and soil and be useful for compaction quality control.

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