Family of Compaction Curves for Chemically Modified Soils

Abstract

Lime and Lime Kiln Dust (LKD) are widely used for modifying/stabilizing pavement subgrades. The addition of lime or LKD involves chemical processes that are dependent on many parameters. For natural subgrades, quality control is based on moisture and unit weight requirements using manual interpolations of one-point test data on a family of curves. For modified soils, moisture and unit weight measurements are insufficient for quality control and other tests must be considered. Various possible quality control methods for LKD-modified subgrades were evaluated. This research produced an Excel-based program to automate the generation of a family of curves and one-point data interpolation. Families of curves for LKD-modified soils did not vary systematically, limiting their usefulness in quality control. Dynamic cone penetrometer (DCP) and Time domain reflectometry (TDR) tests were considered as alternative means to achieve field quality control. The DCP test although promising, requires supplementary tests for completely characterizing a modified subgrade. LKD modification of soil involves chemical reactions which can be indirectly studied by measuring the electrical properties. The dielectric constant and electrical conductivity of a LKD-modified soil were measured using the Purdue TDR apparatus. Preliminary test results show that with the knowledge of two calibration constants, the dielectric constant of a soil measured following the Two-Step TDR test (ASTM D 6780) can be used for water content and unit weight determinations. The electrical conductivity of a LKD-modified soil decreases with time in a manner that is similar to the one-dimensional consolidation of a soil. The variation in electrical conductivity with time of a LKD-modified project soil was correlated to its strength and was also used to estimate the amount of LKD present in the soil. Future research should focus on extending these observations to other soils and to formulating a protocol for using the TDR test along with the DCP test for quality control of LKD-modified soils.