Abstract

Improvements in the strength and durability of frost-susceptible soils and aggregates can be achieved through chemical stabilization using portland cement, where the efficacy of cement stabilization for improving durability depends on the degree to which hydraulic conductivity is reduced. Hydraulic conductivity is commonly estimated from basic soil properties using Moulton's empirical equation. However, the hydraulic conductivity estimation does not consider the detrimental effects of freezing or the benefits of cement stabilization. The purpose of this research was to derive new equations relating hydraulic conductivity after freezing to specific material properties of cement-treated soils and aggregates stabilized with different concentrations of cement. This research included material samples from two locations in Alaska and from single locations in Minnesota, Montana, Texas, and Utah, for a total of six material samples. Each soil or aggregate type was subjected to material characterization by the Unified Soil Classification System (USCS) and the American Association of State Highway and Transportation Officials (AASHTO) classification system. Moisture-density curves were developed, and unconfined compressive strength (UCS) testing was performed to determine cement concentrations generally corresponding to low, medium, and high 7-day UCS values of 200, 400, and 600 psi, respectively. After being cured for 28 days at 100 percent relative humidity, the prepared specimens were subjected to frost conditioning and hydraulic conductivity testing. The Alaska-Elliott, Minnesota, Montana, and Utah materials exhibit decreasing hydraulic conductivity with increasing UCS, the Texas material exhibits increasing hydraulic conductivity with increasing strength from the low to medium cement concentration levels but decreasing hydraulic conductivity from the medium to high cement concentration levels, and the Alaska-Dalton material exhibits increasing hydraulic conductivity with increasing strength. Multivariable regression analyses were performed to investigate relationships between hydraulic conductivity and several material properties, including soil gradation and classification, fineness modulus, specific gravity, cement content, porosity, compaction method, dry density, and 7-day UCS for each specimen. The R2 values computed for the six-parameter, four-parameter, USCS, and AASHTO-classification models are 0.795, 0.767, 0.930, and 0.782, respectively. Further research is recommended to investigate the effects of cement on hydraulic conductivity for USCS and AASHTO soil types not covered in this research.

Degree

College and Department

Ira A. Fulton College of Engineering and Technology; Civil and Environmental Engineering

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