Masters Theses

Date of Award

8-2013

Degree Type

Thesis

Degree Name

Master of Science

Major

Civil Engineering

Major Professor

Angelica M. Palomino

Committee Members

Khalid Alshibli, James A. Mason

Abstract

There are many different types of clay that exist throughout the world, and many are characterized by undesirable engineering properties. Soil improvement techniques are often implemented on these soils such as solidification, reinforcement, etc. However, these solutions are a “static” approach, as the soil’s properties cannot be modified over time. The development of the specific clay-polymer composites used in this study was motivated by the idea of creating a geomaterial that could be modified over time by adjusting its fabric, namely in the form of controlling interparticle and interlayer spacings. Therefore, the composites that are used in this study are “responsive” to changes in the external environment, which has been proven at the micro-scale in previous studies.

Tests were performed on these clay-polymer composites using two different types of clay, kaolinite and montmorillonite, in order to determine their shear strength and compressibility parameters, as well as their shear wave velocities, and to determine any links between their observed meso-scale behavior and known micro-scale behavior. It was shown that with the addition of polyacrylamide (PAM) polymers, which are sensitive to pH and ionic concentration variations, the normalized shear stress was increased when compared to the control samples under the same conditions. However, no link was found between the known polymer conformation of PAM and the clay-polymer composites’ normalized shear stresses.

The compressibility, Cc [compression index], and Cr [recompression index] values of the clay-polymer composites were also shown to be higher than in the control samples. Shear wave velocities, however, were shown to have no significant correlation to the sample type or test conditions, indicating this testing may not be a useful method of distinguishing between the stiffness of control and composite samples. Finally, “tunability” was shown for kaolinite-PAM samples. PAM’s extended conformation at high pH and low ionic concentration led to greater increases in compressibility, greater decreases in Cv [coefficient of consolidation], greater increases in Cc, and greater increases in Cr. Thus, an extended polymer conformation was determined to be more compressible and can exhibit greater changes in its behavior than a coiled polymer conformation.

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