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The Theory
Swelling clays have the potential for volume change during changes in moisture content. The volume change potential of swelling clays can be significantly reduced by the application of EcSS3000. Treatment with this product uses physio-chemical soil principles to change the swell/shrink characteristics of the clay soils. Smectite clays exhibit high swell/shrink potential due to the very high surface area of the clay particles and the development of negative charges in the clay particle and on the clay particle surface due to isomorphous substitution in the clay lattice structure. Isomorphous substitution of Al for Si in the silicate (tetrahedral) sheets and Ca and Mg for Al in the gibbsite (octahedral) sheets generates a net negative charge on the lattice layers which is compensated by interlayer cations. To preserve electrical neutrality, exchangeable cations and polarized water molecules are attracted around the surfaces of the negatively charged clay particles. The combination of exchangeable cations and polarized water molecules form a layer around the clay particle called the diffuse double layer. The expansion or collapse of the diffuse double layer will determine whether the clay soil has a higher or lower potential for swell.
The following Figure presents a generalized depiction of the Montmorillonite (smectite) clay particle structure:
Structure of Expansive Montmorillonite Clay
The application of the very diluted EcSS 3000 chemical collapses the diffuse double layer through the process of cation substitution in the clay lattice structure and cation exchange in the diffuse double layer adjacent to the negatively charged surface of the clay particle. These processes plus the increase in the cation density adjacent to the clay surface particles will collapse the diffuse double layer which in turn reduces the repulsive forces between adjacent clay particles and increases the attractive forces between the clay particles. The end effect will be a tendency for the clay soil particle structure to transform from a dispersed clay structure with a higher potential for swell to a flocculent structure with less potential for swell.
There has been extensive research performed on EcSS 3000 at Texas A&M University and Penn State University. This research is presented in the Resources Section of this WEB Site. A summary of the results of some of the research is presented as follows:
- Letter Report from Dr. R. Malek, Director, Particle Characterization Laboratory, Materials Research Institute, Pennsylvania State University, University Park, PA 16802, “Effect of EcSS 3000TM on Expansive Clays”, November 9, 2004.
- EcSS 3000TM increases ionic strength in the local area of injection, which results in:
- Drawing water from other area through osmosis. However, this water remains free (mobile), i.e. not migrating into the interlamellar spaces.
- Depressing the thickness of the double layer providing less water for exchange with the interlamellar spaces in the clay.
- The soluble species in EcSS 3000TM adsorb on the surface of the clay generating an electrosteric effect. In addition, a hydrophobic environment is created at the surface of the particle which tends to repel water.
- There is a trend towards a change from high Al occupancy to low Al occupancy in the silicate sheets, resulting in structural changes in the expansive clay:
- decrease in the negative charge (evidence: zeta potential), and
- destabilizing the silicate structure.
- Sarkar, Shondeep L., Herbert, Bruce E., and Scharlin, Russell J., August 5, 2000, “Injection Stabilization of Expansive Clays Using a Hydrogen Ion Exchange Chemical”, ASCE, Advances in Unsaturated Geotechnics.
- Identifiable smectite peaks were noted to be absent in the Hydrogen Ion Exchange Chemical – treated coarse and fine factions.
- The treatment of clay samples reduced the Zeta potential of the treated sample by 32 % as compared with the untreated clay sample. The Zeta potential is a measure of the negative charge in the clay and on the clay surface. As the Zeta potential decreases it is considered that the double diffuse layer is also reducing.
- Soluble ions analysis of Al and Fe supports the hypothesis that the Hydrogen Ion Exchange Chemical treatment changes the surface chemistry of clays through a complex precipitation-dissolution process; the low pH may be a contributory factor. The treatment of the clay with the Hydrogen Ion Exchange Chemical reduced the soluble Al ions by 43 % and increased the soluble Fe ions by 173 %.
- The Environmental Scanning Electron Microscope examination showed that no morphological changes occur when clay sample is treated with the Hydrogen Ion Exchange Chemical solution, but swelling becomes evident in the counterpart water-treated sample.
- The Transmission Electron Microscope examination revealed that the crystalline electron diffraction pattern of smectite in the treated sample is replaced by diffuse halos, implying a change in the clay structure or a smearing of the smectite particles by an amorphous or non-crystalline material.
- During sample handling and processing, the treated sample was continually recognized as having different behavior compared to the untreated sample. The untreated sample was more “stickier”, as opposed to the treated sample that was much more difficult to disperse.
- The dominant conclusion of this study is that soil samples amended with the Hydrogen Ion Exchange Chemical solution exhibit a change in the crystallographic characteristics of the soil, which can be associated with a change in the shrink-swell behavior of smectite.
- Letter Report from Sarkar and Associates, Inc., Texas Transportation Institute, to Environmental Soil Stabilization Ltd., “Magic Angle NMR Study of ESSL – treated Bentonite, September 23, 2002.
- The results of the Si magic single spinning nuclear magnetic resonance spectroscopy shows the loss of Al in the tetrahedral sheets for clays treated with the EcSS 3000. The loss of Al tetrahedral indicates a disintegration of the aluminosilicate sheets. Additionally; there appears a new peak at a chemical shift of -76 ppm corresponding to the terminal groups of the aluminosilicates sheets. The appearance of this peak indicates a breakdown of the large aluminosilicate sheets into smaller units.
- Letter Report from Dr. R. Malek, Director, Particle Characterization Laboratory, Materials Research Institute, Pennsylvania State University, University Park, PA 16802, April 11, 2005.
- The EcSS 3000 soil stabilizer is leaching or substituting the Al atoms out of the tetrahedral lattice layers which reduces the clay particle negative charge which in turn stabilizes the soil. This process is irreversible as introducing the Al atoms back requires exposure of the soil to the lengthy alterations process under drastic conditions of temperature and pressure that are not found in naturally exposed soils.
The following Figure was developed by the manufacturer of EcSS 3000 to depict the electrochemical reactions occurring when EcSS 3000 is applied to a swelling clay soil:
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