Electro-osmosis
What is "Electro-Osmosis" ?
When electrodes are placed across a clay mass and a direct current is applied, water in the clay pore space is transported to the cathodically charged electrode by electro-osmosis. Electro-osmotic transport of water through a clay is a result of diffuse double layer cations in the clay pores being attracted to a negatively charged electrode or cathode. As these cations move toward the cathode, they bring with them water molecules that clump around the cations as a consequen ce of their dipolar nature. In addition, the frictional drag of these molecules as they move through the clay pores help transport additional water to the cathode. The macroscopic effect is a reduction of water content at the anode and an increase in wate r content of the clay at the cathode. In particular, free water appears at the interface between the clay and the cathode surface. This excess of free water at the cathode has lubricating effects.
The original electro-osmotic experiments showed that flow of water through a clay-water system (with the applying of an electric field to the soil) is initiated by the movement of cations that are closely attrac ted to the surface of the clay particles. Electro osmosis is possible in clay soils since clay minerals have a net negative charge. As a result of this charge, a gradient in electrical potential forms (O that extends into the water surrounding the particl e. Cations are attracted to the surface of clay particles when the soil is hydrated to balance the negative potential.
The cations that are attracted to the surface of the particle can be separated into two regions. The first region consists of cations, which are held tightly to the particle. This region is called the Stern layer. The second layer is the diffuse layer, where a layer of attracted but mobile cations extends into the surrounding liquid. These cations are attracted to the surface by the electrical potential but contumely move away from the particle because of thermal f luctuations. The concentration of cations in the double layer diminishes as the distance from the surface of the particle increases. Ultimately, the double layer blends into free water.
Electro-osmosis occurs in clay soils when cations in the double layer are driven by the application of an electrical field, and as a result, a velocity field in the pore fluid develops, as shown in Figure 1. The ve locity distribution changes rapidly near the particle's surface, but then becomes flat at the edge of the double layer. Therefore, electro-osmotic flow appears as plug flow through the pores of soil.
The cations that are attracted to the surface of the particle can be separated into two regions. The first region consists of cations, which are held tightly to the particle. This region is called the Stern layer. The second layer is the diffuse layer, where a layer of attracted but mobile cations extends into the surrounding liquid. These cations are attracted to the surface by the electrical potential but contumely move away from the particle because of thermal f luctuations. The concentration of cations in the double layer diminishes as the distance from the surface of the particle increases. Ultimately, the double layer blends into free water.
Electro-osmosis occurs in clay soils when cations in the double layer are driven by the application of an electrical field, and as a result, a velocity field in the pore fluid develops, as shown in Figure 1. The ve locity distribution changes rapidly near the particle's surface, but then becomes flat at the edge of the double layer. Therefore, electro-osmotic flow appears as plug flow through the pores of soil.
Water Intrusion Technologies has an advanced solution for removing and keeping water out of subterranean concrete walls and slabs, which is Electro-Osmotic Pulse (EOP) technology. Traditional methods for correcting water intrusion involved the application of sealants or costly excavation around a facility exterior. In 1994, a team of researchers and the U.S. Army Engineer Research and Development Center (ERDC) began development of an innovative technology for the prevention of water intrusion in below-grade concrete structures. This technology has been successfully used in basements, elevator shafts, tunnels, underground bunkers, crawl spaces and recently a roadway. The heart of this technology is strategically placing an Anode (titanium strip) on the dry side and Cathode (copper rods) on the wet side and passing a controlled current from the Anode to the Cathode. Water attaches to the electrically charged ions as they move from the Anode to the Cathode and therefore the water is removed from the controlled media. One of the many challenges was keeping the rebar, which is embedded in the concrete for strength, from corroding. A high tech controller, patent pending, was designed to provide controlled current flow through the concrete and protecting the rebar while managing multiple zones.
A multimillion dollar project using this technology was just completed in Santa Barbara California. A Soggy Problem was the headlines in the Santa Barbara News-Press on August 20, 2006. A highway off ramp and underpass has been the site of many vehicle accidents costing California millions in lawsuits. A solution for the soggy problem had stumped public works officials for decades. This underpass handles over 20,000 vehicles a day. The paper went on to say, a fix would do more than dry out the over 70,000 square feet of roadway. Success would allow Caltrans to put off a $20 million to $30 million replacement of the interchange scheduled for 2012. Caltrans did find a fix. They found out about Electro-Osmosis Pulse Water Removal. This was a challenging project because of the square footage involved and the concrete with reinforcement steel. OsmoTech did the installation over scene by the U.S. Army Corp of Engineers. DSP Automation developed a new controller for this application to power the anodes and protect the reinforcement steel. The system covered the 70,000 square feet of roadway and consisted of 35,000 linear feet of anode. Within five days of turning on the system, a once very wet roadway was dry.
We are currently involved in waterproofing underground bunkers. This has also been a major problem for years. There are over 40,000 bunkers with moisture seeping through the concrete walls and floors causing high humidity, mold and corrosion. This is a very costly environment for equipment and humans. No other technology has successfully kept the water out for any reasonable length of time.
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