Interface Modeling for Electro-Osmosis in Subgrade Structures

Abstract : Conventional waterproofing techniques for below grade structures are ineffective, expensive and short lived. Electro-Osmotic Pulse technology is an alternative technique to controlling moisture movement in porous medium. A research study was undertaken to model the complex osmotic behavior of a system consisting of portland cement with aggregate and different clays (kaolinite. montmorillonite, limestone and quartz sands) created to simulate below grade structures. A direct current 30- to 45-Volt source was applied across the 8- inch cell of concrete and backfill. The electrolytes used were sodium chloride and calcium chloride. The results showed the electromigration of a low pH front interacted with the high pH present in the concrete matrix to form complex calcium precipitates (CaCO3) that fill the pore space and microcracks along the path of osmotic flow. As the experiment continued, the osmotic flow reduced as the pore voids continued to fill with water insoluble precipitate.