How is EOP Used to Waterproof Foundations?
Electro-osmotic pulse (EOP) is a method that is being used more frequently for both new construction and repair work when waterproofing concrete. But what is it exactly?
EOP is used for waterproofing in a very similar way cathodic protection is used for corrosion prevention in structural steel reinforcement. An EOP protection system has an anode and cathode and a flow of electricity between them create an electric field within the concrete. The anode is of mixed metal oxide titanium and attached to the concrete.
A coppercoated steel rod cathode is driven into the soil backfill region outside, but near the wall. A small DC-pulsing current passes between the anode and the cathode and moves moisture to the outside face of the wall. When concrete is moist or wet, it is very conductive and more electricity is used. When concrete is dry, very little electricity is consumed.How does it work?
So, how does this system work in application? In moist concrete, there are molecules of calcium cations, hydroxyl anions, and of calcium hydroxide (Ca(OH)2). These molecules are forming and splitting apart all the time. When electricity flows through moist concrete, it causes calcium cations to slowly move in the direction of the cathode toward the outside of the wall. Hydroxyl anions slowly move in the direction of the anode on the inside face of the wall. This activity occurs in the pores and canal structures of the concrete, which is also where moisture can be found.
The cations move to the outside face of the wall in solution with water where they concentrate in the micro pores. Because concrete is a semipermeable membrane, by osmosis water is attracted to the calcium cations, thus creating osmotic pressure. The resulting effect is that the relative humidity (RH) toward the inside of the concrete wall is lowered while the RH at the outside concrete regions is raised. When an EOP protection system is engaged for a period of time, the outside wall RH approaches 100% while the RH on the inside of the wall can become as low as 45%.
The goal is for the hydrostatic pore pressure in the outside region of the concrete to be higher than the hydrostatic pressure of wet soil against the wall. In a properly balanced EOP system, this happens: water flows through the concrete in one direction with osmotic pressures as high as 20 to 30 psi, which is much higher than soil hydrostatic pressure associated with residential construction (no higher than 4 psi). The anions have no real effect on the process, except to offer some protection to reinforcing steel due to the higher alkalinity.What are the benefits to using EOP?
For concrete applications, EOP technology significantly outperforms conventional technology. EOP offers a long-term, cost-effective alternative to the trench-and-drain approach to mitigate water-related problems. System installation is quick (typically about 1 week). The EOP system is installed from the interior (negative side) of affected areas, avoiding the cost of excavation and interruptions to normal operations.
The use of EOP technology can eliminate corrosion damage to mechanical equipment and improve indoor air quality by maintaining the relative humidity on the interior wall and floor surface to prevent mold and bacteria growth. This technology can also prevent mineral deposits (efflorescence) and eliminate rising damp in walls.Where is the best application of EOP protection?
The best markets for EOP protection are probably high-end residential and commercial construction, where perimeter excavation cannot be performed and interior drainage is not acceptable.