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4 EOP System Installation and Field Testing

Below is a generic procedure for a typical floor installation of the EOP system as used by Drytronic of North America:

Below is a generic procedure for a typical wall installation of the EOP system as used by Drytronic of North America:

The first Army EOP demonstration was conducted at Fort Jackson, SC, during FY94. To advertise this demonstration, a sign was placed near the installation. Figure 7 shows Mr. Frank Cooper, Chief, Operations and Maintenance Division, Directorate of Public works Fort Jackson standing next to the sign.

Figure 7. Demonstration project sign.

On arrival at the site on 22 August 1994, the technicians from Drytronic (the company contracted for the installation of the EOP system) found that approximately one-third of the floor was covered with water, in some areas to a depth of 1 in. Before installing the EOP system, the larger cracks were waterproofed by chiseling out those areas above the water table where there were cracks and resealing those areas with hydraulic cement. For the EOP system, 83 rubber-graphite electrodes (anodes) were coated with a graphite-mortar mixture and inserted into holes drilled into all four walls, approximately 5 in. from the floor and 18 in. apart. Figure 8 shows a rubber-graphite anode. Twenty-four ft of rubber-graphite conductive cable was installed around the base of a concrete pad that supported steel water tanks in the room. Three copper grounding rods (cathodes) were driven into the exterior ground.

A Drytronic self-monitoring EOP Control Unit was mounted on one wall and all wiring from the anodes and cathodes was enclosed and wired into the unit. Additional work included patching holes in wall areas where equipment had been removed, and removing unneeded steel pipes and conduit. The control unit was activated on 26 August 1994.

Figure 8. Rubber graphite anode.

Figure 9 shows the basement mechanical room schematically, and highlights the locations of the EOP Control Unit, anodes, and cathodes. Figure 10 shows Mr. Cooper demonstrating the operation of the EOP control unit.

Figure 9. Layout of EOP installation at Fort Jackson.

Figure 10. Mr. Cooper demonstrating the operation of the EOP control unit.
EOP Control Unit Operating Data

The EOP power supply is configured to first generate a long duration positive direct current (DC) pulse between the anodes and cathodes followed by a much shorter negative pulse. The final pulse in the sequence is a zero voltage, or "rest," pulse. The pulse sequence and the individual pulse lengths are both programmable. Typical settings are 6 seconds for the pulse sequence, 4.8 seconds (or 80 percent of the sequence length) for the positive pulse, 0.3 seconds (or 5 percent of the sequence length) for the negative pulse, and 0.9 seconds (or 15 percent of the sequence length) for the rest period. Figure 3 shows an example EOP voltage waveform.

The EOP Control Unit power supply current load was within acceptable limits, varying from 0.75 Amps for a high humidity environment to less than 0.2 Amps for a low humidity environment. This is a result of the characteristics of the EOP system. The EOP power supply produces a voltage pulse of constant amplitude (i.e., a constant voltage power supply). The resistivity of the concrete is inversely proportional to the amount of water present in the concrete. As the water is slowly driven out, the resistivity of the concrete increases, dropping the current load of the power supply, since current is inversely proportional to resistance (Ohm's Law). Table 1 shows the current and voltage outputs of the EOP power supply. The slight increase in output current is due to the higher water table during July and August 1996.

During installation of the EOP system, concrete moisture readings were taken at different locations on the walls. The exact locations of these readings (and the locations of the three rebar specimens mentioned in the following section) are shown in Figure 11. Table 2 lists the moisture measurements taken at three different times: (1) at the time of installation, (2) at the 5-month performance check, and (3) 2 years after installation. The data are presented as percent relative humidity. All measurements were made at the concrete surface, not internally. The most suitable humidity for concrete structures is _70 percent. Note the direct correspondence between the power supply current (Table 1) and the concrete humidity (Table 2).

Table 1. DC power supply output.

Figure 11. Locations of moisture meters and rebar specimens in basement of Building 3265.

Table 2. Concrete moisture readings in Building 3265.

In addition to concrete moisture measurements, the corrosion of rebar specimens was investigated. Several small (~2-in. long) sections of 0.5-in. steel rebar were embedded in various locations in the walls of the basement at Fort Jackson. Table 3 lists the locations of these rebar specimens and Figure 11 shows the locations of three specimens.

Table 3. Location of rebar specimens.

Table 4. Specimen corrosion potentials.

The purpose of these specimens was to document whether any change occurs in the native corrosion potential of steel rebar that might be embed-ded in a concrete structure when the EOP system is operating. The corrosion potential of the specimens was tracked and compared to the average corrosion potential for reinforcing steel in concrete, which is approximately -0.2 VDC. Table 4 lists the corrosion potentials for some of the specimens. These potentials were taken at the 5-month performance check on 10 January 1995. The data show no significant difference in the corrosion potential from the native potential for the rebar specimens, however, these are just two time samples of a dynamic system. A larger record is needed to fully document the EOP system effect on rebar corrosion potential.

Monitoring Well

Another way to document the effectiveness of the EOP system is to track the groundwater table outside the basement wall. This is accomplished by using a monitoring well. The purpose of these measurements is simple: if the water table is above the floor of the basement and the basement remains dry, then the EOP system is fulfilling its purpose. Figure 9 shows the location of the monitoring well relative to the basement.

Each month, Davis & Floyd (the contractor responsible for monitoring the water table) reported the results of the water table data relative to the basement floor. Also recorded was the groundwater temperature. (Groundwater temperature was included in the standard monitoring well "package," it was not needed for this particular study.) Figure 12 shows the hydrograph from Davis & Floyd. The results for the monitoring well began in September 1995 and ended in September 1996. Note there are several times during the recording period when the water table exceeded the basement floor level, yet because of the EOP system the basement remained dry.

Rainfall data were taken monthly at Fort Jackson to track the months when there would be a greater potential for a higher water table. These data can be correlated to the monitoring well data points, as greater rainfall would result in a higher water table. (Specifically, note the correlation between the high rainfall during March 1996 and the rise in the water table during that month.) Table 5 shows the rainfall data at Fort Jackson up to May 1996.

Figure 12. Hydrograph line from monitoring well Fort Jackson.

Table 5. Average monthly precipitation data, Columbia, SC.

McAlester AAP

On 23 July 1996, installation began at McAlester. Figure 13 shows a layout of the basement in Building 5. During a walk-through of the building the previous day, standing water was seen in several areas of the basement. The locations of water infiltration were determined. These were in rooms A, B, and C. No intrusion was noted in the boiler room and under the stairwell, so the EOP system was not installed in these locations. In the unexcavated areas of the structure (crawl spaces), labeled "J" and "K" in the figure, it was noted that water had entered through a horizontal cold joint* approximately 2 ft from the top of the foundation walls. To prevent further water intrusion into these unexcavated areas, the cold joint was chiseled out and replaced with caulk.

The Drytronic technicians chiseled out an area of the concrete along the floor-wall juncture in the Industrial Hygiene Office (designated as "A" in the figure) where a horizontal crack was discovered. This area was patched over with new concrete. Concrete and soil resistivity tests were performed and the anode and cathode locations determined.
Figure 13. Basement of Building 5 at McAlester AAP.

Technicians then fastened a plastic wire mold onto the inside of the exterior concrete walls of the rooms where the EOP system was to be installed. These rooms are designated on Figure 13 as "A" (Industrial Hygiene Office), "B" (Medical Supply Storage Room), and "C" (Electrical Room). This wire mold was mounted 5 in. above the floor and conceals the anodes and system wiring. Junction boxes were placed every 15 ft along the wire mold. Holes were then drilled through this wire mold and into the concrete walls. These holes, to accommodate the anodes, were drilled 6 in. into the concrete walls, 5 in. above the floor and 11 in. on center. The total number of anodes is 95 and the number of anodes for each wall is: 20, 15, 24, 9, 19, and 8, respectively, starting with the east wall in room A, and moving clockwise around the basement. Rubber-graphite anodes were coated with a graphite-mortar mixture and inserted into the holes. The anodes were wired in segments of about 20 anodes. The segments were then connected in a parallel and redundant manner (connected at both ends) to the power supply. All wiring was enclosed in the wire mold.

Copper-clad steel grounding rods (cathodes), 8 ft long, were driven into the ground in selected areas. This project required five cathodes and they were placed as indicated in Figure 13. Wiring from the cathodes was installed and placed in the wire mold. To differentiate the wires, blue wire connected the anodes and black the cathodes. The covering for the wire mold was then secured in place.

Drytronic technicians drilled holes at several places in the basement walls for sensors: holes were drilled perpendicular to the wall surface in three different locations to accommodate 6-in. long rebar specimens; a horizontal groove measuring 16 in. long by 1.5 in. deep was chiseled 8 in. above the floor into the south wall of the Industrial Hygiene Office to hold a long steel rebar specimen; a hole was drilled at a 45 degree angle downward into the wall behind this groove for a corrosion reference cell; and finally a hole was drilled in the south wall near the southeast corner of the Industrial Hygiene Office to accommodate a temperature and humidity sensor. The rebar specimens were used by CERL to monitor rebar corrosion potential and the temperature and humidity probe was used to monitor moisture in the concrete wall. Finally, the EOP Control Unit was mounted on the north wall of the electrical room (labeled "C" in Figure 13). The relative humidity in the Industrial Hygiene Office was 70 percent at this time. The installation portion of this project was completed on 31 July 1996.

The EOP waveform was recorded by an oscilloscope on several occasions. The oscilloscope provides a real-time picture of the waveform and shows the maximum, average, and minimum voltage values and the point at which the voltage goes to zero. Figure 14 shows a waveform taken from the EOP unit at McAlester AAP, November 1996. The normal operating voltage range, peak to peak, is _60 Volts DC (VDC). The positive voltage peak was _30 VDC. During the positive pulse, the water is forced in the direction of the cathode or to the exterior surface of the concrete.

Many of the same parameters that were recorded at Fort Jackson are being recorded at McAlester. The corrosion potential is taken using a 13-in. long piece of 0.5-in. steel rebar that was grouted into the wall along with a Ag/AgCl reference cell. The cell was installed so as to be behind the rebar, and separated from it by about 2 in. of concrete. The humidity of the concrete is sampled, but not with the same technique used at Fort Jackson. A small cavity (approximately 6-in. long) was made in the concrete wall for the insertion of a 4-in. long dual humidity/temperature probe. After the probe was inserted into the cavity, the cavity was sealed off from the room air. Since the cavity is sealed, this probe monitors the temperature and humidity of the cavity, giving an indication of the progress of the EOP system as it operates. The humidity of the cavity should be proportional to the moisture content of the concrete.

Ambient room humidity and temperature sensors are monitoring the Industrial Hygiene Office. A well was installed to monitor the level of the water table outside the basement. In addition to these sensors and probes, the electrical power consumption of the EOP system is monitored to determine the power output of the power supply and the cost of operation. Most of these monitoring devices are fed into a datalogger that is installed on site and is remotely accessible via modem. The data is collected and stored in the datalogger until downloaded to a computer.

The parameters being remotely monitored in Building 5 are:

The EOP control Unit DC output power is being computed from the AC input power and the known power consumption of the unit's control electronics.

Rebar potentials are being sampled about every 4 months. Unfortunately they could not be sampled remotely; they must be measured on site.

The daily rainfall, average outdoor temperature, and average outdoor relative humidity at McAlester are obtained from the Oklahoma Climatological Survey (Data is downloaded monthly from their INTERNET site). Sample data are included in the Appendix to this report.

Figure 15 shows some of the recorded data, and highlights the power consumption of the EOP system in relation to the relative humidity in the wall, as measured by the wall probe. Figure 15 shows that, initially, as the power consumption drops (as a result of the decrease in current as the water is driven out), the concrete humidity drops as well. This shows that the EOP system is decreasing the moisture content in the concrete and is decreasing its power requirements, both excellent indicators that the system is working properly. Figure 16 shows the water table with respect to the basement floor. (Figure 16 gives the same information for McAlester that Figure 12 gives for Fort Jackson.) Unlike the conditions recorded at Fort Jackson the water table at McAlester AAP does not rise above the basement floor. Therefore the water intrusion problem at McAlester is due entirely to periodic saturation of the nearby soil. This conclusion is further supported by the building's occupants, who stated that the water came in following rainstorms.

Figure 15. Power consumption of EOP system in relation to relative humidity in the wall.

Figure 16. Water table with respect to the basement floor for McAlester AAP.

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