Chapter 1
INTRODUCTION
1.1 General Groundwater intrusion through a building's foundation can cause serious damage. In addition to increased concrete deterioration and accelerated rebar corrosion, basement dampness can ruin expensive electrical and mechanical equipments, which are often located in basement space; can increase maintenance requirements through frequent repainting or cleaning to combat mould growth; and can make affected areas uninhabitable or even unusable due to poor air quality. In selective problem areas, the usual approach to the treatment of water intrusion problems is to 'trench and drain', in other words, to excavate and expose the wall area and the base of the foundation, to replace waterproofing on the wall surface, and to install a drain tile system around the building or affected area. Other areas, such as floors, are untreatable using conventional methods. Electro-osmotic pulse (EOP) technology offers an alternative solution that can mitigate some water-related problems from the interior of affected areas without the cost of excavation. Further, by lessening water seepage through concrete walls and floors, indoor humidity is reduced, thereby alleviating corrosion damage to mechanical equipment, lessening mould problems, and enhancing indoor air quality. 1.2 Electro-Osmotic Flow If ions of one sign are preferentially adsorbed at a solid solution interface, a net charge or electric potential difference develops across the interface. This phenomenon is referred to as electro osmosis. It was found that when a potential difference is applied to electrodes immersed into an electrolyte solution on opposite sides of a porous plug or fine capillary tube, a flow of the solution results. Similarly when a solution is forced through such a barrier by hydrostatic pressure, a potential difference develops between the solution on one side of the barrier and that on the other. This is called the streaming potential. Descriptions of this phenomena are based on the concept of the electric double layer. A layer of ions of one sign is firmly adsorbed on the solid surface or particle, the sign of the charge depending on the nature of the surface and other conditions. The region as a whole is electrically neutral, and an equal number of opposite electric charges are present in an adjacent ionic atmosphere. This is called the diffuse layer. When the solid surface and fluid are in relative motion, there exists a velocity gradient, and a thin film of solution together with the ions it contains, is immobilised near the wall. Part of the ion atmosphere moves with the solution, and part effectively belongs to the surface. As a result the liquid phase and the wall have diferent net electric charge, and the application of an external electric field produces relative motion. Electro-osmosis was originally described in 1809 by F.F. Reuss in the Proceedings of the Imperial Society of Naturalists of Moscow based on an experiment that showed that water could be forced to flow through a clay-water system when an external electric field was applied to the soil. Further research has shown that flow is initiated by the movement of cations (positively charged ions) present in the pore fluid of clay, or similar porous medium such as concrete, away from the anode in the direction of the cathode. The water surrounding the cations moves with them. Electro-osmosis has been used in civil engineering to dewater dredging and other high water content waste solids, consolidate clays, strengthen soft sensitive clays, and increase the capacity of pile foundations. It has also received significant attention in the past as a method to remove hazardous contaminants from groundwater or to arrest water flow.

Chapter 2 THE TECHNOLOGY A system has been developed to apply electro-osmosis commercially to concrete structures by applying a pulsating electric field. It is called electro-osmotic pulse (EOP). The pulse sequence consists of a pulse of positive voltage (as seen from the dry side of the concrete), a pulse of negative voltage, and a period of rest when no voltage is applied. The positive voltage pulse has the longest interval and the negative pulse has the shortest interval. As a result of this, the pore fluid moves (on the average) in one direction. The amplitude of the signal is typically between 20 and 40 Volts DC (VDC). The positive electrical pulse causes cations (e.g., Ca++) and associated water molecules to move from the dry side towards the wet side, against the direction of flow induced by the hydraulic gradient, thus preventing water penetration through the below-grade concrete structure. One of the most critical aspects of this technology is the negative voltage pulse. This allows control of the amount of moisture within the concrete which prevents over drying of the concrete matrix and subsequent degradation. Figure 2.1 shows an example waveform for the pulsating electro osmotic pulse or EOP system. Figure 2.1: Generic EOP Voltage Waveform An EOP system is realized by inserting anodes (positive electrodes) into the concrete wall or floor on the inside of the structure and by placing cathodes (negative electrodes ) in the soil directly outside the structure. The density of the anode and cathode placement is determined from an initial resistivity test of the concrete and soil. The objective is to achieve a certain current density and thus create an electric field strength in the concrete sufficient to overcome the force exerted on the water molecules by the hydraulic gradient. Figure 2.2 illustrates the EOP process. Figure 2.2: Cross section showing the EOP process Currently, the reasons for the increased performance of the EOP system over standard DC electro osmosis for drying concrete are not well understood. However, it is speculated that the change in polarity results in the reversal of some of the chemical reactions occurring during electrolysis. It is also believed that the rest phase (no applied voltage) allows the system to equilibrate. As a result of these effects, undesirable side effects such as acid production and increased corrosion are avoided. Also, use of a pulse sequence might prevent the concrete from becoming too dry. Since EOP technology relies on the pore structure to move water, it will not stop water that enters through cracks, joints and penetrations. Standard water stopping techniques must be used in these locations. However, these crack repair techniques rely on the bond between the repair material and the concrete. Moisture in the concrete deteriorates that bond requiring periodic removal and replacement of the repair material. EOP technology keeps moisture away from the bond and maintains the effectiveness of the repair materials. In order for EOP to be effective in preventing water intrusion into a structure, there are certain conditions that must be met; (1) Capillary pores must be present in the medium to be dewatered (2) The medium must have a fixed surface charge (3) A double layer of ions must exist along the pore walls (4) The medium must be wet with dilute electrolyte (5) The current must be applied to minimize alteration of the pore solution Concrete, masonry and most stone used in construction as well as clay soils have the necessary fixed surface charge which, in turn creates the ionic double layer along the pore walls. Chapter 3 EOP SYSTEM INSTALLATION 3.1 Typical Floor Installation Below is a generic procedure for a typical floor installation of the EOP installation: 1. Repair any cracks or voids where obvious water penetration is occurring with mortar, grout, foams or epoxies. These materials must be compatible with the EOP system. 2. A resistivity test of the concrete and the soil is done to determine both the pattern of the anode cable and the number and locations of the cathode. One anode and cathode are temporarily installed in the concrete floor and soil, respectively, and are connected to an EOP Control Unit. The voltage and current in the circuit are measured and used to compute the concrete/soil resistivity. A lower resistance requires a more dense anode cable pattern and/or a higher number of cathodes. 3. Grooves are cut into the floor in the pattern that was determined from the resistivity testing. The anode cable is placed in these floor grooves. 4. Cathodes are installed below the floor, and if necessary, outside the structure. Floor installation is done by drilling holes through the floor at the locations determined by resistivity testing. The cathodes can then be installed into the soil through the floor. Cathodes can be installed outside the structure by driving them into the ground like an electrical ground rod or by installing through the wall in a manner similar to the floor installation. 5. The EOP Control Unit is mounted in a location suitable to both the user and the installer. 6. Wiring is run from the EOP Control Unit to both the wire anodes and the cathodes. By using properly insulated wires, these wires can be embedded in the grooves that are in the floor. 7. After all wiring is placed in the grooves, mortar is used to fill the grooves to within ¼ to ½ inch of the surface. Then a levelling agent is used to completely fill the groove and level the surface. 8. The EOP control unit is turned on, adjusted and calibrated. The system is now operational. Wall installation of the EOP system is similar to the floor installation. Chapter 4 TECHNOLOGY DEMONSTRATION 4.1 General During fiscal years 1994 and 1996, EOP technology was demonstrated at two Army sites; the mechanical room of a guest barracks at Fort Jackson, South Carolina and an office and storage area in the basement of the Health Clinic at McAlester AAP, Oklahoma. In both cases, the location of the groundwater intrusion was through the floor and walls of poured concrete basements. These demonstrations were performed under a technology demonstration program, and therefore a large research and development effort was not possible. Monitoring of system performance was performed in the field, as best as possible. Supporting laboratory work was not available nor was it possible. These demonstrations, and the EOP technology, are described in detail in Hock et al. (1998). This paper discusses the experimental measure- ments taken at McAlester AAP - The EOP system was installed in the basement of the Health Clinic at McAlester AAP during July 1996. At that time the basement had standing water in several areas; water seepage from cracking in the wall; efflorescence and high indoor relative humidity. Analysis of water infiltration revealed that only about half the basement was leaking, therefore the EOP system was installed only in the areas of infiltration. Rubber-graphite anodes were installed 13 cm above the floor and 28 cm on centre. The total number of anodes used was 95. Four copper-clad steel ground rods (cathodes), 2.44 m long, were driven into the soil in the crawl spaces adjacent to the concrete wall in selected areas. Large cracks were repaired by filling with epoxy or nonshrink grout. To assess the effectiveness and evaluate the limitations of EOP technology several system and environmental parameters were monitored. The corrosion potential of rebar was measured using a 33-cm long piece of 1.27-cm steel rebar which was grouted into the wall along with a Ag/ AgCI reference half cell. The half cell was installed so as to be behind the rebar, and separated from it by about 5 cm of concrete. (Three additional 15-cm segments of 1.27-cm diameter rebar were placed in other basement walls to provide different EOP conditions from which to measure the corrosion potential of the rebar.) The humidity inside the concrete wall was sampled using a dual humidity/temperature probe which was sealed in a small cavity in the wall. Since the cavity is sealed, the temperature and humidity of the cavity should be proportional to the temperature and moisture content of the concrete. Ambient room humidity and temperature sensors monitored the Environmental Health Office. The level of the water table directly outside the basement was also monitored. In addition to these sensors and probes, the electrical power consumption of the EOP Control Unit and power supply was tracked. All these monitoring devices, except the rebar corrosion potential were fed into a data logger that was installed on site and was remotely accessible via modem. The data was collected and stored in the data logger until uploaded to a computer .The rebar to ha1f-cell potential measurement could not be properly interfaced to the data logger because of ground reference problems. The daily rainfall, average outdoor temperature, and average outdoor relative humidity at nearby McAlester airport were obtained from the Oklahoma Climatological Survey. Data was downloaded monthly from their INTERNET site. 4.2 Data Presentation and Discussion The most significant data from the McAlester field test is presented in Figures 4.1 and 4.2. These figures show the output power of the EOP system and the daily rainfall for a one year period. In addition to calculating energy costs, output power can be used to qualitatively evaluate the moisture content of the concrete. Because the system driving voltage is constant, the power output is directly proportional to the moisture content of the concrete. (Power is directly proportion al to current; current is inversely proportional to resistance; and resistance is inversely proportional to moisture content.) A drop in power therefore indicates that the concrete is drying out, i.e. the resistance is increasing. Conversely, a rise in power indicates moisture absorption by the concrete. This effect can be seen in the data for May through August 1997, where the power increases following large rainfalls, and then decreases as the system drives the water out. The most likely explanation for the few inconsistencies in power versus rainfall can be explained by the location of the rain gauge, which is located about 8 km from the base at McAlester airport. Because thunderstorms in the plains are localized events, the rainfall at McAlester AAP can differ from that at the airport. Water table data indicated that intrusion was not caused by a high water table. (At the Fort Jackson demonstration site, basement flooding occurred yearly because of the very high water table, often rising 1.5 m above the level of the mechanical room floor.) The water table never rose nearer than 0.65 meters below the basement floor, confirming that the water intrusion problem at McAlester was due to the saturation of the surrounding soil following rainstorms, as reported by the building's occupants. Occupants also reported that the heavy rainfall at the end of May 1997 was a rainfall that normally would have "flooded" the basement, however the water was held back by the EOP system. Results of the other experiments were inconclusive: l. Indoor absolute humidity was found to correspond directly with outdoor absolute humidity, as is shown in Figure 4.3. (Relative humidity was converted to absolute humidity ill order to eliminate temperature dependence.) 2. Cavity humidity did not vary directly with power as was expected. Figures 4.4 and 4.5 show the absolute humidity (i.e., temperature dependence removed) of the wall cavity. Cavity temperature data indicates a strong correlation with room temperature and the sudden drop in absolute humidity in March corresponds to the end of the heating season. 3. Results of the rebar corrosion potential experiments were inconclusive. There is evidence that the Ag/ AgCl half cell is not compatible with the concrete and might be drifting from its reference potential. Measurements were also taken using a Cu/CUSO 4 reference half cell, not only at the long rebar segment but also at the other three shorter segments, two of which were placed in non-EOP system walls. Measurement results were inconsistent, due possibly to the noise of the measurement technique, +1- 200 m V.

Figure 4.1: EOP Control Unit output power and local rainfall for November 1996 through April 1997

Figure 4.2: EOP Control Unit output power and local rainfall for May through October 1997

Figure 4.3: EOP Control Unit output power and indoor and outdoor absolute humidity for November 1996 through April 1997

Figure 4.4: EOP Control Unit output power and indoor and absolute humidity of the wall cavity for November 1996 through April 1997

Figure 4.5: EOP Control Unit output power and indoor and absolute humidity of the wall cavity for May through October 1997

4.3 Other Success Stories EOP technology has been installed in numerous Department of Defense (DoD) facilities where this cost-effective, non-intrusive waterproofing technology prevents moisture intrusion in below-grade structures. In 2003, an EOP system was installed in 100 feet of a Washington, DC, Metropolitan Area Transit Authority (WMATA) tunnel. Because the tunnel was constructed in bedrock and the concrete walls were greater than 2 ft thick at that point, the cathodes were placed deep in the tunnel walls. Monitoring of the EOP system in a Washington Metropolitan Area Transit for a year showed the average relative moisture content decreasing with respect to the EOP system commissioning time, approaching the typical moisture content of 70% at 2-in depth in the wall. The EOP system forces the water toward the exterior so that the interior concrete surface remains dry while the exterior stays wet. EOP's ability to reduce interior surface moisture below 55% makes the technology ideal for mold and mildew remediation and prevention. The ability to control water flow in large, deeply buried underground concrete structures or submerged structures such as lock walls led to innovative designs being implemented in two lock and dam structures on the Mississippi River (with concrete walls about 8 ft and 17 ft thick) and in a buried military command/control bunker. CERL and OsmoTech are currently monitoring the performance of EOP technology in these applications, which resulted in some special, innovative probe electrode designs: special plate cathodes were designed for submersion applications and are being monitored for performance in the locks of the two structures. In 2003 and 2004, the Directorates of Public Works at Fort Sill, OK, Fort McPherson, GA, Fort Gillem, GA, and Bolling AFB implemented EOP technology in family housing to take advantage of its low cost (about 40% less to install than traditional exterior "trench and drain" waterproofing methods), and its ability to control water migration in below-grade structures, to reduce indoor humidity (thereby eliminating mold growth can occur and improving air quality in the family housing units). ERDC-CERL, in partnership with OsmoTech, successfully installed EOP systems in the basements of family housing units at these three bases: 276 at Fort Sill, 76 at Fort McPherson, 10 at Fort Gillem, and 20 at Bolling AFB.

Chapter 5 COST/BENEFIT ANALYSIS 5.1 Background EOP technology should be used selectively. A properly designed and constructed building foundation with appropriate damp-proofing will correct most water problems inherent in the traditional designs of many foundation systems. However, severe problems in existing basements may require a more serious approach to mitigate moisture danger. In these selective problem areas, the common approach to mitigation is to excavate to expose the wall area and the base of the foundation, and then to replace the damp-proofing on the wall surface and to install a drain tile system around the building or affected area. This is a costly endeavour. Furthermore, most contractors severely limit their warrantee against future seepage in areas with high water tables. In buildings with daily occupancies and mature landscaping, retrofitting (by trenching and draining) a foundation is not easy. Any interior applications that can mitigate water-related problems will save the cost of excavation. Further, if the alternative can mitigate corrosion damage to mechanical equipment along with humidity and mould problems, it will yield benefits beyond the initial cost savings. 5.2 Comparison of Standard Water-Proofing Technology to EOP Technology The comparison is based on field experience at Fort Jackson and at McAlester AAP. 5.2.1 Standard approach estimate The following is a breakdown of the cost for mitigation without using the EOP system: 1. Site Dewatering: Where there is a serious seepage, a dewatering system must be installed before excavation. This consists of well points, drain headers, and rented pump equipment. 2. Wood Shoring: Assuming the structure has an 8 feet foundation wall with wet soil, at least 25 percent will have to be wood shored (maybe more to provide access and protect workers). 3. Excavation and Backfill: Generally in a constructed facility with underground utilities and limited mechanical access, one will have to hand excavate adjacent to the walls and to the utility lines. Assuming the building will still be occupied during this process, some disruption of normal services will likely occur. This will come to an average estimated cost of $125/cu yd. 4. Drain Tile Installation: A plastic perforated drain tile in a gravel bed at the edge of the footing will cost from around $4.19 to $4.31/linear foot. Steel, clay and concrete pipe are reasonable but more expensive alternatives. 5. Damp-proofing: Common practice is to apply a coating to the exterior surface of the exposed foundation wall. Alternate approaches based on soil condition and water content might be a fluid elastomeric, a bituminous coating or in severe conditions an EDPM membrane applied to the wall. On an average $1.00/sq ft is used for the estimate. 6. Backfilling: Assume mechanical backfilling with some tamping of the soil.($1.10/linear foot) 7. Landscaping Restoration: Restoration consists of reseeding, fertilising and replanting shrubs for the building perimeter. Table 1 gives the breakdown of the costs for each facet listed above. Table 1: Standard Approach Cost Estimate

5.2.2 EOP Technology estimate The prices in Table 2 reflect the cost of the EOP system and labour only. Table 3 gives the price comprising of the EOP Control Unit, anodes, ground rods, and all the wiring and labour for installation. The life cycle of the equipment and the pulsing technology system is estimated to be greater than 10 years, which means it requires zero maintenance during that period. The system consumes energy equivalent to that of a 60W light bulb left on all the time. But this cost is minimal and hence has been disregarded in the estimate.

Table 2: Costs of EOP Technology Installation

Table 3: Calculation of EOP system based on Installed Costs and lf of Wall

Some intangible benefits of the EOP system that might also be considered are: 1. There is minimal disruption of the building activity during the drying out process, e.g.: no digging, minor noise and a small amount of waste. 2. Illness caused by allergies or other sensitivities will be reduced, thereby increasing health and productivity of the building occupants. In summary, both the economic benefits based on conservative estimates from field data, and the intangible benefits, point to a very positive return-on-investment for the EOP technology.

Chapter 6 DEHUMIDIFICATION FOR ENHANCEMENT OF EOP TECHNOLOGY IN UNDERGROUND STORAGE FACILITIES Dehumidification (DH) is a mature technology that has been demonstrated to prevent corrosion of critical assets using a simple approach. Moisture levels in the air are maintained at a level that disables the corrosion chemical reaction by eliminating the electrolyte needed to enable corrosion. The technology has been commercialized in the private business sector and is available in a number of configurations and sizes. The simplicity of the process is shown below in Figure 6.1. Desiccant materials, such as silica gel, have a high affinity for water vapour. Desiccant materials, such as silica gel, have a high affinity for water vapour. The desiccant material dries the high relative humidity air stream by attracting and retaining the water vapour in the air as the air passes through it. The same desiccant materials are then exposed to a lower relative humidity air stream (or the “reactivation” air stream), which has the effect of drawing the retained moisture from the desiccant and drying it for the next batch of high humidity air. In the approach shown above a desiccant wheel is employed to continuously rotate and refresh the desiccant media for continuous operation. The configuration shown can apply to either a “closed system” where the same air is circulated over and over again so that the reactivation inlet air has already been dried by the system, delivered to the storage space, and returned to the system to dry the desiccant, and then reprocessed (dried) before it is circulated back into the storage space. This is the most efficient approach for most applications, but was considered undesirable for the ammunition storage facilities because of safety concerns associated with the potential accumulation of toxic or otherwise dangerous gases coming from the items stored. Therefore, an “open system” has been utilized whereby fresh air is used for the process inlet air source, and fresh air is likewise used as the reactivation inlet air source.

Figure 6.1: Dehumidification Technology Using Desiccant Chapter 7 BENEFITS AND BARRIERS OF THE EOP SYSTEM The following benefits are expected from the EOP System: * The prevention of structural damage by reducing rebar corrosion and concrete cracking. * The prevention of corrosion damage to interior mechanical and electrical equipment by reducing relative humidity. * Prolong the life of standard concrete repair technologies. * The improvement of interior air quality for the safety for occupants and workers. * Ease of EOP installation which causes less disruption to operations. The following are the barriers in the use of the EOP technology: * EOP system is not available in the market. It is not commercialized yet. * Appropriate assessment should be preceded before the application of EOP system application was decided. For example, if the reason of water intrusion into the basement is due to certain degree of the damage of concrete structure, it could be recommended to repair the structure first.

CHAPTER 8 EOP PROCESS ILLUSTRATION

Figure 8.1: Water Entry into Basement

Figure 8.2: EOP Process

Figure 8.3: EOP Pore Action

Figure 8.4: Plot of Concrete Moisture vs. Time for 15 Ft. of Head Pressure

Figure 8.5: Plot of Concrete Moisture vs. Time for 30 Ft. of Head Pressure

Chapter 9 CONCLUSION EOP has been shown to prevent moisture seepage into below-grade structures. It is effective in drying concrete and maintaining its relative moisture at below 50 percent humidity content, meaning the treated space stays dry, indoor relative humidity stays low, and no mold or mildew can grow. Testing in an earth covered magazine was performed to evaluate the effects of EOP system operation. The test results indicate the following: * There is no danger of a spark being generated by the EOP system. * There is no significant interference between the EOP system and the lightning grounding system of the ECM. * The EOP system will dry the interior surface of the concrete in ECMs where it is installed and keep it dry. * Optimum cathode placement for the EOP system was demonstrated to be inside the ground ring. * Hydrogen gas generation by the EOP system is unlikely as the reinforcing steel potentials are always well above the generation potential. * The steel corrosion rate is not affected by the EOP system. * EOP does not produce any interfering radio frequencies. The cost of installation has been determined to be 40 percent lower than the cost of the conventional trench and drain approach. The operating or energy cost of the EOP system is negligible- equivalent to the expenditure of burning a 60W light bulb. Thus the application of the EOP technology for control of water seepage in concrete basement structures is an acceptable alternative to the conventional trenching and tiling approach.