ABSTRACT This paper summarizes 1995 through 1998 laboratory, outdoor exposure facility, and field data on the subject concrete rehab system. The system shows promise as a means of providing cathodic protection to the reinforcing, as a chloride removal process, as a re-alkalization process, and/or as a lithium injection procedure to minimize alkali-aggregate reactions in the concrete. Unique characteristics of the system include:
1. Surrounding each galvanic anode with a highly corrosive liquid which maintains it (the anode) at peak output voltage throughout its life; and
2. Placing an ionic transfer layer between the anode and the concrete surface that is high volume, low resistivity and deliquescent (i.e. pulls water vapor out of the air at relative humidities of 35??ZOor higher). The ionic transfer layer typically consists of sponge, felt or sand loaded with calcium chloride (and/or other chemicals such as sodium hydroxide, potassium acetate, and lithium-salts). In some cases it also contains a wetting agent and is encapsulated (fully or partially) in vapor permeable, but water impermeable materials. The ionic transfer layer will not freeze at temperatures as low as -20 C (?5 ?F), and provides sufficient space for all anode corrosion products, thus preventing undesirable stresses on the concrete, the anode assembly and any cosmetic covering.
INTRODUCTION Cathodic protection is technically proven means of mitigating the corrosion of steel in waters, soils and moist, chloride contaminated, reinforced and prestressed concrete structures both above and below water and soil.l?2
Work on adapting galvanic (sacrificial) anodes to reinforced and prestressed concrete structures began in the mid- 1970s.3 Although such anodes could be made to work, problems with low current ~~put and accommodation of the anode corrosion products prevented widespread use of the technology .
The alternative to a galvanic anode system is an impressed current cathodic protection system in
which power from an outside source is used in concert with low corrosion rate anodes. 1-8 This
alternative overcomes the difficulties of low power output and accommodation of anode corrosion
products. Many impressed current systems have been installed. However, they are somewhat
complicated and generally require continuing monitoring.7?8
Present galvanic anode systems for atmospherically exposed concrete, such ass rayed zinc, will work in hot, moist environments, such as the Florida Keys and similar coastal areas.9 -* However, many are too low power for complete corrosion control on high corrosion rate, above-water and soil concrete structures in the central and northern portions of the United States, and on structures with multiple mats of reinforcing steel.
The causes of low power output area low voltage or potential difference between the sacrificial anode and the corroding steel in salty concrete, oftentimes only 0.5 volts or less. In addition, concrete, even when wet, has a higher resistivity (resistance per unit area) than most wet soils and natural waters, up to 100,000 ohm-cm or more; and significant contact resistance exists between many sacrificial anode systems and concrete. These factors create a large circuit (anode to cathode) resistance that results in low current output.
Temperature greatly affects concrete resistivity. The lower the temperature, the higher the resistivity and thus the lower the current output. The resistance is increased if the concrete layer immediately beneath the sacrificial anode dries out. Additionally, some sacrificial systems have the shortcoming of a finite life that often is less than the life of the structure involved. If the sa