Page 375 - Construction Waterproofing Handbook
P. 375

REMEDIAL WATERPROOFING  8.35
                            Gunite or shotcrete mixtures used with this equipment vary from field ratio mixes to
                         premixed manufactured dry materials requiring only the addition of water. Materials are
                         applied as a dry mix for vertical applications. After initial application, materials are trow-
                         eled or finished in place as necessary.
                            Surface preparation requires chipping and removal of all unsound substrate areas and
                         repairing of existing reinforcing steel as necessary. Additional reinforcing steel may also
                         be installed if necessary before gunite operations.

                         Overlays
                         Cementitious overlays are used for restoring deteriorated horizontal concrete substrates.
                         Overlays are available in a wide range of mixtures containing various admixtures that add
                         strength and shorten curing time. They are used in a variety of applications including
                         bridge repairs and parking deck restorations.
                            Often they are sufficiently watertight to eliminate a need for waterproofing coatings.
                         Others are designed specifically for use as an underlay for deck coating applications. If
                         additional structural strength is necessary, qualified engineers should be consulted for
                         selection and use of such products.
                            These materials are usually self-leveling, conforming to existing deck contours to
                         which they are applied. They are used also to fill ponding or low areas of existing decks
                         before deck-coating application, Fig. 8.38. Stiffer mixes are available for ramp areas and
                         inclined areas. (See Table 8.10.)


             ELECTRO-OSMOSIS

                         Electro-osmosis is a process that introduces electric current into a substrate to control the
                         flow of water and humidity, a process originally identified in the early 1800s. The electro-
                         osmosis process is now available commercially and used for a variety of construction tech-
                         niques including removal of hazardous contamination from groundwater and facilitating
                         dewatering of soils.
                            Electro-osmosis is also used today as an effective remedial waterproofing and humidity
                         control method, but only for concrete structures at or below-grade. The process creates a
                         pulsating direct current (DC) electrical current that causes cations within the concrete to
                         move from the dry or interior side of a structure to the wet or exterior side. The movement
                         of cations attracts the available water and moisture to follow, against the flow induced by
                         the hydrostatic pressure, eliminating water infiltration into the structure.
                            A commercial electro-osmotic pulse system (EOP) consists of a control unit that plugs
                         directly into a common 110-volt outlet that delivers electric pulses to an anode (positive

                                   TABLE 8.10  Cementitious Systems Properties
                                         Advantages                  Disadvantages
                                   Variety of systems available  No movement capability
                                   Negative or positive systems  Only masonry and concrete substrates
                                   Large or small repair areas  Mixing controlled at site
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