NEFMAC

NEFMAC, or New Fiber Composite Material for Reinforcing Concrete, is made from glass, aramid, or carbon fibers (or combinations of each) impregnated with an appropriate resin system, such as polyester, vinylester or epoxy to form a grid (Fig. 3.61). The method of production, shown in the schematic in Fig. 3.62, is a batch process. A series of continuous fibers are dispensed from individual creels by a mechanical system through a wet-bath to be deposited by two orthogonal traveling (winding) heads in a grid pattern. The heads move at synchronized speeds that define the size of the grid. Successive movement of the heads results in fiber cross-over and the placement of interlocking layers until the desired content/cross-sectional area is achieved. The process is capable of line speeds in excess of 2 m/min. with about 200 m² of grid being produced per hour. Cure is achieved through the use of UV or radiant heat.

Fig. 3.61. Examples of NEFMAC grids.

Fig. 3.62. Schematic of the "Pin-Winding" process used in the production of NEFMAC.

Characteristics and Material Properties

Since NEFMAC is available in the form of a grid, it shows very good anchorage and mechanical interlock in concrete. Furthermore, due to its resistance to corrosion and excellent resistance to alkalis, acids and chemicals, it does not require substantial cover. Its light weight (specific gravity < 2) facilitates ease and speed in construction, without loss in performance. Although the most common form of NEFMAC is a grid, it is also available in a variety of shapes and forms (including a 3D reinforcement cage). Since it is fabricated using continuous non-metallic fibers, it is non-magnetic and can be used in areas where the use of conventional steel reinforcement would pose a problem. A variety of fibers (listed in Table 3.21) can be used as reinforcements in NEFMAC.

The glass fiber types are predominant for use in non-structural or secondary structure applications. Carbon reinforcements are preferred for primary structure. This is due to aspects related to mechanical performance and long-term aging, such as creep and environmental durability.

Although polyesters, vinylesters and epoxies are all used, vinylesters are the preferred resin system due to their cost structure, processing ease and general performance characteristics. In grid form, the glass fiber reinforced NEFMAC has a specific gravity of 1.7. The carbon fiber variety has a specific gravity of 1.4. The nominal fiber volume fraction in all grids is about 40%. NEFMAC grid panels are available with grid spacings of 50, 100 and 150 mm, reinforced with glass [G], carbon [C], aramid [A], or hybrid glass-carbon [H] reinforcement fibers in a variety of configurations, as listed in Table 3.22.

Fig. 3.63. Representative stress-strain response.

Applications

NEFMAC grids have been used in tunnels, runways and aprons for airstrips/tarmacs, roads, buildings, channels, rehabilitation, and for general architectural elements. They are often used as lightweight reinforcement in building fascia and curtain walls, where the lower requirements for cover applications result in thinner and lighter panels. The use of NEFMAC grids in the fabrication of such panels is shown in Fig. 3.64; the lightweight concrete building panels are shown being placed on a steel framed building in Fig. 3.65. Due to their non-magnetic properties, NEFMAC grids have been used as reinforcement in hospitals and in free-access floors, as well as in sensitive structures such as scientific laboratories and observatories (Fig. 3.66). In coastal areas and regions where rapid corrosion of steel reinforcement is a concern, NEFMAC elements can be used by themselves or in combination with heavier steel bars. For example, in the coal silo of the Daio-Paper Mill on Shikoku Island NEFMAC elements were used for the outermost reinforcing layer, which also served as a barrier for crack propagation (Fig. 3.67).

Fig. 3.64. Use of NEFMAC in the fabrication of a lightweight concrete curtain wall panel.

Fig. 3.65. Placement of NEFMAC reinforced curtain wall panels in a building frame.

Fig. 3.66. Use of NEFMAC as a reinforcement in the foundation of the Earth Magnetism Observatory.

Fig. 3.67. Use of NEFMAC as secondary reinforcement in a concrete silo structure in a coastal region.
The light weight, environmental resistance and ease of fabrication facilitated through the use of NEFMAC elements makes it an attractive reinforcing element for adverse conditions which could otherwise hamper construction. For example, at the South Pole the climate itself causes embrittlement of steel rods and makes rapid construction (including welding) difficult. NEFMAC panels were used extensively in the construction of the Showa Antarctic Base in 1991 as seen in Figs. 3.68-72. Not only was fabrication of foundations and walls easier because of the light weight and ease of placement, but there was also a greater assurance of quality and future performance without the severe degradation seen in conventional reinforcement. C10 and C16 varieties of NEFMAC (see Table 3.22) were used in the construction of floating foundation slabs, columns and column bases, walls and floors.

Fig. 3.68 . Schematic of the Administration Block Building for the Polar Base Facility.

Fig. 3.69. Use of NEFMAC in the foundation base.

Fig. 3.70. Use of NEFMAC 3D forms in the column.

Fig. 3.71. Use of NEFMAC grid as wall reinforcement.

Fig. 3.72. Use of NEFMAC as reinforcement in the floor.

Due to their excellent corrosion resistance, these grids, especially carbon fiber reinforced NEFMAC, have been used extensively in marine structures. Applications range from their use as reinforcement for fender plates and pier panels to their use as the primary reinforcement for concrete in a floating pier structure in Tokyo. In this latter example, 2,100 m² of G2-50P NEFMAC grids were used as reinforcement in pontoons (built in 1989) as shown in Figs. 3.73-75.

Fig. 3.73. Schematic showing geometry of the pontoon.

Fig. 3.74. View of a single pontoon fabricated using NEFMAC grids as reinforcement.

Fig. 3.75. Overall view of the floating jetty.

Due to its non-corrosive nature, light weight, resistance to alkalis, water, oil, and sludge, and the capability of manufacturing grids to conform to a variety of shapes and contours, NEFMAC is often used as the reinforcement for shotcrete, both in repair and retrofit and for new linings and coverings. For this application, after the application of an appropriate but undisclosed safety factor, the G3 and G4 grades of NEFMAC with performance levels of 4,000 kg/m and 6,000 kg/m strength per width are more than equivalent to the strength levels shown by conventional welded wire fabric (2,513 to 5,890 kg/m). In this form of construction, a layer of shotcrete is first sprayed onto the surface to be covered. Then NEFMAC grids/elements are stapled to the shotcrete substrate using an air gun with compressed air loaded with staples 19 mm to 38 mm long and 16 mm wide between heads having a cross-section of 2.1 mm by 1.8 mm. Due to the light weight and ease of conformance, relatively few staples are needed. Then a thin covering coat of shotcrete is sprayed on. The use of thin layers of shotcrete, coupled with the ease in placement of the NEFMAC, dramatically increases worker productivity. Figure 3.76 shows the grid structure used for tunnel linings fabricated with this technique.

Fig. 3.76. NEFMAC grid for tunnel lining reinforcement.

Figures 3.77-78 show NEFMAC used as reinforcement for a shotcrete lining in an underground oil storage facility and the pilot tunnel leading to the facility. This facility is owned by Dengen Kaihatsu in Kagoshima Prefecture and uses G3 and G4 grades of NEFMAC. The overall cross-section is shown schematically in Fig. 3.79, which also indicates the use of rock bolts through the walls.

Fig. 3.77. Use of NEFMAC as lining reinforcement in an underground storage facility.

Fig. 3.78. Use of NEFMAC as lining reinforcement in the pilot tunnel (note the irregular face of rock).

Fig. 3.79. Schematic of cross-sectional configuration.

The shotcrete method also can be used for the rehabilitation and repair of tunnels using pre-stapled NEFMAC grids to form linings/walls (Fig. 3.80). The method also has been used for the fabrication of new tunnel linings for penstocks and tunnels for water supply in hydroelectric power plants (Figs. 3.81-82). Examples of the early use of this method (known as NATM) are given in Table 3.23.

Fig. 3.80. Use of NEFMAC in the repair/retrofit of a railway tunnel.

Fig. 3.81. Use of NEFMAC as reinforcement for the lining of tunnel walls in a hydroelectric plant.

Fig. 3.82. Use of NEFMAC as reinforcement in the floor of a tunnel used for transport of water.

The light weight of NEFMAC has also been used advantageously to prefabricate tunnel lining segments and provide reinforcement between segments during the repair of a tunnel on the Japan Railway Sobu Line (Figs. 3.83-85).

Fig. 3.83. Placement of a prefabricated tunnel liner panel.

Fig. 3.84. Use of NEFMAC at joints between panels.

Fig. 3.85. Completed lining.

Besides its use in tunnels as part of a shotcrete or precast system, the grids have been applied to shotcrete for reinforcing dam slopes and embankments (Figs. 3.86-88), and walls of in-ground excavated storage tanks (Fig. 3.89).

Fig. 3.86. Application of NEFMAC for reinforcing the downstream slope of a dam.

Fig. 3.87. Application on a slope.

Fig. 3.88. Placement of shotcrete covering on NEFMAC used for slope reinforcement.

Fig. 3.89. Use of grid as reinforcement for the wall of an excavated storage tank.

2D and 3D grid elements also have been used as reinforcements in systems for slope protections and stability (Fig. 3.90-92).

Fig. 3.90. Placement of 3D grid reinforcement cages on a slope.

Fig. 3.91. Partially completed slope protection system using NEFMAC reinforced concrete.

Fig. 3.92. Completed slope protection system.

NEFMAC grids have recently been used in the repair and rehabilitation of concrete decks. In the case of the Tedorigawa Bridge (initially constructed as part of the expressway system in 1972), corrosion due to salt had severely degraded the concrete deck soffit. About 20,000 m² of C3-50P (carbon fiber reinforcement with 50 mm grid spacing) grids were used in a polymer mortar for the rehabilitation. The grids were anchored to the original concrete using dowels with 60 mm heads, and were covered with a mortar for which they served as a base and reinforcement. In the case of the Niiborigawa bridge, the girders themselves were deteriorating. The lower 5 cm of each girder was chipped away and the reinforcement was exposed. NEFMAC grids (C3, C6 and C10) were placed on the exposed surfaces using dowels (Fig. 3.93-94) and precast concrete forms were placed on top. The area in between the NEFMAC grid and the concrete surface was then filled with polymer mortar through injection.

Fig. 3.93. NEFMAC grid attached to the bottom of the exposed beam.

Fig. 3.94. Rehabilitation of the Niiborigawa Bridge.

In another application, specially shaped NEFMAC elements were used as the reinforcement for the guideway on a prototype linear motor rail line on which speeds are expected to reach 500 km/hr. NEFMAC reinforcements were chosen because of their non-magnetic characteristics and ability to be molded for complex shapes. About 100,000 carbon fiber reinforced units consisting of grids and hoop reinforcement were used over a distance of 18 kilometers.

Similar to the NOMST (Novel Material Shield-Cuttable Tunnel Wall System) technology developed by Nippon Steel, NEFMAC can also be used to reinforce shaft walls, facilitating easier access through a shaft wall using a shield/bore, which can cut through the composite reinforcement without deterioration of bits in the rotary cutter. Not only does this application conserve resources, it also increases safety (previously a chip and brace method was used for the entrance) and speeds up the entire process without resorting to chemical grouting. A schematic of the process is shown in Fig. 3.95.

Fig. 3.95. Schematic of the reinforcing scheme for shaft walls.

In this kind of application, NEFMAC is generally in the form of a flat grid with spacing at 50, 100 and 150 mm. But a variety of curved panels are also available for specific geometries. Panels are primarily reinforced with carbon fiber using grades C10, C16, C22, C25, C29 (see Table 3.22) used in conventional applications of NEFMAC and special grades C32 and C35 (having sectional areas of 395 and 480 mm², maximum load capacities of 47.4 and 57.6 tons, and weights of 561 and 682 g/m, respectively). Glass fiber reinforced grids are rarely used. But when they are, G10, G16 and G19 grades are the common choices. Figure 3.96 shows a large wall section fabricated from multiple grids, and Fig. 3.97 shows the placement in a caisson wall.

Fig. 3.96. Lifting of a multi-element wall section.

Fig. 3.97. Placement of NEFMAC "wall."

Figures 3.98 and 3.99 show the placement of reinforcing elements for shaft walls and depict double layers and connection details.

Fig. 3.98. Placement of NEFMAC in shaft walls.

Fig. 3.99. Reinforcement detail near head of tunnel showing double layers.

Connections between two or more layers of reinforcement use specially shaped "stirrup" and "plinth" reinforcements (Fig. 3.100).

Fig. 3.100. "Stirrup" and "Plinth" connectors.

An extensive list of NEFMAC applications since 1986 is given in Table 3.24. Sizes and types of grids are also detailed. Some applications in Table 3.24 (marked "*") have been listed by various sources as having either glass or carbon fiber reinforced grids. Although it is clear that a large number of the projects listed in Table 3.24 are actual applications, rather than test sites, it is not clear which of the listed sites were limited demonstrations, validation tests, or even included test articles. No data was available on the economics of the technology itself. Although a preponderance of applications appear to have used glass fibers as reinforcement prior to 1994, applications since then appear to strongly favor the use of carbon fiber. It may be coincidental that this was about the time when Shimizu concluded an extensive study on aging and durability of NEFMAC material.