Fiber-Reinforced Concrete

Fiber-reinforced concrete (FRC) has a randomly oriented distribution of fine fibers in a concrete mix [5]. Fiber size varies with typical length less than 50 mm and diameter less than 1 mm. Many fibers have been used for concrete reinforcement (Table 1), with additions of 0.1-3% by volume of fibers, which improves the strength of the concrete by up to 25% and increasing the toughness by a factor of 4. This means that FRC is less susceptible to cracking than ordinary concrete showing longer service life.

Structural concrete is reinforced with steel to carry tensile forces that are internally generated when a structure undergoes elastic and inelastic deformations. Steel fiber-rein­forced concrete (SFRC) consists of cement containing aggregates and discontinuous steel fibers (low-carbon steels or stainless steel; ASTM A-820 [6] provides a classification for steel fibers). In tension, SFRC fails after the steel fiber breaks or is pulled out of the cement matrix. The strain and force interaction is complex and depends on factors such as chemi­cal and mechanical bond between concrete and reinforcement, time-dependent properties (creep, shrinkage), environmental aspects (freezing, chemicals), geometric configuration, location and distribution, and concrete/reinforcement volume ratio.

The applications of SFRC take advantage of the static and dynamic tensile strength, energy absorbing characteristics, toughness, and fatigue endurance of the composite [7]. Uniform fiber dispersion provides isotropic strength properties. The applications include

Fiber-Reinforced Concrete

Fig. 1 Flow diagram of main process

Table 1 Fibers for concrete reinforcement

Advantages

Disadvantages

Comparison of properties of selected materials [8]

Density Unidirectional tensile (g cm-3) strength (GPa)

Steel

Stainless

Steel

Provide very good, reasonably priced reinforcement Very good

reinforcement

Corrode over time, after 6-8 years provide little reinforcement Very expensive

8.0

207 (steel 4130)

Glass

fiber

Good

reinforcement

Alkaline nature of concrete causes the strength of silica-based fibers to degrade with time

1.99 (E – glass, S-glass)

52-59

Carbon and Kevlar

Excellent

reinforcement, high strength

Very expensive; brittle behavior (Fig. 2)

1.55-1.63

(Carbon)

145-207

Plastic fiber

Good

reinforcement

Low cost

1.38 (rein­forced epoxy aramid)

83

cast-in-place SFRC (slabs, pavements industrial floors), precast SFRC (vaults and safes for instance with fiber content from 1 to 3 vol%), shotcrete (a sprayed concrete developed for civil construction, for instance in slope stabilization and in repair and reinforcing of struc­tures), and slurry infiltrated fiber concrete (called SIFCON, where a formwork mold is ran­domly filled with steel fibers and then infiltrated with a cement slurry, containing a much larger fiber fraction between 8-12% by volume). Corrosion of steel reinforcement and the tendency of concrete to lose bond, and reducing structural performance over time, promote the development of economical, thermodynamically stable metallic and nonmetallic, corro­sion-resistant reinforcements. Therefore, other reinforcement has been developed such as polypropylene fibers (most common in the market), glass fibers, and carbon fibers.