A composite material containing mixtures of cement, mortar or concrete and discontinuous, discrete, uniformly dispersed good fibers is called Fiber Reinforced Concrete. Fiber-reinforced concrete is of various types and properties with huge advantages. Continuous meshes, woven fabrics and long wires or rods are not taken to be discrete fibers.
Some of the substances made by chemical synthesis fibers are utilized in concrete are carbon, nylon, polyester, polypropylene, and polyethylene.
i) Huge fiber volume micro-fiber system.
ii) It can remove asbestos fiber.
iii)It improves toughness and impact strength.
The necessity of Fiber Reinforced Concrete
- It arises the tensile strength of the concrete.
- It decreases the air voids and water voids.
- It arises the durability of the concrete.
- Fibers such as graphite and glass can withstand to creep, while the same is not good for most resins. Therefore, the inclination and volume of fibers have a notable impact on the creep performance of rebars.
- Reinforced concrete is a composite material, where the reinforcement work as the strengthening fiber and the concrete as the matrix, therefore this imperative that the behavior under thermal stresses for the two materials be the same so that the differential buckling of concrete and the reinforcement are smaller.
- It has been acknowledging that the sum of small, closely spaced and uniformly dispersed fibers to concrete would work as a crack catcher and would substantially revamp its static and dynamic properties.
Factors Affecting Properties of Fiber Reinforced Concrete
Fiber-reinforced concrete is the compound material containing fibers in the cement matrix in a proper manner or randomly distributed manner. Its properties would depend upon the efficient transfer of stress between the matrix and the fibers. The factors are briefly discussed below:
1. Relative Fiber Matrix Stiffness:
The modulus of elasticity of the matrix must be much lower than that of fiber for efficient stress transfer. Less modulus fiber such as nylons and polypropylene are, therefore, dissimilar to provide the strength improvement, but they help in the soaking up of huge energy and therefore, impart a more degree of toughness and withstand to impart. Huge modulus fibers such as steel, glass, and carbon impart strength and stiffness to the composite.
The associate bond between the matrix and the fiber also calculates the effectiveness of stress transfer, from the matrix to the fiber. A better bond is important for improving the tensile strength of the composite.
2. The volume of Fibers:
The strength of the composite largely depends on the number of fibers used in it. Show the result of volume on the toughness and strength. It can arise in the volume of fibers, arise approximately linearly, the tensile strength and toughness of the composite. The use of a more percentage of fiber is similar to cause segregation and harshness of concrete and mortar.
3. Aspect Ratio of the Fiber:
Another essential factor that impacts the properties and behavior of the composite is the aspect ratio of the fiber. It has been noted that up to an aspect ratio of 75, an arise in the aspect ratio arise the ultimate concrete linearly. Beyond 75, relative strength and toughness are decreased.
4. The orientation of Fibers:
The differences between conventional reinforcement and fiber reinforcement are that in conventional reinforcement, bars are positioned in the direction desired while fibers are properly oriented. To look at the effect of randomness, mortar specimens reinforced with a 0.5% volume of fibers were tested.
5. Workability and Compaction of Concrete:
The incorporation of steel fiber decreases the workability considerably. This situation adversely affects the consolidation of a fresh mix. Even prolonged external vibration is unsuccessful to compact the concrete. The fiber volume at which this problem is reached is conditional on the length and diameter of the fiber.
6. Size of Coarse Aggregate:
The maximum size of the coarse aggregate should be restricted to 10mm, to remove an appreciable reduction in strength of the composite. Fibers also in effect, act as aggregate. Although they have a normal geometry, their impact on the properties of fresh concrete is difficult. The inter-particle friction between fibers and between fibers and aggregates controls the orientation and distribution of the fibers and consequently the properties of the composite.
Mixing of fiber reinforced concrete requires careful conditions to remove balling of fibers, segregation and in general the difficulty of mixing the materials uniformly.