Traditionally concrete has been successfully reinforced with steel bars and/or welded wire fabric set into the concrete where analysis indicates high tensile stress or high impact loads. However even well designed bar-reinforced concrete systems will manifest cracking over time.
For many applications, it is becoming increasingly popular to reinforce the concrete with small, randomly distributed fibers. Their main purpose is to increase the energy absorption capacity and toughness of the material along with superior crack resistance.
The concept of Fiber-Reinforced concrete is not new, rather from a historical perspective it appears much like a contemporary version of an old theme. Historical records dating back to biblical times clearly attest to the practice of using “straw” in building blocks. Even Roman building practice incorporated a type of “fiber” – horsehair, which was widely used in the construction of many imposing structures notably the Colloseum. Through the ages therefore, the use of fibers has been a recurring theme from straw in adobe, hair of wild animals to the host of modern synthetic fibers.
Steel-fiber-reinforced concrete is a state-of-the-art composite material made of hydraulic cements, fine or coarse aggregate, and a dispersion of discontinuous steel fibers. It may contain pozzolans and additives commonly used with conventional concrete. The amount of fiber in concrete mixes typically ranges from 0.5% to 2% by volume, although smaller amounts have been used successfully in reduction of plastic- and drying-shrinkage cracking. According to the Portland Cement Association, steel fiber contents greater than 2% result in poor workability and fiber dispersion within the concrete mix.
However, the main effect of adding steel fibers in concrete, that is also the main advantage of SFRC and the most useful regarding design of hyperstatic construction (like slab on ground), is its post-crack behavior or toughness of SFRC. Steel fibers in concrete start acting when the first crack appears and have the ability to absorb and redistribute the loads (or energy), so that the SFRC will still be able to bear loads even after the formation of cracks. In fact, SFRC has a ductile behavior or toughness and therefore, that surplus of flexural capacity from the plastic phase (post-crack ductility) can be used for design of structure when deformation must be controlled like slabs or for structures where deformations controlled the design like underground linings. It is the reason why, for the same thickness, a SFRC slab on ground can support higher loads than a conventional concrete slab.
The addition of these fibers provides improvements of the engineering properties of the concrete such as impact strength, toughness (post-crack ductility), ability to resist cracking and material disintegration, as well as fatigue resistance. The exact amount of increased strength depends on many variables, especially fiber content. With fiber contents of 1.5% to 2% by volume, direct tensile strength will increase 30 to 40%, and flexural strength (first crack) will increase 50 to 150%.
Benefits of SFRC Floors
To the Owner
- Less Cost , High Quality, Longer Life of Floors
- Resistance to micro cracks propogating into macro cracks
- Provides high impact resistance
- Excellent surface finish can be achieved
- Eliminates spalling due to corroding reinforcement
- Reinforces the edge helping to prevent joint failure
To the consultant
- Cusomized Design Support
- Suitable for wide range of applications
- Ease in designing for complete life span of Concrete Floors
- Ensures Optimum use of material and Technology.
- Reduce steel reinforcement requirements
To the contractor
- Faster construction
- Reduced labor cost
- Easy to handle, mix, place and finish variety of Floors surfaces.
- Environmentally friendly
- Compatible with all surface finish and coating techniques.
The most significant factor affecting resistance to crack propagation and strength of the fibrous concrete and mortar are
- Shape and bond at fiber matrix interface
- Volume fraction of fibers
- Fiber aspect ratio and Orientation of fibers
- workability and Compaction of Concrete
- Size of Coarse Aggregate