Steel fiber reinforced concrete : properties, application, advantages and disadvantages

Concrete is the most widely used material in the world. The concrete has a very low tensile strength which tends to sudden failure without warning. thus, we require to add material that can resist the tensile forces for the concrete.

Steel is mostly used with concrete due to its high tensile strength. Depending upon the purpose of the use of concrete we can modify the properties of steel.

There are so many techniques are available to achieve the desired strength and durability. fiber reinforced concrete is one of them.

Fiber-reinforced concrete is used in various applications. Depending upon the purpose, Different types of fibers are used such as steel, glass, polypropylene, nylon, asbestos, coir or carbon, etc.


Steel fiber reinforced concrete 


SFRC contains concrete mortar and discontinuous and discrete steel fibers. it is not the substitution for the reinforcement. we can use fibers with and without the reinforcement depending upon the nature of use.
  
The use of fibers in the concrete mortar is not for the purpose of gaining tensile strength only. the major use of fibers in concrete is to reduce crack development and to make the concrete a lightweight.

SFRC is composite concrete, which contains disperse fibers. These fibers transfer the stresses, which is very useful to reduce the crack development.

SFRC Image credit - https://www.indiamart.com/proddetail/fiber-reinforced-concrete-frc-8892556088.html
Steel fiber reinforced concrete ImageCredit- Indiamart

The mixing of fibers with concrete is a very essential part to avoid the unnecessary loss of strength. For example, if the fibers are not mixed properly then the area, where these steel fibers are not available, can reduce strength in that particular area. and also workability of the concrete can be reduced.

The modulus of elasticity or young's modulus of the steel fiber reinforced concrete is higher than that of traditional concrete.

Affecting factors such as aspect ratio, the volume of fibers, mixing, the orientation of fibers should be considered before the mix. with SFRC, the admixture also can be used to achieve the desired quality of the concrete.

Steel fibers properties


Steel fibers are discrete, short in length, round in shape, aspect ratio from 20 to 100, diameter from 0.25 to 0.75mm which are dispersed in the concrete during the mixing process.
 
Steel fibers are bundled together with the help of water-soluble glue which further separated during the mixing process of the concrete.

The typical properties of the steel fibers are, tensile strength of 280 to 420 Mpa, poisson's ratio is 0.30, young's modulus of 200 Gpa, ultimate elongation of 3.6 %, specific gravity of 7.86.

The fibers will transfer the stress as shown in the figure below.

Steel fiber reinforced concrete- stress distribution
Steel fibers behavior


The manufacturing technique for the steel fibers is cut wire/ cold drawn. the product should be purchased as per the application. steel fibers are available in the shape of round, rectangular (0.3 to 0.5 mm thick), also available in deformed bundled form.

The shorter length fibers are used to control the cracking while longer length fibers are used to gain high anchorage between fibers and concrete. The mix design can be done according to the purpose of use.

Types of steel fibers


ASTM A820 classified five different types of steel fibers,
  • Cold drawn wire
  • Cut sheet steel
  • Mill cut
  • Melt extract
  • Modified cold drawn wire
Due to the shape and composition, the cold drawn wire has the highest tensile strength. hooked steel fiber can make better anchorage between fibers and concrete and also available at low cost. thus, this type of fiber is mostly used. 

Depending upon the use, steel fiber has a different shape and size as shown in the figure below. Hooked, non-straight or crimped, button end, indented, straight, puddled, twisted polygonal, etc.

Steel fiber shapes
Shapes of steel fibers

Mechanical properties of SFRC


By adding fibers in concrete, the mechanical properties of SFRC can be enhanced depending upon the previously discussed factors.

According to research, the compressive strength, and shear strength can be increased up to a certain limit.

Arranged fibers in the concrete results in higher tensile strength as compare to randomly mixed fibers.

Impact loading resistance and increased fatigue strength were observed from the research. also, a reduction in permeability was observed.

According to the study, flexural strength was increased higher as compare to the direct tensile strength of the concrete. also, enhancement was found in toughness and the durability of the SFRC with a certain amount and arrangement of the fibers.

Advantages


The following are the advantages of using steel fibers in concrete.
  • Reduction in cost and timing of the project.
  • Reduce the absorption of water and the other harmful chemical.
  • Reduce the surface permeability and increase the durability of the concrete.
  • Reduce curling and eliminates shrinkage stress.
  • Increase in fatigue strength, flexural strength, toughness, load-bearing capacity, etc.
  • Prevent the development of cracks in concrete.
  • fibers are a distributor of localized stress.

Disadvantages


The following are the disadvantages of steel fiber reinforced concrete.
  • The corrosion at the surface of the concrete.
  • Proper inspection while mixing is needed.
  • Requires precise composition.
  • An increase in the number of fibers can reduce the workability and can cause the finishing problem. 

Application


Steel fiber reinforced concrete is used widely nowadays. some of the common application of the SFRC are as follow.

  • Pavement
  • Airfields
  • Overlays or roads
  • Bridge deck
  • Flooring
  • roads
  • Pipes
  • Sleepers
  • Septic tanks


SFRC is widely used in the construction or repair of roads or highways pavement. 

This material has high flexural strength, resistance toward impact, which makes this material more useful to roads and highways pavement. 

Also, the thickness of the pavement can be reduced using this material.

Due to its corrosion resisting capacity, this material can be useful where water and corrosion are major concerns like hydraulic structures.

SFRC also used in the making of precast concrete products.

Steel fibers are also used to make fiber shotcrete, which used in tunnel lining, bridge, pipes, stabilization of rocks, dams, steel structure protection, etc.

Steel fibers are also used in the rebar reinforced concrete to improve the mechanical properties and use them in the structural application.


Conclusion


From the above article, 

The steel fiber reinforced concrete is a very popular material to be used in the concrete due to its satisfactory and acceptable mechanical properties. This material is efficient to improve the mechanical properties of the concrete. 

It is also useful to make strong, thin, and lightweight concrete. SFRC has a broad application, as we discussed above.

Other types of fiber-reinforced concrete such as Glass fiber reinforced concrete and Polypropylene fiber reinforced concrete have been discussed previously.

Further discussion could be done in the comment section.





 

 


 

   





 






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