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| Fiber Reinforced Concrete |
Fiber Reinforced Concrete
Introduction
Fibre Reinforced concrete are the mixture of cement concrete with the mix of Fibrous materials distributed uniformly for nearly 0.1- 0.5% of the total volume of the concrete. The main aim to use FRC is that, we know when we place a normal concrete or a normal mix or cement mortar, All of them are brittle in nature tending to show high compressive strength but are weak with Tensile Stresses.
The Increased tensile stresses leads to crack later on resulting in failure of the concrete.
I give you a simple example - When we apply cement mortar for brickwork, we will see few cracks started to show on the surface, that use to be for two majorly reasons of lack or curing and uneven disruption of tensile load. Even there we use the fibrous materials in the mix and chicken mesh in joint surface to overcome the cracks.
The fibrous material behaves as a bridge between the cracks generated in concrete which increase the flexural toughness of concrete.
If you are thinking about what is flexural toughness than it is the ability to absorb the stresses coming to the concrete which results in plastic deformation of the fiberous materials resulting in decreasing the cracks.
What is fibre reinforcement
Fibre Reinforcements are flat or circular in shape made of different materials such as steel, glass, asbestos, carbon, polypropylene etc which are determined on there aspect ratio’s of length to breadth . The fibrous materials improves the fire resistance of concrete, It Resists in preventing the increase of crack widths, Reduces the shrinkage cracks.
Factors which control the parameter of Fiber Reinforced Concrete.
1) Type Of Fibre
The type of fiber which we are using for fiber reinforced concrete plays a major role. These fibrous materials are used based on the characteristics they posses and the requirement for the work.
The short, thin fibers which shows low modulus of elasticity are highly preferred when there is only the requirement of resistance from fire or crack resistance whereas the Long synthetics fibers having high modulus of elasticity such as glass, steel widely plays a key major role absorption of the stress coming to the surface as they are uniformly distributed in concrete.
2) Volume Of Concentration Of Usage of Fibre reinforcement
The volume or the quantity of fiber reinforcements we use in the concrete is directly proportional to the flexural toughness of the concrete member and the gain in tensile strength.
The more quantity we use in the mix, the better toughness we increase for the concrete but the disadvantage of this is that the high quantity of fibers reduce the concrete workability and later leads to segregation of concrete.
Volume of Fibers | Area of Usage |
>1 % | l Chances of having shrinkage cracks l Used in slabs etc |
1% - 2% | l Used in Shortcrete Technique l To overcome deterioration of concrete in layers. |
<2% | l Used in high performance FRC. |
3) Aspect Ratio
Aspect ratio of these Fibrous materials are the ratio of the length to the width of the fibers. It has been observed that the more the aspect ratio the better strength and flexural toughness we get. But they have a limitation that the increase is only till 75 range of aspect ratio. After 75 it starts decreasing.
You can get nice idea by seeing the table.
Type of Concrete | Aspect ratio Length/breadth | Relative Strength | Relative Toughness |
Concrete with uniform distributed Fiber reinforcements | 0 | 1 | 1 |
25 | 1.5 | 2 | |
50 | 1.6 | 8 | |
75 | 1.7 | 10.5 | |
100 | 1.5 | 8.5 |
4) Orientation of fibers
The orientation of fibers is the way in which the fibers are aligned in the concrete mix. This orientation of the fiber reinforcements can be of different types such as
l Fiber reinforcements aligned to the direction of the load acting to the concrete
l Fiber reinforcements aligned to the perpendicular direction of the load acting to concrete.
l Fiber reinforcements randomly mixed in concrete
As the orientation of fibers also govern the Fiber reinforcement Concrete, therefore it is observed that when the orientation of these fibers are parallel to the load acting on the concrete, they posses the high tensile strength and the toughness to the concrete as compared to the different orientations such as randomly or perpendicular to the concrete.
Note - To achieve maximum optimization of Fibre Reinforcement concrete, The fiber should be at 90 degree angle to the cracks.
Fiber Reinforced Concrete- Mechanical Properties
1) Compressive Strength
It has been observed that the compressive strength of the concrete increases with the increased of fibers in the concrete from 1% - 32% . This increase is achieved when the fibers are used from the range of 0.5% to 1.5% of the concrete volume. Study shows the short size fiber reinforcements posses more compressive strength compared to long size.
2) Other Mechanical Strength
Mechanical Property | Increase in Fibers | Increase of Property in % |
1)Compressive Strength | 0.5% - 1.5% | 1% - 32% |
2) Modulus Of Elasticity | 1% | 3% |
3) Flexural Strength | 4% | 2.5 times Volume |
4) Splitting Tensile Strength | 3% | 2.5 times Of un-reinforced concrete |
5) Toughness | 0.5% - 1.5% | 10 to 40 times of normal concrete |
6) Fatigue Strength | 0.5% - 1.5% | About 90% of concrete |
7) Impact Strength | 0.5% - 1.5% | 5-10 times of Normal concrete |
Applications of Fiber Reinforced Concrete
l Used in spray Concrete as it improves ductility.
l Used inside traffic tunnels since they are fire resistant.
l Used in roads, slabs, pavements as it sows resistance to cracks.
l Decrease the quantity of reinforcement used.
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