Steel fiber reinforcements enhance the impact capacity and toughness of concrete
Steel fiber reinforcement reinforced concrete is a castable or sprayable composite material consisting of hydraulic cement, fine aggregate or fine and coarse aggregate, with discrete steel fiber reinforcements of rectangular cross-section randomly distributed throughout the matrix. steel fiber reinforcements strengthen concrete by resisting tensile cracking. FRP concrete has a higher flexural strength than unreinforced concrete and concrete reinforced with welded wire fabric.
1. The effect of steel fiber reinforcements on concrete.
steel fiber reinforcements are commonly used in concrete to control cracking due to plastic shrinkage and drying shrinkage. They can also reduce the permeability of concrete, thereby reducing water seepage. Certain types of fibers produce greater impact resistance, abrasion resistance and crushing resistance in concrete. Typically, fibers do not increase the flexural strength of concrete and therefore cannot replace moment resistance or structural reinforcement. In fact, some fibers can actually reduce the strength of concrete. The amount of fiber added to the concrete mixture is expressed as a percentage of the total volume of the composite (concrete and fiber) and is called the volume fraction (Vf). It can range from 0.1% to 3%. The length-to-diameter ratio (l/d) is calculated by dividing the fiber length (l) by its diameter (d). steel fiber reinforcements with a non-circular cross section use the equivalent diameter to calculate the L/D ratio. If the modulus of elasticity of the steel fiber reinforcements is higher than that of the matrix (concrete or mortar binder), they help to carry the load by increasing the tensile strength of the material. An increase in the length-to-diameter ratio of steel fiber reinforcements usually increases the flexural strength and toughness of the matrix. However, excessively long steel fiber reinforcements tend to agglomerate in the mixture and create workability problems.
2. Reinforcement mechanism in steel fiber reinforcement reinforced concrete.
In the hardened state, when steel fiber reinforcements are properly bonded, they interact with the matrix at the microcrack level and effectively bridge these cracks, thus providing a stress transfer medium that delays their agglomeration and unstable growth. If the steel fiber reinforcement volume fraction is sufficiently high, this may result in an increase in the tensile strength of the matrix. In fact, for some high volume fraction fiber composites, a significant increase in tensile/bending strength has been reported over a normal matrix. Once the tensile capacity of the composite is reached and agglomeration and conversion of microcracks to macrocracks has occurred, the steel fiber reinforcements continue to inhibit crack opening and crack extension by effectively bridging the macrocracks, depending on their length and bonding properties. This post-peak macro-crack bridging is the primary reinforcement mechanism for most steel fiber reinforcement reinforced concrete composites.
3. Effect on steel fiber reinforcement processability.
Slump tests were performed to determine the workability and consistency of the fresh concrete. The efficiency of all steel fiber reinforcement reinforcement materials depends on the uniform distribution of fibers in the concrete, their interaction with the cement matrix, and the ability of the concrete to be successfully placed or sprayed. Essentially, each steel fiber reinforcement needs to be coated with a cement paste to provide any benefit in the concrete. Regular users of steel fiber reinforcement reinforced concrete will be fully aware that adding more fibers to concrete, especially very small diameter fibers, will have a greater negative impact on workability and the need for mix design changes. Slump changes due to differences in fiber content and form. The reason for the lower slump is that the addition of steel fiber reinforcements creates a network structure in the concrete, which inhibits segregation and flow of the mixture. Due to the high fiber content and large surface area, the steel fiber reinforcements will definitely absorb more cement paste package and the increase in viscosity of the mixture will cause a loss of slump.
4. The effect of steel fiber reinforcements on the impact capacity and toughness of concrete.
Toughness is a measure of the ability of a material to absorb energy during deformation estimated using the area under the stress-strain curve. Based on tests conducted on the mechanical properties and impact resistance of steel fiber reinforcement reinforced high performance concrete. Five different geometries of fibers including steel plate cut fibers and ingot milled fibers and four fiber volume fractions (4%, 6%, 8% and 10%) were applied to the mixture. When the fibers were used in the blended form, the increase in the above studied parameters was about 31.42% compared to normal concrete.
5. Advantages of steel fiber reinforcement reinforced concrete.
(1) Fast and perfect mixable fibers and high performance and crack resistance.
(2) Optimized cost with lower amount of steel fiber reinforcements.
(3) steel fiber reinforcement enhances concrete from impact, thus improving the toughness properties of hardened concrete.
(4) steel fiber reinforcements reduce permeability and water migration in concrete, thus ensuring protection of concrete due to the adverse effects of moisture.
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