Globally, fibers have been used in construction materials for a long time, especially as reinforcement to improve the properties of these materials. Since the Egyptian period, natural fibers, such as straw and horsehair, were already incorporated into the formation of clay bricks, for example. Straw was also a material used in early Japanese and Chinese buildings, for the purpose of reinforcing structural components of houses. Since then, we have also started to apply to fiber for concrete.
This is because each construction material has properties in which it is deficient and others in which it stands out. For example, a key property by which the concrete is recognized for its high compressive strength. On the other hand, it has low tensile and flexural strength. It is to help improve these properties that various types of materials are used to compose fiber for concrete.
For this reason, these fibers are standing out as a component material. As it happened with the additives liquids, fiber for concrete should become an increasingly applied input.
Continue reading the article and learn more about fiber for concrete and how it can improve specific properties of this material. Follow up.
Why use fiber for concrete?
When comparing the properties of simple or common materials with other fiber-reinforced materials, there are a wide range of benefits. The delay and control of tensile cracking in composite material are among the most significant results of the fiber associated with concrete.
Other potential gains include:
- Improved characteristics and properties: such as resistance (to traction, compression, bending), toughness, durability, stiffness, and ductility;
- Control and resistance to cracks and shrinkage, fragmentation, and swelling;
- Thermal characteristics and fire resistance;
- Better performance in different environments;
- Improved stability;
- More protection against physical and chemical corrosion and other attacks;
- Decrease in specific weight and density, resulting in a lightweight product that is energy and cost efficient;
- Reduction and lower design and installation costs, as fibers can replace traditional reinforcement methods.
As for these potential outcomes, a few issues need to be kept in mind. Firstly, when fibers are added to the concrete mix, their content must be decided with caution, since the content influences workability of the mixture - and to improve it, additives may be required.
It is also important to remember that, as much as concrete fiber can improve its properties, there is no miracle: using poor quality concrete and applying fibers will not solve the problem. The fibers will reinforce or enhance properties, but the basis for this must be of quality.
Main materials used in the composition of fiber for concrete
Concrete fiber is available in different materials, diameters and lengths. It can also be applied simultaneously, combining its properties according to the needs of the project.
Steel fibers and polypropylene fibers, as well as structural synthetics, are some types most commonly used in structural elements. But in addition to these, there is a wide variety of materials, which include glass, nylon, sisal, polyester, and others.
Next, discover more about some of the main types of materials that can make up fiber for concrete:
Natural fibers
Natural fibers are found in the environment and are normally extracted from the outside of plants, trees, and straw. They include coconut, sisal, palm, jute, flax, straw, bamboo, cane, and more.
Natural fibers are more readily available and abundant, require little or no energy to produce, can be extracted from waste, are economical and low-cost, and help reduce environmental impact and are a sustainable option.
However, it should be noted that the main disadvantage of these fibers is that they normally have little durability and, because they are natural, they can degrade with the action of time. Another disadvantage found in plant fibers is that they are hydrophilic.
Synthetic fibers
Synthetic fibers are manufactured and produced for a purpose. These include, for example, steel fibers, glass fibers, plastics, both plastic macrofibers and plastic microfibers, and carbon fibers.
In general, they have low elastic modulus and high elongation properties. Therefore, they have the potential to provide concrete with significant ductility. As a result, when added to concrete, these fibers are able to control the fissures caused by long-term thermal movements and drying shrinkage, improving concrete performance.
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It is commonly used to improve the mechanical properties of concrete. Properties, such as tensile strength, compression, impact, flexion and final load capacity can be improved with this fiber for concrete, as steel absorbs energy well and helps control cracking.
Toughness, abrasion, and impact resistance can also be improved, as can resistance to shear and puncture, in addition to the energy dissipation capacity and durability of concrete structures.
Steel fibers are also quite unique, and can be used for specific applications, as they have magnetic, thermal and electrical properties. Furthermore, the expansion of the size of slab it is also possible with the addition of steel fibers.
As a disadvantage, which is similar to that found in traditional reinforcement, is the corrosive potential of steel fiber.
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Glass fibers have good mechanical properties and stand out in terms of strength, thermal properties and durability.
They are generally used to reinforce polypropylene systems. A composite is formed between the elements to result in a material with differentiated properties.
The resulting composite is economical, easy to produce, and has the strength and toughness characteristics of fiberglass. As a disadvantage, there is the potential for degradation and low resistance in alkaline environments.
Polypropylene
Polypropylene fibers are widely used in civil construction, especially in concrete applications and mortar to manage and reduce the formation of retrenchment and plastic cracks.
Concrete reinforced with polypropylene fibers tends to show significant improvement in certain properties, including increased strength, toughness, impact resistance, and watertightness. They are also recognized for their more affordable cost.
Polypropylene concrete fiber is also alkali resistant, cost-effective, improves abrasion resistance, and reduces fragmentation.
Another important point to highlight is that fire situations are still among the most serious risks for tunnels, buildings, and other concrete structures. Thus, risks related to increased temperature must be considered when designing concrete structures, including explosive chipping due to adverse concrete deterioration.
For this demand, polypropylene fibers can be useful, since they are very effective in mitigating fragmentation in concrete exposed to high temperatures, helping to avoid displacement.
However, some drawbacks of using polypropylene fibers in concrete may arise due to their low density, including fluctuation problems within the composite matrix that may reduce the workability and adhesion of concrete due to its low hydrophilic characteristics.
Difference between microfiber and macrofiber in concrete
When we evaluate the materials that can make up fiber for concrete, it is also important to understand the difference between these fibers.
Synthetic fibers can be categorized into two types based on their geometry, which are microfiber and macrofiber.
Microfibers are commonly less than 0.3 mm in diameter. They are used especially to minimize early cracks, to control plastic shrinkage (cracks that may occur within the first 24 hours of Concrete curing), protection against impact and fire, due to its anti-fragmentation potential and to improve the homogeneity of the concrete during application. However, they should not be used to replace any structural steel elements.
In turn, macrofibers, also called structural fibers, have a diameter greater than 0.3 mm and can be used to replace traditional reinforcement in certain non-structural applications.
Therefore, when fibers are used instead of wire mesh and/or steel rebar, for example, macrofibers are the recommended option.
In addition, they also help to minimize or eliminate early and late cracks and to improve durability and toughness and are resistant to oxidation.
Among the disadvantages of macrofibers, it tends to be more laborious to dose concrete, due to the influence of the fiber on the rheology of the material in the plastic state, and it may present difficulties in homogenization. Still, there is a limitation on the size of the plates, generally between 8 and 10 meters.
And then, did it become clearer to you what are the materials that can make up fiber for concrete? To learn more about this topic, continue to follow our blog.
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