1. The function of PP fiber concrete
Concrete is one of the main raw materials in modern architecture. Modern building construction get bigger, higher and more complex. PP fiber concrete can apply to modern buildings and improve concrete durability.
After adding short, thin PP fibers into the concrete, its performance will get better. Adding fiber to cement-based materials is to overcome concrete weakness. As a result, prolong its service life and expand its application field. Polypropylene fiber concrete has stronger crack resistance, reinforcement, and toughening effects than ordinary.
1.1 Crack resistance
Polypropylene fibers hinder the generation and propagation of micro-cracks in concrete. And this crack resistance occurs throughout the hardening stage of concrete.
1.1.1 Crack Resistance of Polypropylene Fiber in Plastic Concrete
(1) Among the polypropylene fibers, there are polypropylene fibers distributed. These fibers present a three-dimensional network structure in the concrete structure. It plays the role of supporting aggregate. And its effect is to prevent the settlement of the coarse and fine aggregate. That is the coarse aggregate sinks first, and then the fine bone material. Meanwhile, polypropylene fibers can also reduce water precipitation on the concrete surface.
This phenomenon of separation of water and materials is called segregation. Segregation affects the homogeneity of the concrete. There is more cement paste or finer aggregates on the surface of the concrete. The surface loses water rapidly. Thus occurs larger shrinkage, resulting in more cracks on the concrete surface. Such cracks are usually called settlement cracks. The addition of polypropylene fibers can prevent and inhibit concrete segregation. So it reduces or even completely prevents the generation of cracks on the concrete surface.
(2) PP fiber bears the tensile stress caused by shrinkage in the plastic state of concrete. Thus reducing the number of cracks.
The tensile strength of the cement matrix is low within 24 hours after pouring. And when its moisture evaporates rapidly, it is easy to produce a large number of cracks. The fibers can withstand the tensile stress caused by plastic shrinkage. And the shrinkage energy is dispersed to the PP fiber monofilament. They have high tensile strength and low elastic modulus per square meter. Thereby preventing or reducing the generation of cracks.
1.1.2 Crack Resistance of Polypropylene Fiber in Hardened Concrete
After the concrete has hardened, temperature and humidity changes can cause drying shrinkage. Drying shrinkage will cause tensile stress. When this stress exceeds the tensile strength of the fiber, a large number of cracks will occur. In this case, pp fibers can still prevent cracks from forming.
Hardened Concrete will experience drying shrinkage, temperature shrinkage, and carbonation shrinkage.
1. Drying shrinkage
Evaporation of water inside the concrete will cause the cement matrix to dry out and shrink. If the internal tensile stress exceeds the tensile strength, concrete will produce cracks.
2. Temperature shrinkage
A sudden drop or rise in temperature during use will affect concrete structure. When the outside temperature drops, it will cause the concrete to shrink. This environmental change will cause temperature stress in the concrete. It results in many cracks in the concrete. The temperature shrinkage cracks are usually small at the beginning of formation. And the width does not exceed 0.5mm. But after repeated drying and cold shrinkage, the cracks will expand and wide.
3. Carbonation shrinkage
PP fiber concrete can prevent carbonation and shrinkage of concrete. Hydration of cement in concrete produces calcium hydroxide. Carbon dioxide in the air reacts with calcium hydroxide to form calcium carbonate. Calcium carbonate has twelve percent less volume than calcium hydroxide. The reduction in volume causes the concrete to shrink. And, under constraints, can also lead to cracks in the concrete.
Note; the premise of shrinkage is that there is a certain amount of moisture in the concrete.
PP fiber concrete can reduce the stress concentration at the tip of micro-cracks. It prevents the expansion of micro-cracks and the occurrence of connected cracks. Once concrete has cracks, the front end of the cracks intersects with the fibers. The tensile stress that causes the cracks can be weakened or eliminated. PP fiber also control the development of cracks. The cracks
larger than 0.05mm are greatly reduced. Achieving the purpose of anti-crack and anti-seepage.
The distribution of PP fiber is uniform and thorough. There are nearly 20 fiber filaments in each cubic centimeter of cement slurry. So a uniform chaotic support structure can be formed inside the concrete mortar. Thus forms an effective secondary reinforcement effect. This structure can prevent the segregation of aggregates. It ensures the early and uniform bleeding of concrete. Thereby hindering the formation of settlement cracks. The crack resistance of PP fiber concrete is 70% higher than that of ordinary concrete.
Ordinary concrete has low tensile strength and internal voids. PP fiber concrete can improve the tensile, flexural, and fatigue strength of concrete.
Under load, even if the concrete cracks, PP fibers can still span the cracks and bear the tensile stress. To make concrete has good toughness. Toughness is an important index to characterize the deformation resistance of materials. Polypropylene fiber concrete can improve the toughness of concrete. It improves the ability to resist cracking and deformation. Especially for improving the brittleness of high-strength concrete.
1.4 Freeze resistance
Polypropylene fiber concrete alleviates the impact of temperature changes. It prevents the expansion of micro-cracks. The improvement of the impermeability of PP fibers also improves frost resistance. In cold regions such as the northern US, the use of PP fiber concrete can reduce frost cracking.
1.5 Waterproof and Anti-seepage capabilities
PP fiber concrete can enhance the waterproof and anti-seepage capabilities of concrete. Polypropylene fiber concrete can enhance water and seepage resistance. Construction workers generally incorporate large amounts of polypropylene fibers into concrete. This fiber can inhibit the drying shrinkage and segregation cracking of concrete. It can reduce shrinkage cracks, especially the appearance of continuous cracks.
The polypropylene fibers are evenly distributed in the concrete and connected. PP fiber reduces the water separation and segregation on the concrete surface. As a result, the voids with a diameter of about 100 nanometers in the concrete are greatly reduced. And the impermeability is improved. Our customers found that adding 0.05 percent polypropylene monofilament fibers to concrete. The impermeability of the concrete is increased by 60% to 70%. This anti-seepage ability is especially prominent in basement projects and water storage tanks
1.6 Shock and earthquake resistance
The polypropylene fiber concrete is hard. The high-strength PP fibers wrapped in the cement will stick to each other. They form a dense random network structure. This structure can prevent the generation and development of microcracks. and enhance the toughness of concrete. The surface strength of polypropylene fiber concrete is stronger than ordinary concrete.
It can keep more water and reduce the occurrence of aggregate segregation. Polypropylene fibers can make fibers and cement bonded together. The strength of polypropylene fiber concrete become better. When shocking polypropylene fiber concrete, the fibers absorb a large amount of energy. So it reduces the effect of concentrated stress and prevents the rapid expansion of cracks. Enhanced the seismic and impact resistance of concrete. This property is especially important for some concrete structures (such as sidewalks, parking lots, etc.) that are subject to impact fatigue.
1.7 Wear resistance
PP fiber concrete improves the wear resistance of concrete and mortar surfaces. It reduces dust, scales, flakes, and other damaged images.
1.8 Good correction
Polypropylene monofilament fiber is a kind of polypropylene fiber. Other rigid additive materials will expose the surface of concrete components. But, PP fiber does not affect concrete appearance. The fine structure of PP fiber combined with proper rest. This can make the visual effect of concrete surfaces softer and more pleasing to the eye.
PP fiber for plaster has a simple construction operation. It can provide high plastering efficiency, less mortar drop, and strong crack resistance. It can replace steel wire mesh. It is important for improving staff efficiency, ensuring project quality, and reducing costs. Based on very important meaning.
Polypropylene monofilament fiber is a kind of high-strength polypropylene fiber. The raw material is 100% polypropylene. It has strong resistance to acid and alkali. The product has been tested by acid and alkali for 120 days without any damage or aging. The chemical properties are very stable. It only depends on changing the physical structure of concrete to improve the performance. and it will not absorb other substances. It will not conflict with concrete aggregates, admixtures, admixtures, and cement. So it has good properties with concrete. affinity.
2 Modified PP fiber concrete
2.1 What is Modified PP fiber concrete
Polypropylene fibers are usually surface treated with silicone materials. First, select a specific solvent for dissolution. Then soak the fiber or spray on the surface of the fiber. Take out and set aside. Don't place the treated fibers in a humid environment. Humid conditions disrupt the hydrolysis of silicone materials.
After modification, the polypropylene fiber is in a semi-suspended state in water. And the color becomes darker rapidly. At this time, it is easy to distribute evenly in the cement, and the degree of bonding with the cement is also good. The fiber dissolves faster in water added with surfactants such as water reducers. And it is easier to stir.
2.2 Advantage of Modified PP fiber concrete
The chemical properties of modified PP fiber concrete are better than those without modification. It has high impact strength and good loosening resistance. The tensile strength, chemical corrosion resistance, and freeze-thaw resistance have also been improved. The modified polypropylene fibers can increase the strength of concrete by 10% to 20%.
3. Properties of PP fiber concrete
- Reduce early shrinkage cracks, temperature cracks and long-term shrinkage cracks;
- Improve crack resistance performance and ultimate strain. The bending toughness is increased several times to dozens of times. When damaged, the matrix cracks but does not shatter;
- Improve bending fatigue and compression fatigue performance;
- It has excellent impact resistance, explosion resistance and penetration resistance;
- Improve wear resistance, cavitation resistance, erosion resistance, freeze-thaw resistance and impermeability of concrete;
- Improve the durability of concrete.
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