Types ,advantages and disadvantages of concrete fiber
Writer： admin Time：2025-01-27 10:05 Browse：
1. The technical feature of steel fiber reinforced concrete is that it can improve the toughness and tensile strength of concrete, but the steel fiber is easy to agglomerate when mixing, the workability of concrete is poor, pumping is difficult, difficult to construct and easy to rust, the self weight of steel fiber reinforced concrete and the use of a large amount of steel in manufacturing increase the consumption of steel and increase the cost. The failure mode of steel fiber in use is mainly pulled out rather than broken, which shows that the adhesion between steel fiber and concrete is insufficient, which will affect the effect of improving the tensile strength of concrete. The principle of toughening and strengthening is that when the crack occurs, the further development of the crack is prevented due to the high modulus of steel and the high tensile strength of a single root; However, due to the limited number, it has little effect on micro crack restraint, and the improvement of anti permeability, freeze-thaw and other properties is not obvious. In addition, the steel fiber density is too large in construction, and it often sinks in the lower part of the concrete during vibration and pouring, which is impossible to be evenly distributed. This is the main reason why the theoretical research conclusion is good and the practical application effect is very different.
2. Although glass fiber has been used to pave concrete pavement, glass fiber has exposed great disadvantages in use. For example, after glass fiber concrete is exposed to the atmosphere for a period of time, its strength and toughness will decrease significantly, that is, it will degrade from early high strength and high toughness to ordinary concrete. As we all know, ordinary glass fiber has another fatal weakness, that is, it is not alkali resistant. Alkali aggregate reaction is the "cancer" of cement concrete. Therefore, ordinary glass fiber can not be used as cement-based reinforcement. Even alkali resistant glass fiber (AR) is not suitable to be compounded with ordinary portland cement, and it is best to be compounded with low alkalinity cement. This is mainly to reduce the alkaline corrosion of cement substrate on the surface of glass fiber. China's "double insurance" technical route (i.e. alkali resistant glass fiber and low alkalinity cement composite) has been difficult to be popularized in a large area for decades because of the practice of "cutting feet to fit shoes". In addition, it is difficult to distinguish alkali resistant glass fiber from ordinary glass fiber in appearance.
3. Synthetic fiber includes polypropylene fiber, polyester fiber and polyacrylonitrile fiber. Its similarity with steel fiber is that it is not eroded by hydration products, has certain tensile strength, and can be distributed in the concrete matrix in three-dimensional random direction. Its crack prevention principle is to give full play to the advantages of the number of fibers (tens of millions per kilogram), has a large surface area and restricts micro cracks, Make it not connected, the effect is remarkable. However, the density of synthetic fibers is small, the diameter of monofilament is small, and thickening effect is not conducive to the vibration of concrete. Because of the low tensile strength of synthetic fibers, the main form of failure is fiber breaking, and it is also not good enough to resist aging and alkali resistance.
4. Carbon fiber is a high-performance fiber developed in the 1960s. It has the advantages of high tensile strength and elastic modulus, stable chemical properties and good bonding with concrete. However, due to the high price of carbon fiber, its engineering application is greatly limited.
From the performance of the above concrete fibers, it can be seen that these fiber concrete have some defects, which are not ideal in meeting the requirements of high-performance concrete, and can not well solve some existing problems. The development of fiber reinforced concrete for decades tells us that we must make a breakthrough in fiber in order to make fiber reinforced concrete, a high-performance concrete, widely used.
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