Steel fiber is a new, high-performance steel fiber variety. The mixing ratio design method of steel fiber road is basically the same as that of ordinary concrete, but the differences are: double-controlled strength standards (compressive strength and flexural tensile strength); steel fiber content is determined according to the flexural and tensile strength required by the design; unit water consumption and sand The rate is related to the amount of fiber added. For every 0.5% (volume rate) steel fiber added, the unit water consumption increases by 6kg.
Steel fiber concrete has the same mixing, operation and construction performance as ordinary concrete. The fiber will not form balls in the concrete and is evenly distributed. It can be produced in commercial concrete mixing plants and can be used for pumping construction. The early slump loss of milled steel fiber reinforced concrete is larger, with a loss of 32% in 30 minutes and a loss of 42% in 2 hours. The actual workability of steel fiber reinforced concrete is better than that of ordinary concrete with the same slump. Compared with ordinary concrete, steel fiber reinforced concrete has good material properties. Compared with ordinary concrete, its compressive strength is increased by 2-20%; flexural tensile strength is increased by 20-50%; splitting tensile strength is increased by 20-40%; wear resistance is increased by 40% %, its physical and mechanical properties can fully meet the technical indicators of urban road engineering and inspection manhole covers and other supporting components. The rough and clean surface of steel fibers can be firmly combined with the cement paste in concrete, which is the fundamental reason for milling steel fibers to improve various properties of concrete.
In addition, high-strength steel brazing concrete has been widely used in railway sleeper prefabrication, highway expansion joints, cement concrete pavement and other prefabrication, cast-in-place, production and construction, etc. Its excellent performance can completely achieve good technical, economic and social environment. benefit.
A. Adhesion
Since the interface bond between the steel fiber and the concrete matrix is mainly physical, that is, the transmission of frictional shear force is the main factor, so for the steel fiber itself, the bonding performance should be improved from the two aspects of fiber surface and fiber shape. . There are the following four specific methods.
1. The surface of the steel fiber is roughened and the cross-section is irregular. This goal can be achieved by using the melting and extraction method. When the steel fiber is rapidly cooled in the air, the surface shrinks unevenly and becomes rough, and the cross-section also shrinks into a crescent shape, increasing the contact with the matrix.
Contact area.
⒉ The fibers are plastically processed at a certain distance along the axis of the steel fiber. For example, the "Xinke" steel fiber of Japan Kobe Steel Corporation's "XOREX" steel fiber of Leibang Corporation of the United States (Figure 2-1, c) and the "S-2" and "S--3" steel fibers of Qing'an Iron and Steel Plant steel fiber. Since the surface is pressed into a prismatic shape, or pressed into a wave shape, the mechanical bonding force is increased.
3. Shape the ends of the steel fiber. The "DRAM Ⅸ" steel fiber of Becker Gongdian in the United States (Fig. 2-1, e) and the "S-4" and as-so steel fibers of Qing'an Iron and Steel Plant are made of hooks at both ends. There are also The large-headed steel fiber extracted by the melting and pumping method improves the pull-out resistance due to the anchoring effect at both ends.
⒋ The surface of the steel fiber is coated with epoxy resin and the surface is micro-rusted. This method does not improve the interfacial bond strength as much as the previous methods, but it also has certain effects.
The tests of Ichifu Kobayashi, the University of Liege in Belgium, and Zhang Wengang have all proved that the effect of steel fibers with hooks is about twice as high as that of straight steel fibers. of steel fibers. These special-shaped steel fibers not only improve the strength of the steel fibers, but also improve the toughness. Although the corrugated steel fiber has little effect on improving the strength of steel fiber reinforced concrete, it can double the toughness.
B: Hardness
No matter which processing method is produced, the steel fiber will encounter high heat and rapid cooling during the processing, which is equivalent to the quenching state. Therefore, the surface hardness of steel fibers is higher. Bending rarely occurs during mixing for concrete reinforcement. If the steel fiber is too hard and brittle, it is easy to break when stirring. When the steel fiber is produced by the melting and pumping method, the steel fiber centrifugally ejected from the melting and pumping wheel is still in a high temperature state, and is dispersed and cooled by a roller or vibration conveying method. Otherwise, the steel fibers will gather, and the heat will be difficult to dissipate, which will instead play the role of annealing.
C: Corrosion resistance
The introduction of the corrosion resistance test of steel fiber reinforced concrete shows that the cracked steel fiber reinforced concrete components in a humid environment, the concrete at the crack is carbonized, the steel fiber in the carbonized area is corroded, and the carbonization depth and corrosion degree develop with time. For concrete, it mainly uses the post-crack radian and post-crack toughness. Although the crack width is smaller than that of reinforced concrete, there are cracks after all. Therefore, anti-corrosion measures should be taken for steel fiber reinforced concrete used in a humid environment, especially in the seaside. measure. The face test proves that, on the premise of ensuring that the steel fiber reinforced concrete members have the same bearing capacity, the use of steel fibers with larger diameters can improve corrosion resistance, and the use of epoxy resin-coated or galvanized steel fibers will improve corrosion resistance. If the construction technology permits, this steel fiber can be used only on the surface of the concrete 1-2cm, and if necessary, non-induced steel fiber can also be used.
