Main Properties of Steel Fibers

Ⅰ. Steel fiber is a new kind of steel fiber with high-performance

Steel fiber is a new kind of steel fiber with high-performance. The design method of the mix ratio of steel fiber roads is basically the same as that of ordinary concrete, but the differences are: double control standards of strength (compressive strength and flexural tensile strength); steel fiber content is determined according to the flexural tensile strength required by the design; unit water consumption and sand percentage are related to the fiber content. For every 0.5% (volume rate) steel fiber, the unit water consumption increases by 6kg and the sand percentage increases by 2%.

steel fiber reinforced concrete has the same mixing, operation and construction performance as ordinary concrete. The fiber will not be spheroidized in the concrete and is evenly distributed, which can be produced in a commercial concrete mixing station and can be used for pumping construction. The early slump loss of milled steel fiber reinforced concrete is relatively large, 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 ordinary concrete with the same slump. steel fiber reinforced concrete has good material properties. Compared with ordinary concrete, its compressive strength is increased by 2-20%; its flexural strength is increased by 20-50%; its splitting tensile strength is increased by 20-40%; and its wear resistance is increased by 40%, whose physical mechanical properties can meet the technical indicators of urban road engineering and inspection manhole covers and other supporting components. The rough and clean surface of the steel fiber can be firmly combined with the cement paste in the concrete, which is the fundamental reason why the milling of the steel fiber improves the various properties of the concrete.

In addition, high-strength steel fiber reinforced concrete has been widely used in the prefabrication, cast-in-place, production and construction of railway sleeper prefabrication, expressway expansion joints, cement concrete pavement. Good technical, economic and social environmental benefits can be achieved by its excellent performance

Ⅱ. Main performances of steel fiber

1. Adhesion

As the interface bonding between steel fiber of our steel fiber company and concrete matrix is mainly physical, that is, the transmission of frictional shear is the main factor. Therefore, for steel fiber itself, the bonding performance should be improved from such two aspects as fiber surface and fiber shape. There are four specific methods as follows.

(1) Make the surface of the steel fiber roughened and the cross section irregular. This goal can be achieved by using the melt pumping method. Because the steel fiber shrinks unevenly and becomes rough when it is rapidly cooled with air, and at the same time the cross section shrinks into a crescent shape, increasing the contact area with the substrate.

(2) Perform plastic processing on the fibers at a certain distance along the axis of the steel fiber.

(3) Shape the two ends of the steel fiber.

(4) Apply epoxy resin and surface micro-rusting treatment on the steel fiber surface. This method is not as good as the previous methods in improving the bonding strength of the interface, but it also has a certain enhancement effect.　

Tests by Kobayashi Kazusuke, University of Liège in Belgium, and Zhang Wengang have all proved that the reinforcing effect of steel fibers with hooks is approximately doubled than that of straight steel fibers. Kobayashi Kazusuke's experiments show that the effect of crimped steel fibers is close to that of hooks Steel fiber. These special-shaped steel fibers not only increase the strength of the steel fibers, but also increase the toughness. Although the corrugated steel fiber has little effect on improving the strength of steel fiber reinforced concrete, it can increase the toughness exponentially.

2. Hardness

No matter what kind of processing method is used, the steel fiber will encounter high heat and rapid cooling during the processing, which is equivalent to the quenched state. Therefore, the surface hardness of steel fibers is relatively high. When it is used for concrete reinforcement and mixing, the situation of bending rarely occurs. If the steel fiber is too hard or too brittle, it is also easy to break during stirring, which will affect the reinforcement effect. When the steel fiber is produced by the melt pumping method, the steel fiber ejected from the melt pumping wheel centrifugally is still in a high temperature state, and it must be dispersed and cooled by a roller or vibration conveying method. Otherwise, the steel fibers will accumulate and the heat will be difficult to dissipate, which will have an annealing effect.

3. Corrosion resistance

From the introduction of the corrosion resistance test of steel fiber reinforced concrete, it is known that when the cracked steel fiber reinforced concrete component is in a humid environment, the concrete at the crack is carbonized, and the steel fiber in the carbonized zone is corroded. The depth of carbonization and the degree of corrosion develop with time. For steel fiber reinforced concrete, the post-crack radian and post-crack toughness are mainly used. Although the crack width is smaller than that of the concrete, there are still cracks. Therefore, the steel fiber reinforced concrete used in humid environments, especially on the seashore, adopts anti-corrosion measures. Tests have proved that under the premise that steel fiber reinforced concrete components have the same load-bearing capacity, the use of steel fibers with a larger diameter can improve the corrosion resistance, and the use of epoxy resin or galvanized steel fibers will improve the corrosion resistance. If the construction process permits, this steel fiber can be used only on the surface of concrete within 1-2cm, and stainless steel fiber can also be used when necessary.