The basic properties of steel fiber reinforced concrete
The basic properties of steel fiber reinforced concrete
Steel fiber reinforced concrete is an excellent and wide application of new composite materials. As the steel fiber can play a role in blocking matrix cracks in concrete, making it significantly improve the tensile, flexural, shear strength than ordinary concrete, its impact resistance, fatigue resistance, toughness and durability after the split has greatly improved
1.The effect and influence factors of steel fiber for concrete
Disorderly distributed short steel fiber mainly block inner micro cracks in concrete to expand,so significantly improve the tensile strength, shear strength and flexural strength, when the dosage of steel fiber is within 1%-2%,the tensile strength is improved 25%~50%, the flexural strength is improved 40%-80% ,the shear strength is improved 50%-100% tested by directly shearing double sides. Compressive strength increased to a lesser extent, generally between 0 and 25%.
2. Fatigue Performance
Flexural and compressive fatigue properties of steel fiber reinforced concrete than ordinary concrete has greatly improved. For example: when flexural fatigue life of 106 times, the stress ratio of the steel fiber reinforcement concrete with the steel fiber dosage 1.5% (LF / DF = 58) is 0.68, but the ordinary concrete is only 0.51; when the stress ratio is 0.7, steel fiber reinforced concrete bending fatigue life is more than 105 times, and the normal concrete is only 850 times. Another example: when fiber dosage is 2%,the Concrete Life is 2X 106times, the stress ratio up to 0.92, and the stress ratio than ordinary concrete only up to 0.56. Visible in the pavement and machines to withstand the fatigue loading pier project, the use of steel fiber reinforced concrete will make it significantly improved fatigue life.
3. Tensile strength
In order to the steel fiber reinforced concrete with better mechanical properties, it requires a certain tensile strength for steel fiber. According to the different materials and production processes of steel fiber, its tensile strength is also somewhat different. Since ordinary steel fiber concrete is damaged is mainly due to the steel fiber pulled-out, not the steel fiber pulled off, and steel fibers during failure withstand the maximum tensile stress of 100 ~ 300MPA, therefore, as long as the tensile strength of steel fiber in 380MPA above, general can meet the requirements.
4. Elastic Modulus
Modulus of elasticity of steel fibers 200GPA, ultimate elongation of 0.5% to 3.5%.
5. Bond strength
Since the destruction of steel fiber reinforced concrete is mainly caused due to pull out of steel fiber, thus increasing steel fiber and concrete matrix interfacial bond strength is very important. Improving bond strength, the properties of the matrix is important, but except that, for the steel fiber itself, it should improve the steel surface shape to improve the bonding properties. Commonly used methods are: the steel fiber surface roughening, irregular cross-sectional shape, increasing the contact area with the substrate and friction; steel fiber surface indentation or pressed into a wave, to increase the mechanical bite force; steel fiber ends shaped-based, will be made at both ends of the hook or bulk form, etc., to improve their anchoring force or pullout force
6. Hardness
The surface hardness of various steel fibers is higher, because when stirred the concrete, bending phenomenon generally should not occur. But sometimes the steel fiber material is relatively brittle, easily broken while stirring, affecting the enhancement. Therefore, the actual production applications to always observe a dispersion of rows of steel fibers, steel fibers dispersed after stirring should be stopped.
7. Corrosion resistance
The chemical resistance of steel fiber reinforced concrete is problem that people are most concerned about. In this regard, experts and scholars have done a lot of tests and field exposure, almost reached the same conclusion: steel fiber reinforced concrete in the air, waste water and sea water are showing good corrosion resistance. 5 years after the specimen exposure to sea water,its carbonation depth is less than 5MM, only the surface layer of steel fibers produce rust, steel fibers inside are not corroded, unlike ordinary reinforced concrete after corrosion, corrosion layer of concrete after volume expansion make the concrete crack. Specialized research showed that: after 300 cycles sea water immersion (dip 12H, air dry 12H), steel fiber concrete chloride ion immersion depth smaller than ordinary concrete, although more than 0.4% of the chloride ion activation volume, but no steel fiber corrosion. The steel fiber pouring inside the concrete, as long as the tamping compacting, and air separation, steel fibers are generally not corrosion phenomenon. Exposed concrete surface or when the crack width over 0.25MM, spanning cracks easily corroded steel fibers.