What is PVA fiber?
As a new synthetic fiber with high tensile strength and high elastic modulus, polyvinyl alcohol (PVA) fiber has a broad application prospect in improving crack resistance and bending toughness of concrete. High-strength high-performance concrete is increasingly used in large-scale water conservancy and hydropower projects, Bridges, railways, ports, high-rise buildings, subways and tunnels. Using high strength high performance concrete can optimize the structural design, improve the space utilization rate and speed up the construction speed, but the shrinkage and brittleness of high performance concrete restrict its application and development. The higher the strength of concrete is, the lower the tension/compression ratio of concrete is; the more brittle concrete is, and the more prone to cracking is. Therefore, higher requirements are put forward for improving the crack resistance and bending toughness of concrete. PVA fiber is the key material to realize the ultra-ductility of engineering cement-based material (ECC). However, there is still a lack of systematic research on the experimental research and engineering application of adding PVA fiber with high strength and elastic modulus to improve the crack resistance and bending toughness of concrete.
What are the properties and characteristics of PVA fiber?
Such concrete fiber additive is used for concrete crack resistance, which is commonly used in the equivalent diameter of 5 ~ 20 microns, tensile strength of about 1 100 MPa. The elastic modulus is less than 35 GPa of medium strength and modulus of chopped PVA fiber, which can also use high strength and high elastic modulus of chopped PVA fiber. PVA fiber with high strength and elastic modulus has the same high tensile strength as steel bar, and its elastic modulus is greater than or equal to 35 GPa, which is close to the elastic modulus of concrete, and can significantly improve the toughness or ductility of concrete.
PVA fiber is distributed evenly in concrete, and is distributed in random directions and overlapped into a three-dimensional network structure. It plays a role in improving crack resistance and toughness in concrete, so as to improve the overall quality and durability of concrete. After adding PVA fiber into concrete, it will not have chemical reaction with any material in concrete, and its physical and chemical properties are stable. The role of PVA fiber in crack resistance and toughening in concrete is purely physical, and it is a new material that can improve the crack resistance and toughness of concrete.
The uniform dispersion degree of PVA fiber concrete is an important premise to exert its anti-crack and toughening effect in concrete. For the concrete with high content of PVA fiber, the uniform dispersion of PVA fiber has a more significant impact on the crack resistance and toughening effect of concrete. Cutting PVA fiber with high strength and elastic modulus is adopted in relevant studies. When the fiber volume content is increased to 2%, the uniform dispersion of the fiber can still be guaranteed, and the crack resistance and toughness of concrete can be significantly improved. But with high content of medium strength and elastic modulus of superfine short cut of PVA fiber concrete, when in actual use, prone to cluster in the fiber in the concrete or scattered unevenly, need through the optimization of fresh concrete and plastic viscosity and improve PVA fiber surface hydrophilicity and other measures to improve the uniformity of dispersion of ultrafine PVA fiber in the concrete characteristics, to ensure its role in the crack resistance of concrete.