Polyvinyl alcohol (PVA) fiber is a fiber with high modulus of elasticity, high tensile strength and high alkali resistance, and has been widely used in cement-based reinforcements. The research indicates that PVA fiber has good dispersibility in cement concrete, can significantly improve the flexural strength and toughness of concrete, and can limit the development of cracks and improve the crack resistance of concrete.
The mechanical properties of concrete are the basis for the application of concrete in buildings and structures. The incorporation of fibers and the improvement of mechanical properties are important indicators for evaluating fiber reinforcement. The current impact on the theory of fiber reinforcement mechanisms.
The most far-reaching is: the fiber spacing theory proposed by RomualDi in the United States and the composite material theory proposed by Swamy in the United Kingdom. From the point of view of fracture mechanics, it is believed that when the spacing of fibers in concrete is less than a certain value, the fiber acts as a crack-blocking effect on the cracks in the concrete, reducing the original defects in the concrete and improving its tensile strength. The composite material theory regards the fiber as the strengthening system of the concrete. From the mixing principle of the composite material, the performance of the fiber composite reinforcement material is not simply the effect of the composite phase "1+1=2". It is a weighted sum of matrix properties and fiber properties. Other related theories can be seen as based on these two theories, after comprehensive, perfect, and expanded.
Combined with basic theory and related research, it can be found that fiber is added to concrete mainly in three aspects:
(1) As a part of the composite, the fiber is co-stressed with the concrete matrix and bears part of the stress. (2) The three-dimensional disorder of the fibers is distributed in the concrete, which effectively suppresses and reduces the generation and development of the initial cracks in the cement matrix, and to some extent compensates for the defects inside the concrete.
(3) When the concrete is deformed by force, the fiber can effectively restrain its deformation, and the plasticity of the concrete can be improved.
When the crack is generated and expanded, due to the "bridge" effect of the fiber, the fiber itself can be forced across the crack, and the friction between the fiber and the substrate consumes energy, so the ductility of the material is increased.