Waterproof mechanism of polypropylene fiber concrete

The waterproof of polypropylene fiber concrete belongs to the rigid body waterproof of concrete. In the two ways of impermeability and crack resistance of waterproof concrete, polypropylene fiber mainly achieves the purpose of waterproofing by crack resistance. The mechanism of polypropylene fiber anti-cracking and waterproofing is based on the microscopic research on the consolidation and shrinkage of concrete.

From a micro perspective, any dense concrete has micro cracks. These microcracks exist between phases (phases of stone, sand, and cement colloids) and between cement microparticles, but normal microcracks are not visible to the naked eye. In the process of hardening and forming strength of concrete, the crystal and water should form crystals at the initial stage. The volume of this crystalline compound is smaller than the volume of the raw material, which leads to the shrinkage of the volume of concrete. Cause shrinkage. These stresses exceeded the tensile strength of the cement body for a certain period of time, thus causing micro cracks in the concrete. These micro-cracks inevitably exist at the local contact surface of the aggregate and cement gel in the concrete and inside the gel itself. In the process of concrete setting and hardening, micro-cracks have experienced the process of appearance and development. This process is considered macroscopically that concrete is shrinking during consolidation, and the shrinkage rate of general concrete is about 8 × 10-4. During the development of micro cracks in concrete, it develops from scratch to the weakest direction from small to large. Most of the development of micro cracks to fine cracks (about 70%) is completed within the gel period of 3-7 days. At this time, the tensile strength of concrete is less than 1Mpa. If effective anti-cracking measures are not taken, the inherent micro cracks in concrete Under the effect of internal and external stress, it will develop into larger cracks and eventually form through capillary channels and cracks, which will lead to waterproof failure, and also cause the structural design strength to be far from being fully exerted, which may even threaten the safety and use of the project.

The polypropylene fiber is mixed into the concrete. The polypropylene fiber and the cement aggregate have a strong binding force, which can be quickly and easily mixed with the concrete material and distributed evenly; at the same time, because of the fineness, the specific area is large, and the polypropylene fiber per kilogram The total length of the connection can be more than 10 times around the earth. If it is distributed in 1m3 of concrete, it can make nearly 20 fiber filaments per 1m3 of concrete, so it can form a uniform chaotic support system inside the concrete. When the micro-cracks are in the process of the development of the micro-cracks, they will inevitably encounter multiple micro-fibers in different directions. Because they are blocked by the fibers and consume energy, it is difficult to develop further. Therefore, polypropylene fiber can effectively suppress the occurrence and development of early dry shrinkage microcracking and segregation cracking of concrete, greatly reduce the shrinkage cracks of concrete, especially effectively suppress the generation of connected cracks. From a macro perspective, it is microfibers that disperse the directional tensile stress of concrete to achieve the effect of crack resistance. Tests show that, compared with ordinary concrete, the crack resistance of concrete with a volumetric content of polypropylene fibers of 0.05% (about 0.5 kg / m3) has increased by nearly 70%.

In addition, a large number of fibers that are evenly distributed in the concrete and adhere to each other play the role of "supporting" aggregate, which reduces the segregation of water and aggregate on the surface of the concrete, so that the diameter of the concrete is 50-100nm and greater than 100nm The pore content is greatly reduced, which can greatly improve the impermeability of concrete. Tests show that the polypropylene fiber with 0.05% volume content has improved the impermeability of ordinary concrete by 60% -70%.

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