1 。 introduce
The change of three-dimensional volume occurs in fresh concrete, mainly due to the rapid loss of blood evaporation on the surface. This leads to the rapid reduction of pore water level and the increase of pore water pressure, which often makes the surrounding solid particles close to all this, leading to the shrinkage of cement paste; The final constraint provided by the total amount leads to the cracking of fresh concrete on the surface. Plastic shrinkage cracks are usually observed in thin concrete with high specific surface area to volume ratio. In high performance concrete, with the addition of low water-cement ratio and silica fume, fresh concrete is more prone to plastic shrinkage cracks due to the formation of tiny pores and the decrease of bleeding rate, especially in hot, windy and dry weather conditions. When the evaporation rate is significantly higher than the bleeding rate, it will lead to the development of high tensile stress. Crete said that the surface area of capillary pores may be enough to exceed the tensile strength of concrete, especially in the early stage. If surface cracks appear, because plastic shrinkage is still ignored, they will become channels for external deterioration of the medium and reduce long-term durability.
Preventing plastic shrinkage cracks includes preventing rapid drying of concrete surface and good maintenance measures. In addition to these, the use of fiber as a second reinforcement mechanism can help develop light emphasis after drying. It is reported that the addition of metal fiber can not only control shrinkage cracks, but also provide sufficient tensile strength for concrete. In addition, in addition to non-metallic fibers, such as polypropylene, glass, polyethylene, etc., there are also reports of reducing the shrinkage crack width of concrete in later generations.