Plastic shrinkage crack phenomenon:
On the surface of the structure, the shape is irregular and the length is not consistent, similar to dry mud surface. Most of them occur in the early stage of concrete pouring (about 4h after pouring), when the temperature of concrete itself is very different from that of the outside world, or its temperature is too high for a long time (more than 400) and the climate is very dry. Plastic crack, also known as cracking, strictly belongs to dry shrinkage crack, appear very common.
Reasons:
➤ After concrete pouring, the surface of concrete is not covered in time, and due to wind and sun exposure, the free water on the surface evaporates too fast, resulting in sharp volume shrinkage. In this case, the concrete has low strength at the early stage and cannot resist the deformation stress, resulting in cracking.
➤ Use cement with high shrinkage, excessive use of cement or excessive use of silt;
➤ The concrete water-cement ratio is too high and the formwork is too dry.
Prevention:
When making concrete, it should strictly control the water-cement ratio and the amount of cement, select well-graded stones, and reduce the porosity and sand ratio to vibrate and compact, so as to reduce shrinkage and improve the cracking strength of concrete.
➤ Wet the base and formwork before concreting;
➤ In the case of high temperature, low temperature or high wind speed, after concrete pouring, water should be sprayed for maintenance in time to keep it wet. In the first stage of maintenance, surface pressing and maintenance should be strengthened.
➤ The concrete can be maintained by spraying chlorine partial emulsion on the surface, or by covering straw bags or plastic films. When micro-cracks are found on the surface, it should be pressed in time and then covered and maintained.
➤ Wind protection facilities.
