Two important messages can be seen from the purpose of maintenance: the first is to keep the concrete saturated. In fact, as long as the ambient temperature is below 100%, the concrete will lose water. As long as the concrete loses water, the concrete will not be in the saturated state, which will produce defects and make the concrete become an unstable system and produce cracks. The more water is lost, the more unstable the volume is, and the more likely cracks will occur. Our company believes that the purpose of curing is to keep the concrete saturated or saturated as much as possible. In order to ensure that the hydration of concrete continues until the space initially filled with water in the fresh cement slurry is filled with cement hydration products to the desired degree.
When the environmental humidity is more than 80%, even if there is not much water loss in concrete, there will be no visible cracks, but there are still pores formed by water loss channel. If the concrete continues to lose water under the action of environment after hardening, the possibility of concrete cracking in the middle and later stage is very high. Therefore, as long as the relative humidity of the environment is less than 100%, the concrete should be cured, and water loss should be prevented after pouring to prevent the formation of water loss defects. The second is that "the space initially filled with water is filled with cement hydration products to the required degree", which is the requirement of curing time.
(1) Maintenance measures of cast-in-place slab
It is a quick and labor-saving method to cover the cast-in-place slab with plastic film after vibrating and plastering. However, attention should be paid to its water loss prevention effect. The covering film shall be airtight and impermeable and relatively thick, and the film shall be pressed tightly to make it adhere to the concrete surface, so that the mixing water is difficult to evaporate. During the setting out construction, do not lift up all the membrane, but cut off the parts that hinder the setting out with a paper cutter, and keep the film on the concrete surface, which is conducive to the maintenance of concrete.
(2) Maintenance measures of shear wall
For shear wall structure, the bolts fixing the formwork can be loosened in 24h, so that the distance between concrete and formwork is 5mm. The temperature difference between water temperature and concrete should not exceed 15 ℃. The formwork shall be removed within 3-5 days to avoid the formwork removal during the concrete temperature peak. After the formwork is removed, a qualified curing fluid shall be applied immediately after the formwork is removed for moisturizing, and the temperature control shall be carried out to ensure that the temperature difference between the center of the concrete body and the surface layer as well as the temperature difference between the surface layer and the environment shall not be greater than 25 ℃, the cooling rate shall not exceed 2 ℃ / D, and the water shall be watered and maintained for more than 14 days.
(3) Column maintenance measures
For columns, after the formwork is removed, plastic film shall be wrapped or curing liquid shall be applied immediately to ensure no water loss on the concrete surface.
(4) Maintenance measures of mass concrete
There are two methods for the maintenance of mass concrete: the first is the membrane covering method, which covers the membrane immediately after the concrete surface is rubbed flat. Then, according to the temperature measurement, ensure that the difference between the center temperature and the surface temperature of the concrete bottom plate does not exceed 25 ℃. If the temperature difference exceeds 25 ℃, a layer of cotton felt should be covered on the film; if the temperature difference value is still greater than 25 ℃, another layer of cotton felt should be covered. When the temperature difference value is not more than 25 ℃, cotton felt can not be covered. The second method is the water storage method: after the initial setting of the concrete on the surface of the bottom plate, 120 brick walls are built with 1:2 cement mortar at the edge of the leakage of the bottom plate, two skin high, and then the brick joints are plastered with mortar; after the concrete on the surface of the bottom plate is finally set, warm water (≥ 25 ℃) that has been exposed to the sun or stored in the water tank for more than one day can be flushed into the slab surface. The water storage height on the bottom plate surface is 80-100 mm.
(5) Maintenance measures of pavement concrete
The pavement concrete should be constructed in the morning and evening, avoiding the high temperature period at noon, staggering strong wind, rainy days and other bad weather. After the completion of pouring, vibrating, compaction and surface finishing, the materials such as straw bags, hemp pieces and felt shall be covered immediately. After the final setting, the materials can be watered 2-3 hours to keep them moist and maintain for 14 days. The incision was performed within 24 hours.
In addition, summer is a rainy season, so we should always pay attention to the weather changes during construction and make early prediction before the heavy rain. In case of rain, cover the vibrated and non vibrated concrete with plastic film. When the concrete is vibrated and plastered, it is better to press the surrounding area a little higher to let the rainwater accumulate on the concrete surface.
