After the concrete is poured and formed, it should be watered and covered in time for moisturizing maintenance to ensure that the concrete surface maintains a certain moist state. At the same time, in order to prevent the rapid and rapid evaporation of water, the surface should also be covered with covering materials such as plastic film, sacks or straw bags.
The concrete curing plan should be formulated according to factors such as site conditions, environmental temperature and humidity, structural parts, components or products, raw materials, and requirements for concrete performance. Water conservation, covering and moisturizing conservation, brushing conservation agent conservation, winter heat storage conservation and other methods. During construction, when formulating a maintenance plan, it often occurs in the entire construction process, and only a single maintenance method is used, and for the convenience of the drawing, water spray maintenance is mainly used. In order to ensure the realization of concrete performance, the curing method should be reasonably selected according to different structural parts.
(1) The exposed surface of the foundation mass concrete shall be covered and maintained.
It is more convenient to use watering curing method for the exposed surface of foundation mass concrete, but it is difficult to meet the frequency of watering curing in actual construction, which is easy to cause interruption of curing at night. To maintain a suitable temperature gradient inside and outside the concrete, uninterrupted 24h curing is essential.
According to past construction experience, the use of forced or uneven cooling measures during the maintenance of mass concrete is not only relatively expensive, but also easy to cause penetrating cracks in mass concrete due to poor management. Such methods are rarely used in housing construction projects. It is easy to cause water accumulation in the foundation pit, which is unfavorable for backfilling. Therefore, it is advisable to cover and maintain the exposed surface of the foundation mass concrete.
(2) Specifications for the construction of concrete structures
After the basement bottom and the first floor of the upper structure of the first floor of the column, wall concrete with mold curing can be used to continue the maintenance of water spray curing, if necessary, can also be used to maintain the cover curing or spray curing agent curing; according to the test, the impermeability effect of different curing methods The order is: water conservation > watering with grass bags > coating conservation agent > natural conservation, so it is the most reasonable plan to use water storage conservation for the basement floor.
(3) Concrete of other parts of columns and walls can be cured by sprinkling
If necessary, cover curing or spray curing agent can also be used for curing; however, the main load-bearing structure of the column system should use the plastic wrap method as much as possible; the shear wall structure should preferably use the brushing curing agent method.
(4) Plane structure, it is advisable to use plastic film to cover moisture while pouring and forming
However, for the bathroom floor and roof plane, in order to achieve the best impermeability effect, if possible, water storage should be used for maintenance. A common problem in construction is that it is easy to ignore the maintenance of the bottom surface of the floor slab. After the floor bottom formwork is removed, some construction workers have done maintenance on the surface layer, and the bottom layer cannot be sprinkled or covered for maintenance. In the process, the maintenance after the floor bottom form is removed is often omitted intentionally or unintentionally, and the exposed concrete surface should be maintained according to the requirements, and no part should be left out. Therefore, after the floor bottom form is removed, a dense curing agent should be sprayed for maintenance.
3. Determination of curing temperature
During the curing of concrete, attention should be paid to taking thermal insulation measures to prevent the temperature of the concrete surface from changing drastically due to environmental factors (such as exposure to sunlight, sudden temperature drop, etc.). During curing, the temperature difference between the core and the surface, and between the surface and the environment should not exceed 20°C. A strict maintenance plan should be formulated before the construction of mass concrete, and the temperature difference between the inside and outside of the concrete should be controlled to meet the design requirements. After the concrete is demolded in winter and hot seasons, if the weather changes suddenly, appropriate thermal insulation (cold season) and heat insulation (summer) measures should be taken to prevent the concrete from generating excessive thermal stress.
4. Conservation humidity control
In addition to the cold shrinkage caused by the temperature drop, the shrinkage of concrete, under the action of cement hydration, the relative humidity inside the concrete decreases with the progress of cement hydration, which causes self-drying and reduces the volume of concrete, resulting in premature concrete. The shrinkage of concrete is significantly affected by the relative humidity of the environment. The concrete with a curing humidity of 70% has larger drying shrinkage at each age than the concrete with a curing humidity of 90%. The drying shrinkage rate of the 3d age is the former. 8.3 times that of the person. The lower the relative humidity of the environment, the greater the dry shrinkage value. The development law of the dry shrinkage value with age is fast development in the early stage, slow development in the later stage and gradually stable.
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