One: the purpose of conservation?
After concrete pouring, if the weather is hot and the air is dry, the water in the concrete evaporates too quickly, which leads to dehydration, so that the cement particles that have formed gel can not be fully hydrated, can not be transformed into stable crystals, and lack sufficient cohesive force, thus causing the concrete surface to fall off in flake or powder. In addition, when concrete does not have enough strength, premature evaporation of water will also produce large shrinkage deformation and dry shrinkage cracks, which will affect the durability and integrity of concrete. Therefore, the initial curing after concrete pouring is very important. Concrete should be cured immediately after final setting, and hard concrete should be cured immediately after pouring.
Two: maintenance methods?
The curing of concrete includes natural curing and steam curing. During the period of concrete curing, we should focus on strengthening the humidity and temperature control of concrete, minimize the exposure time of surface concrete, and cover the exposed surface of concrete closely (tarpaulin, plastic sheeting, etc.) in time. Can be used to cover) to prevent evaporation of surface moisture. Before the initial setting of the exposed surface protective layer concrete, the covering should be rolled up and rubbed with a trowel at least twice to make it smooth, and then covered. At this point, attention should be paid to the fact that the covering should not directly contact the concrete surface before the final setting of the concrete.
Three: maintenance requirements?
1) When concrete may come into contact with flowing water after form removal, effective heat preservation and moisture preservation measures should be taken before concrete comes into contact with flowing surface water or groundwater. The curing time should be extended (at least 14d) than the time specified in the above table, and the concrete strength should reach more than 75% of the design strength. After the maintenance, it shall be backfilled in time.
2) Concrete in direct contact with seawater or saline soil shall be protected from erosion before its strength reaches the design strength grade. And as far as possible to postpone the age of direct contact between fresh concrete and seawater or saline soil, generally not less than 6 weeks.
3) When the day and night average temperature is lower than 5℃ or the minimum temperature is lower than -3℃, it shall be treated as winter construction. When the ambient temperature is lower than 5℃, it is forbidden to spray water on the concrete surface for curing. At this time, curing liquid can be sprayed on the concrete surface, and appropriate insulation measures can be taken.
4) For concrete structures or members mixed with a large amount of fly ash in severely corrosive environment, after the specified curing period, if conditions permit, the wet curing time should be further appropriately extended on the basis of the above-mentioned curing measures.
5) During the curing period of concrete, the temperature of representative structures should be monitored, and the core temperature and surface temperature, environmental temperature, relative humidity, wind speed and other parameters of concrete should be measured regularly, and the curing system should be adjusted in time according to the changes of concrete temperature and environmental parameters, so as to strictly control the temperature difference inside and outside the concrete to meet the requirements.
6) During the concrete curing period, the concrete curing process shall be recorded in detail, and a strict post responsibility system shall be established.