Steam supply begins after concrete pouring, and the total curing time is related to the project site, temperature and cement variety, which should be determined according to local conditions and experience.
According to the difference of steam pressure, it can be divided into:
1, atmospheric steam curing
2, pressureless steam curing
3, micro-pressure steam curing
4, high pressure steam curing
Pay attention to steam curing.
1. Steam pipes shall be laid longitudinally, and the beams and templates shall not be directly faced when pouring steam to avoid local high temperature; In winter, the steam injection pipe is wrapped with a special insulation sleeve to ensure the normal supply of steam (that is, it is made of tubular hard foam wrapped with silver recycled cloth).
2. The key to the success of steam curing is to control the heating and cooling process, especially in the cooling stage. Because the early compressive strength of concrete increases rapidly at high temperature, its tensile strength does not increase in the same proportion, and its strength is low.
If the cooling gradient is too large, it is easy to produce large temperature tensile stress in concrete structure, which will lead to cracks. It is very important to control the temperature difference during the heating and cooling stages. Cracks can be effectively avoided by improving steam curing conditions and strengthening steam curing monitoring to ensure the temperature gradient within the range of 10~ 15 degrees.
Extended data
Concrete curing methods and existing problems in winter
1, coal-fired steam curing
In this way, in the process of generating steam, a large number of harmful gases (carbon dioxide, sulfur dioxide, nitrogen oxides) and PM2.5 are produced at the same time. Some large prefabricated beam yards need to invest a lot of money to build steam boiler rooms and arrange steam transportation pipes along the pedestal of the beam yard. The long transportation distance of steam pipeline also directly leads to large heat loss along the way, and the steam maintenance process needs 24-hour uninterrupted shifts.
2, honeycomb briquette furnace heat storage maintenance
In this way, a number of small honeycomb briquette stoves are generally placed in the covered concrete, and the heat generated by the combustion of the coal stoves is used for heat storage and insulation, which has no effect on moisture retention. More carbon monoxide gas is generated during the combustion process, which will aggravate the carbonation of concrete after contacting with the concrete surface. The existence of carbon monoxide in the curing shed cover has great security risks for construction workers entering the interior.
3. Hot water maintenance in winter
This method generally burns water to a certain temperature and then sprays it on the concrete surface through electric heating, which has a certain effect of heat preservation and moisture retention. However, with the loss of water, the heat will be lost quickly, and some areas of the concrete surface may freeze when the temperature drops.
4, electric steam curing
This method produces steam by electric heating, which is pollution-free. However, it still needs manual control in the construction process, and whether to supply steam is judged by manually measuring the temperature and humidity of maintenance. Therefore, the maintenance quality has a great relationship with the responsibility of operators, especially the temperature measurement at night is difficult to implement, so it has great limitations.
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