1, steam method.
Steam curing of concrete can be divided into four stages: static stop, heating, constant temperature and cooling. Steam curing of concrete shall meet the following requirements respectively:
(1) During the static stop, the ambient temperature should be kept not lower than 5℃, and the temperature of concrete can only be raised after the pouring is completed for 4 ~ 6h.
(2) The heating rate should not be greater than 65438 00℃/h. ..
(3) At constant temperature, the internal temperature of concrete should not exceed 60℃, and the maximum temperature should not exceed 65℃. Constant temperature curing time should be determined by experiments according to the demoulding strength requirements of components, concrete mixture ratio and environmental conditions.
(4) The cooling rate should not be greater than 65438 00℃/h. ..
2, box girder steam curing method.
After concrete pouring, the beam body is sealed with a curing cover, and steam is input to control the humidity and temperature around the beam body.
When the temperature is low, input steam to raise the temperature, and after the initial setting of concrete, the bridge deck and the box are stored with water to keep moisture. The heating rate shall not exceed10℃/h; The constant temperature shall not exceed 45℃, the concrete core temperature shall not exceed 60℃, and the individual maximum temperature shall not exceed 65℃.
When cooling, the cooling speed shall not exceed10℃/h; When the temperature decreases to a point where the difference between the beam temperature and the ambient temperature does not exceed 15℃, remove the curing cover. The cooling of box girder cavity is slow, so ventilation measures can be taken appropriately. The temperature of all parts in the hood is consistent, and the temperature difference is not more than 65438 00℃.
3. Nature protection.
During the curing period of formwork concrete, measures such as formwork wrapping, watering and sprinkling should be taken to keep moisture and moisture, so as to ensure that formwork joints are not dehydrated and dry. In order to ensure the smooth form removal, the formwork can be loosened slightly after 24 ~ 48h of concrete pouring, and water conservation can be continued until the form removal, and then the moisture can be kept to the specified age.
Extended Information Cement Concrete Pavement Maintenance Cement concrete pavement can be divided into cast-in-place pavement and precast paving pavement according to its different construction methods. Common damages mainly include surface cracking, surface peeling and local extrusion.
The reasons are: insufficient subgrade strength, inappropriate slab thickness and vehicle load, poor concrete quality, improper setting of expansion joints, etc.
There are longitudinal cracks, transverse cracks, angular cracks and net cracks on the surface of the plate. In maintenance, asphalt is usually poured according to the crack width or filled with asphalt sand and asphalt mixture. Stripping and local crushing are generally filled with asphalt mixture.
For those seriously damaged and difficult to repair, sometimes a layer of asphalt pavement or cement concrete pavement will be added to the original pavement. For some seriously damaged plates, they are removed and poured again. Where precast blocks are laid, they can be removed and replaced.
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