introduce
The concrete construction of bridge engineering is greatly influenced by the construction conditions. Maintenance is an essential process of bridge engineering, and the correct bridge maintenance method is the key to the normal operation of the bridge. In order to keep the bridge in good condition after completion, it needs to be solved through maintenance, so as to achieve good operational purposes.
1, general requirements for concrete construction
1. 1, concrete construction in hot climate
The concrete temperature before pouring should not exceed 32℃. The Contractor shall take the following measures to keep the concrete temperature below 32℃:
(1) Masking or covering aggregate and other components and cooling. Cool the mixed water by freezing or burying water tank or adding crushed ice to some mixed water, but after mixing, all the ice should be melted.
(2) Before pouring concrete, the surfaces of formwork, steel bars, steel flanges, etc. in contact with concrete should be cooled to below 32℃.
(3) The concrete pouring temperature of bridge deck and bridge deck pavement shall not exceed 26℃. When the evaporation rate is greater than 0.5kg/m/h? 2, should not be on the bridge deck, bridge deck pavement or other exposed concrete slab structure.
1.2, concrete construction in winter
(1) When the daily average outdoor temperature is lower than 5℃ for five consecutive days, in addition to the materials and construction requirements, a winter construction plan shall be submitted, detailing the construction methods and equipment to ensure that the temperature is not lower than 10℃ for the first seven days after pouring.
(2) The contractor shall have enough thermometers that can record continuously, and record at intervals of about 30m for the first 7 days. (2) When pouring concrete, put a thermometer, and observe and record it continuously by special personnel.
(3) When mixing concrete, the temperature of each material should meet the temperature required for mixing. In order to meet the mixing temperature, the materials can be heated separately.
(4) When chloride is mixed into the heated mixture, the initial setting of concrete shall not be earlier than the end of concrete pouring, and steam curing shall not be used. When pouring concrete on hardened concrete, the temperature of the joint surface should be at least 5℃, and the temperature should be kept at or above 5℃ when pouring concrete. When mixing concrete, the mixing time should be extended by 50%.
(5) The contractor shall be responsible for protecting concrete in cold weather in winter. Any concrete damaged due to poor protection and freezing must be removed and poured again.
2. General requirements for concrete curing
(1) After the completion of concrete pouring, the surface should be cured as soon as possible after the slurry is collected, and the newly poured concrete surface exposed to the atmosphere should be watered in time or covered with wet sacks and wet cotton felt for curing. If conditions permit, water storage or sprinkler maintenance should be adopted as far as possible.
(2) For concrete with water-binder ratio lower than 0.45 and concrete with large fly ash content, when pouring large-area components, the exposed working face should be reduced as much as possible, and the exposed working face should be closely covered with plastic film immediately after pouring. After the final setting, the film can be removed for water conservation.
(3) In the process of plastering and screeding after concrete pouring, it is forbidden to sprinkle water on the concrete surface, and excessive operation should be prevented from affecting the quality of surface concrete.
(4) The pouring temperature of concrete should be adjusted according to the air temperature, which should not be higher than the air temperature and not more than 30℃ in hot climate and lower than 12℃ in low temperature. In the process of construction and maintenance, the midpoint temperature of key sections and the surface temperature about 5cm away from the surface are measured, and strict temperature control is implemented.
(5) When the ambient air temperature is lower than the surface temperature of the concrete being maintained by more than 20℃, the concrete surface must be covered with thermal insulation materials to reduce the cooling speed. Cast-in-place concrete should have enough moisture curing time.
(6) When the structure contacts flowing surface water or groundwater, waterproof measures should be taken to ensure that the concrete will not be washed away by water within 7 days after pouring.
(7) In addition to considering the strength of concrete during formwork removal, the temperature of concrete during formwork removal should not be too high to avoid cracking due to contact with air and cooling too fast. At this time, cold water curing is not allowed.
3, concrete construction and maintenance methods
3. 1, sprinkle water for health.
(1) Automatic sprinkler system and sprayer shall be used for sprinkler maintenance, and wet maintenance shall not be interrupted and dry-wet cycle shall not be formed. The covering materials provided shall be approved by the supervision engineer in advance.
(2) Sprinkling water for keeping in good health should be based on the temperature situation, and the appropriate time interval should be mastered to keep the surface moist during maintenance. When the temperature is lower than +5℃, it should be covered with heat preservation, and water should not be sprayed for health preservation.
3.2. Waterproof paper and sanitary plastic sheets.
(1) The waterproof paper should be as wide as possible.
(2) The use requirements of plastic sheets are the same as those of waterproof paper.
3.3, steam curing
(1) When the contractor adopts steam curing, it shall confirm in advance that the concrete members with additives have no harmful effects after steam curing through tests before steam curing.
(2) Steam curing shall be carried out in accordance with sections 1 1.8 and 14.2 of JTJ 04 122000 Technical Specification for Construction of Highway Bridges and Culverts.
(3) Formwork removal and steam curing should be selected to avoid concrete cracking.
(4) Components cured by steam shall not be watered for curing.
4. Conclusion
As can be seen from the above, concrete construction and concrete maintenance play a very important role in the process of bridge construction. The durability quality of concrete on structural surface depends largely on the humidity and temperature control during construction and maintenance. As a construction unit, we should pay attention to every link and complete the construction of each bridge on time with good quality and quantity.
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