Common methods of concrete curing
I. Nature protection
Definition: At natural temperature (higher than +50C), cover watering or plastic film curing is adopted.
1, covering soil and water conservation
(1) cover concrete with straw curtains, sacks, sawdust, etc. Water shall be kept moist within 3 ~ 12h after concrete pouring, and the concrete mixed with ordinary cement, portland cement and slag cement shall be cured for not less than 7d, and the concrete mixed with retarding admixture and impervious concrete shall be cured for not less than14d; ; When the temperature is above 15℃, water it at least once every 3 hours during the day and twice at night in the first 3 days after concrete pouring, and then water it about three times in the morning and evening. When the temperature is high or the climate is dry, the watering frequency should be appropriately increased.
(2) When the average temperature of the day is lower than 5 degrees Celsius, do not water it.
(3) For large-area structures such as floor slab and roof slab, water storage maintenance can be adopted; For water storage tanks and other projects, water injection can be used for maintenance after the internal model is removed; For underground foundation engineering, covering soil can be used for maintenance. (Watering and maintenance of precast members, covering and maintenance of foundation works)
2, plastic film moisture curing
The plastic film is used as the covering, so that the concrete is isolated from the air, the water is no longer evaporated, and the cement is hardened by hydration and condensation of water in the concrete. It improves the construction conditions, saves labor and water, and ensures the curing quality of concrete. Moisturizing curing can be divided into plastic sheet curing and spraying plastic film curing liquid curing. (Moisturizing maintenance of row piles and frame columns) When using plastic film cloth for maintenance, its outer surface should be tightly covered and wrapped, and the secondary builder should also protect the plastic cloth from condensation water.
Second, heat curing.
It accelerates the strength growth of concrete by heating it. There are many methods of heating curing, including steam curing, hot film curing and solar curing (greenhouse, steam curing, pressurized steam curing, dry and humid heat curing).
1, steam curing
Under normal pressure, the steam temperature is about 45 degrees (which belongs to the requirements of construction speed or external conditions), and the pressure 1 standard atmospheric pressure; Steam curing can improve the 28d strength10 ~ 40% of cement mixed with admixture; P ⅰ, P ⅱ and P 0 decreased 10 ~ 15%. The purpose of steam curing is to speed up the exertion of concrete strength and meet the requirements of speeding up the construction progress, and the construction is not affected by the external environmental temperature.
2, pressurized steam curing
Pressurized steam curing method: in order to obtain high-strength concrete, the uncondensed concrete is directly pressurized by machinery, or placed in a high-pressure container, and the temperature is quickly raised under pressure for steam curing.
3. Warm shed method
Use thermal insulation materials to build a greenhouse, surround the whole assembly or structure, and ensure the high temperature in the greenhouse. A steam pipe can be installed in the greenhouse, or a furnace can be directly used to raise the temperature in the greenhouse.
4, dry wet heat curing
Wet saturated steam has high heat content, which can quickly heat and condense concrete products with high exothermic strength during wet and hot curing, and at the same time ensure the necessary humidity conditions for concrete hardening.
Third, the standard maintenance
The curing of concrete in wet environment or water with temperature of 20 degrees and relative humidity greater than 90% is called standard curing.
Fourth, electro-curing
The electrothermal infrared heater is used for radiation heating and curing of concrete, and is suitable for concrete heating at the joint of thin-walled reinforced concrete structure and assembled reinforced concrete structure.