Post Date:30,Sep,2024
(5) Early strength agent and early strength water reducing agent
Some are added directly as dry powders, while others should be mixed into solutions and used according to the instructions for use. If it is mixed in the form of dry powder, it should be dry-mixed with cement and aggregate first, then add water, and the mixing time should not be less than 3 minutes. If used as a solution, hot water at 40-70°C can be used to accelerate dissolution. After pouring, it should be covered with plastic film for curing. In low-temperature environments, it should be covered with insulation material. After final setting, it should be watered and moisturized immediately for curing. When steam curing is used for concrete mixed with early strength agent, the steam curing system must be determined through experiments.
(6) Antifreeze
Antifreeze has specified temperatures of -5°C, -10°C, -15°C and other types. When using it, it should be selected according to the lowest daily temperature. Concrete mixed with antifreeze should use Portland cement or ordinary Portland cement with a strength grade of not less than 42.5MPa. The use of high alumina cement is strictly prohibited. Chloride, nitrite and nitrate antifreezes are strictly prohibited from being used in prestressed concrete projects. Concrete raw materials must be heated and used, and the mixer outlet temperature must not be lower than 10°C; the amount of antifreeze and the water-cement ratio must be strictly controlled; the mixing time should be 50% longer than normal temperature mixing. After pouring, it should be covered with plastic film and insulation materials, and no watering should be allowed during maintenance at negative temperatures.
(7)Expanding agent
Before construction, a trial mix should be carried out to determine the dosage and ensure an accurate expansion rate. Mechanical mixing should be used, the mixing time should not be less than 3 minutes, and the mixing time should be 30 seconds longer than that of concrete without admixtures. Shrinkage-compensating concrete should be mechanically vibrated to ensure compactness; mechanical vibration must not be used for filling expansion concrete with a slump above 150mm. Expansive concrete must be cured in a humid state for more than 14 days, and the latter must be cured by spraying a curing agent.
(8)Accelerating setting agent
When using accelerating setting agents, full attention should be paid to the adaptability to cement, and the dosage and usage conditions should be correctly grasped. If the content of C3A and C3S in cement is high, the concrete mixture of accelerator must be poured or sprayed within 20 minutes. After the concrete is formed, it must be moisturized and maintained to prevent drying and cracking.
Post time: Oct-09-2024
