Post Date:23,Sep,2024
1)Admixture
The dosage of admixture is small (0.005%-5% of the cement mass) and the effect is good. It must be calculated accurately and the weighing error should not exceed 2%. The type and dosage of admixtures must be determined through experiments based on factors such as concrete performance requirements, construction and climate conditions, concrete raw materials and mix ratios. When used in the form of a solution, the amount of water in the solution should be included in the total amount of mixing water.
When the combined use of two or more additives causes flocculation or precipitation of the solution, the solutions should be prepared separately and added to the mixer respectively.
(2) Water reducing agent
In order to ensure uniform mixing, the water-reducing agent should be added in the form of a solution, and the amount can be increased appropriately as the temperature rises. The water-reducing agent should be added to the mixer at the same time as the mixing water. When transporting concrete with a mixer truck, the water-reducing agent can be added before unloading, and the material is discharged after stirring for 60-120 seconds. Ordinary water-reducing admixtures are suitable for concrete construction when the daily minimum temperature is above 5℃. When the daily minimum temperature is below 5℃, they must be used in combination with early-strength admixtures. When using, pay attention to vibrating and degassing. Concrete mixed with water-reducing agent should be strengthened in the initial stage of curing. During steam curing, it must reach a certain strength before it can be heated. Many high-efficiency water-reducing agents have a large slump loss when used in concrete. The loss can be 30%-50% in 30 minutes, so care should be taken during use.
(3) Air-entraining agent and air-entraining water-reducing agent
Concrete with high freeze-thaw resistance requirements must be mixed with air-entraining agents or water-reducing agents. Prestressed concrete and steam-cured concrete should not use air-entraining agents. The air-entraining agent should be added in the form of a solution, first added to the mixing water. Air-entraining agent can be used in combination with water-reducing agent, early strength agent, retardant, and antifreeze. The prepared solution must be fully dissolved. If there is flocculation or precipitation, it should be heated to dissolve it. Concrete with air-entraining agent must be mechanically mixed, and the mixing time should be greater than 3 minutes and less than 5 minutes. The time from discharging to pouring should be shortened as much as possible, and the vibration time should not exceed 20 seconds to avoid loss of air content.
(4) Retardant and retarding water reducing agent
It should be added in the form of a solution. When there are many insoluble or insoluble substances, it should be fully stirred evenly before use. The stirring time can be extended by 1-2 minutes. It can be used in combination with other admixtures. It must be watered and cured after the concrete has finally set. Retarder should not be used in concrete construction where the daily minimum temperature is below 5℃, nor should it be used alone for concrete and steam-cured concrete with early strength requirements.
Post time: Sep-23-2024
