Post Date:5,Feb,2024
Selection of concrete admixtures:
(1) Efficient and high-performance water-reducing agent: Since the fluidity of concrete is mainly adjusted by high-efficiency water-reducing agent, the dosage accounts for 1% to 2% of the weight of cement; for concrete with special requirements for early strength, use quick-setting cement or Add silica fume; when using silica fume for concrete that requires wear resistance, and when large-volume high-strength concrete needs to limit the heat of hydration, the amount of cement must be reduced and silica fume or fly ash must be added. The initial setting time of concrete mixed with high-performance water-reducing agent is longer than that of ordinary concrete. The greater the amount, the longer the initial setting time.
(2) Air-entraining agent and air-entraining water-reducing agent: It is required to have high frost resistance and high density, and must be mixed with air-entraining agent or air-entraining water-reducing agent. Add a certain amount of air content to concrete, and if the air content increases by 1%, the strength will decrease by about 5%. Therefore, when preparing high-strength grade concrete, the air content should be about 3%, and air-entraining agents should be used with caution. However, the use of air-entraining agents has more advantages than disadvantages on the performance of concrete such as anti-freeze and anti-permeability.
(3) Antifreeze selection: When applying high-strength concrete in winter, first select an antifreeze that is suitable for the ambient temperature expected during pouring. During construction, a compound antifreeze with water-reducing, air-entraining, anti-freezing and early-strength components is used. The main function of the composite early-strength antifreeze is to reduce the mixing water consumption and significantly reduce the excess free water in cement hydration, thus reducing the amount of freezing. The composite air-entraining agent generates a large number of closed micro-bubbles in the fresh concrete, which alleviates the volume expansion force of freezing on the concrete, lowers the freezing point, and allows the concrete to continue to hydrate at negative temperatures. The early-strength component in the air-entraining agent accelerates the hydration of the mixture and strengthens it early, meeting the critical strength as early as possible and avoiding early freezing damage. Nitrates, nitrites and carbonates are antifreeze components and are not suitable for galvanizing and reinforced concrete admixtures. Concrete for drinking water and food engineering shall not use antifreeze components containing chromium salt early strength agent, nitrite and nitrate. Antifreeze containing urea components should not be used in residential buildings and commercial buildings.
Post time: Feb-06-2024