What to pay attention to when using blast furnace slag

(1) When using ball mill slag powder, it is necessary to strengthen testing and strictly control the fineness of the slag powder. The fineness of slag powder in large vertical mills should be controlled between 400m2/kg and 500m2/kg. Due to its advanced production process, the fineness of slag powder is very stable. The fineness of ball milled slag powder is difficult to reach 400m2/kg, and it is difficult to maintain long-term stability. Once the fineness of blast furnace slag is significantly reduced, it will bring many problems to the concrete, such as bonding, segregation, and reduced bleeding; Extended setting time; Early strength may even decrease after 28 days.

(2) Attention should be paid to the content of slag powder. When adding blast furnace slag alone, it is advisable to use 30% to 40%, and the volume of concrete can be increased to over 50%, thereby significantly reducing the heat of hydration. The total replacement quantity shall not exceed 50%. Fly ash and slag powder should be controlled within 20% and 30% respectively. In the early stages of use, fly ash should be controlled within 10%, slag powder should be controlled within 20%, and large volume concrete should be relaxed.

(3) When compounding, choose the appropriate composite ratio for different grades of fly ash.

(4) Pay attention to the maintenance of concrete with slag powder (or a combination of slag powder and fly ash).

(5) Pay attention to adjusting the setting time of concrete. Compared with ordinary slag free concrete, the setting time of slag concrete has a certain retarding effect. The initial and final setting time of concrete is 1-2.5 hours later than that of the reference concrete. Therefore, commercial concrete enterprises should pay attention to adjusting the setting time of concrete, especially during winter construction, adjusting the concrete mix proportion, controlling the content of slag powder in the concrete, and using early strength water reducing agents. In summer, the addition of blast furnace slag can be increased to delay the setting time of concrete.