Requirements for cement of concrete delivery pump

1. Reduce the friction resistance between the mechanical part of the concrete and the pump, the transmission pipeline and the concrete and have good fluidity.

2. Influence of cement variety on pumpability of concrete cement should have good water retention performance, so that the concrete is not easy to bleed during pumping. Ordinary silicochloric acid cement and pozzolanic cement have good water retention, while slag cement has poor water retention. If it is used to mix and pump concrete, it is necessary to increase the cement dosage, properly increase the sand rate or add a part of fly ash, and adopt a low slump. When using fly ash cement, the fluidity of concrete is good, but the early bleeding is large. It is appropriate to use low slump and pump continuously as much as possible.

3. The cement dosage shall be appropriate. If the cement dosage is insufficient, the pumping volume efficiency will be reduced, and the transportation resistance will be significantly increased. Moreover, the water retention of this concrete is very poor, and it is easy to bleed, segregate and block; If the cement dosage is too large, the concrete viscosity will be too large and the transportation resistance will be increased, but the pumping volume efficiency will not change much. Compared with gravel aggregate with the same particle size and gradation, the cement content of gravel concrete is larger. For fine aggregate, artificial crushed sand is more used than natural sand. The smaller the pipe diameter and the longer the pipe, the higher the fluidity, lubricity and water retention of the concrete, so the cement consumption should be increased. If the aggregate gradation is appropriate, the larger the maximum aggregate size is, the less cement will be used. However, when the aggregate size exceeds 30mm, the oversized aggregate will damage the continuity of the concrete, and it is difficult for the cement slurry to fully contain these aggregates, so the cement dosage cannot be reduced. The fine aggregate with a particle size less than 0.2 mm also plays a role similar to cement. However, these fine materials shall have a certain proportion. If the content is insufficient or the average particle size is too small, the cement consumption shall be increased. In case of pumping lightweight aggregate concrete, the cement consumption shall be appropriately increased. This is because the lightweight porous aggregate has the characteristics of absorbing water under high pressure and releasing water under reduced pressure, which is easy to make the concrete dry and hard and easy to segregate during pumping. Therefore, there should be more cement slurry in the lightweight aggregate concrete, and the cement dosage should not be less than 340kg / m3.