What are the requirements for fine stone concrete pumping for cement?
Requirements for Cement Conveyed by Fine Stone Concrete Pump
1. Reduce the frictional resistance of the mechanical part of the concrete with the pump, the conveying pipeline and the interior of the concrete and have good fluidity.
2. The influence of cement varieties on the pumpability of concrete The cement should have good water retention properties, so that the concrete is not easy to bleed during the pumping process. Ordinary Portland cement and pozzolan 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 amount of cement, appropriately increase the sand rate or add a part of fly ash. Low slump. When fly ash cement is used, the fluidity of the concrete is good, but the early bleeding is large, so it is advisable to use a lower slump and pump it as continuously as possible.
3. The amount of cement The amount of cement should be appropriate. If the amount of cement is insufficient, the pumping volumetric efficiency will decrease, and the conveying resistance will increase significantly, and the concrete has poor water retention, which is prone to bleeding, segregation and blockage; large, but the pumping volumetric efficiency does not change much. Compared with the crushed stone aggregate with the same particle size and gradation, the cement dosage of crushed stone concrete is larger. For fine aggregate, artificial crushed sand is more cement than natural sand. The smaller the pipe diameter and the longer the pipe, the higher the fluidity, lubricity and water retention of the concrete are required, so the amount of cement should be increased. If the aggregate gradation is appropriate, the larger the particle size of the large aggregate, the less the amount of cement. However, when the aggregate size exceeds 30 mm, the super-diameter aggregate will destroy the continuity of the concrete, and it is difficult for the cement slurry to fully absorb these aggregates.
Inclusive, so the amount of cement can no longer be reduced. Fine aggregates with a particle size of less than 0.2 mm also act like cement. However, these fine materials must have a certain proportion. If their content is insufficient, or the average particle size is too small, the amount of cement should be increased. If pumping lightweight aggregate concrete, the cement dosage should 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, and it 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 amount of cement should not be less than 340kg/m3.