How to Change Poor Workability of Fresh Concrete

The working properties of fresh concrete include fluidity, cohesion, and water retention. Fluidity refers to the ability of the concrete mixture to flow and evenly and densely fill the formwork under its own weight or mechanical vibration. Cohesion refers to the certain cohesion between the constituent materials of the concrete mixture, which can avoid the phenomenon of delamination and segregation during the construction process. Water retention means that the concrete mixture has a certain water retention capacity, which can avoid bleeding in the construction process.

In the actual preparation process of concrete, on the one hand, for low-strength concrete, the amount of cementitious material is not high and the water glue is relatively large. In addition, the aggregate gradation of this type of concrete is usually poor, and the use of high range polycarboxylate superplasticizer powder is used for the preparation of this type of concrete, which is prone to segregation and bleeding mixture; On the other hand, high-strength concrete prepared by using lower-strength grade cement, increasing the amount of cementitious material, and reducing the water-binder ratio is prone to high concrete viscosity, poor fluidity of the mixture and slow flow rate. Therefore, if the viscosity of the concrete mixture is too low or too high, it will cause poor performance of the concrete and reduce the construction quality, which is extremely detrimental to the mechanical properties and durability of the concrete.

Reduce the viscosity of the concrete mixture

The biggest drawback of high-strength concrete in its workability is that the viscosity of its mixture is often too large, which is not conducive to the construction of high-strength concrete. More construction chemicals in Kingsun, welcome to contact us to get more details.

Viscosity reduction measures often taken in actual projects include the following:

(1) Use high-quality fly ash. High-quality fly ash contains a large number of small spherical glass substances, which can play a good ball effect, thereby reducing the viscosity of the mixture. The particle diameter of ultra-fine fly ash is about 2um, and it is combined with silica fume (particle diameter about 0.2pm), cement, ordinary particle size fly ash, slag powder, etc., to reduce the concrete mixture when preparing high-strength concrete and ultra-high-strength concrete Measures for better viscosity.

(2) Use the appropriate amount of air-entraining agent. The air-entraining agent can significantly increase the content of micro-bubbles in the concrete mixture. These micro-bubbles will occupy the space of free water in the slurry so that more free water exists between the particle gaps, and the lubricating effect of water is improved. At the same time, the introduced tiny bubbles can also play a good ball effect, thereby reducing the viscosity of the mixture.

(3) Development of viscosity-reducing PCE. At present, the mechanism of action of the viscosity-reducing PCE is not clear. Most of the explanation is that this type of PCE can reduce the binding of its hydrophilic group to the white water in the slurry so that more free water participates in the inter-particle During lubrication, it has the effect of reducing viscosity. However, many researchers questioned it, thinking that this type of PCE may increase the content of beneficial bubbles in the slurry, thereby reducing the viscosity of the mixture.

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