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How to choose and use water reducing agents correctly and reasonably?
Blog How to choose and us
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Adding air entraining agents or air entraining water reducing agents introduces a large number of small, independent bubbles into concrete, which act like balls and greatly improve its workability. This effect is particularly significant in gravel or artificial sand concrete with poor aggregate particle size.
The improvement in the workability of fresh concrete by adding air-entraining agents or air-entraining water-reducing agents mainly manifests as increased slump and reduced bleeding and segregation.
If the slump remains unchanged, the water-cement ratio can be reduced by introducing air into the concrete. Therefore, adding air-entraining agents may also help reduce water content. Generally, for every 1% increase in the air content of concrete, while maintaining the same slump, the water-cement ratio can decrease by 2% -4% (reducing the unit water consumption by 4-6kg). If air-entraining and water-reducing agents are added, their combined effects of air entrainment and water reduction are highly beneficial in reducing the water-cement ratio of concrete.
The water reduction rate of air-entraining agents often varies due to differences in air-entraining volume, aggregate size and gradation, cement type and dosage, etc. But one thing is certain, that is, the larger the amount of air entraining agent added, the higher the air content in the concrete and the higher the water reduction rate. Although the water-reducing effect of air-entraining agents helps compensate for the negative effect of air entraining on strength, the air content of concrete should not be too high, or strength will decrease significantly.
The addition of air entraining agents or air-entraining water-reducing agents significantly reduces concrete bleeding and settlement.
Kreijger proposed a relationship between relative bleeding rate and admixture concentration through experiments. For cement slurry with W/C=0.50, the relative bleeding rate when adding an anionic water-reducing agent is:
Qx / Q = 1 – 10x
For those mixed with anionic air entraining agents and non-ionic water-reducing agents, the relative bleeding rate is:
Qx / Q = 1 – 4x
In the formula: Qx/Q – relative bleeding rate; Qx – bleeding rate of cement slurry without admixtures; Q – The bleeding rate of cement slurry mixed with additives; X – Concentration of admixture.
When using the same concentration of admixtures, the bleeding rate of concrete can be calculated from the bleeding rate of cement slurry.
The degree of bleeding and settling is closely related to the viscosity of the cement slurry in concrete, which, in turn, is related to the adsorption of air-entraining agents onto the particles and the adhesion of bubbles to the particle surface. Due to the presence of a large number of tiny bubbles, the surface area of the entire slurry system increases and the viscosity increases, inevitably leading to a reduction in bleeding and settling.
In addition, the presence and relative stability of a large number of tiny bubbles actually hinder the migration of moisture from the interior of concrete to the surface, blocking the channels for water seepage; Furthermore, due to adsorption, bubbles, cement particles, and aggregate surfaces all carry the same charge. As a result, bubbles, cement particles, and aggregates are in a relative “suspended” state, preventing heavy particles from settling and helping reduce bleeding and sedimentation.
The addition of air entraining agents greatly improves the uniformity of concrete by reducing settlement and bleeding, and reduces the possibility of water pockets forming under the aggregate. In addition, the combined use of air-entraining agents or air-entraining water-reducing agents is a technical guarantee for producing high-fluidity, self-leveling concrete.
How to choose and use water reducing agents correctly and reasonably?
Blog How to choose and us
