High-performance concrete air-entraining agent is used to prepare concrete retardant water-reducing agent and pumping agent. This product has small dosage, good performance, high water reduction rate, little impact on concrete strength, and small loss of concrete slump over time. It is the best choice to replace commonly used air-entraining agents such as rosin thermopolymer and sodium lauryl sulfate. At present, tens of thousands of tons of products have been used in concrete projects in various places, with significant technical and economic benefits. Its use can improve the durability of concrete and improve its frost resistance, impermeability and carbonation resistance, and is increasingly valued. Especially in northern areas, in order to improve the frost resistance of concrete, admixtures are mostly needed, of which air-entraining agents are one of the necessary ingredients.
Air-entraining agents all have water-reducing effects. Since they significantly change the workability, adding air-entraining agents under the same workability can reduce water consumption and reduce the bleeding rate by 50- 25%, significantly reducing settlement. This can also more or less reduce the loss of compressive strength caused by some air-entraining agents. Through the analysis of the effects of different types on concrete water reduction rate, air content and change in air content over time, compressive strength ratio and frost resistance, we try to provide a basis for everyone's selection and application.
Various air-entraining agents have certain differences in the performance of concrete, and the differences are as follows:
1. Compressive strength ratio. For air-entraining agents other than sodium lignosulfonate, when the air content is less than 3%, the compressive strength ratio will increase; when the air content is between 3% and 5%, for every 1% increase in air content, the compressive strength ratio will decrease by 1%. ~3%; when the air content is between 5% and 8%, for every 1% increase in air content, the compressive strength ratio decreases by 4% to 6%.
2. Frost resistance. Under the same air content conditions, the frost resistance of concrete from low to high is: sodium lignin sulfonate, sodium dodecyl sulfonate, polyether polyols, modified rosin thermopolymer, and triterpene saponin.
3. Water reduction rate. Within the reasonable scope of application, sodium dodecylbenzene sulfonate has basically no water reduction rate, followed by polyether polyols, and other varieties have water reduction rates that meet standard requirements when reaching a certain dosage.
4. Gas content. Under the same gas content, the dosages from small to large are: sodium dodecyl sulfonate, polyether polyols, modified rosin thermopolymer, triterpene saponin, and sodium lignosulfonate; the gas content is 1 hour. The temporal changes from small to large are: sodium lignin sulfonate, sodium dodecyl sulfonate, polyether polyols, modified rosin thermopolymer, and triterpene saponins.
The effect of air-entraining agents on concrete admixtures
(1) Air-entraining amount and bubble distribution
After adding air-entraining agents, air-entraining agents will be introduced during concrete mixing Lots of tiny bubbles. However, the amount of air entraining is not a fixed value for any kind of air entraining agent, and is generally between 3% and 5%. At the same time, concrete mixed with air-entraining agents contains hundreds of billions of bubbles per cubic meter, and the bubble diameters are mostly 20 to 200pm. In order to quantitatively express the shape of bubbles introduced by air-entraining agents, the bubble diameter size distribution, bubble specific surface area and spacing are used Coefficients and other parameters are described. Generally speaking, the bubbles are small, the specific surface area is large, and the spacing coefficient is small.
(2) Workability
The air-entraining agent introduces a large number of tiny and independent bubbles into the concrete. These spherical bubbles act as lubrication and ball bearings, making the concrete easy to work. The properties are improved, especially for gravel, extra-fine sand, and artificial sand concrete with poor aggregate shape.
(3) Bleeding and settlement shrinkage
After air-entraining agent is added to the concrete, due to the introduction of a large number of bubbles, the surface area of the entire system is greatly increased, which is higher than that without air-entraining agent. The viscosity is much higher when the agent is used, and bleeding and settling are therefore reduced. On the other hand, due to the existence of bubbles, the capillary channel of bleeding water is destroyed, and the migration of gas in the bubbles and the redistribution of bubbles can further destroy this channel; when ionic surfactants are used, the viscosity of the cement slurry further increases , all of which significantly reduce the bleeding and settlement of concrete after air entrainment.
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