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In recent years, the synthesis technology of polycarboxylic acid mother liquor has become increasingly mature through several iterations, from the need to use purified water high-temperature esterification process to develop the tap water normal temperature method. Greatly reduces the threshold for the synthesis of polycarboxylic acid admixtures. Thanks to this, the performance of most mother liquors on the market is similar, providing a relatively common communication basis for compounding technology. At present, the raw materials of compound polycarboxylic acid admixtures can be roughly divided into the following categories: polycarboxylic acid mother liquor, retarder, defoamer, air-entraining agent, water retaining agent, antifreeze, and early strength agent. The types of various raw materials are complex and diverse, and the author holds the view of not looking at advertisements to see the efficacy. Emphasize on the types of more commonly used and convenient adaptation operations.

1. Mother liquor

The most common applications in a wide range of mother liquors are the water-reducing mother liquor and the slump-preserving mother liquor. Some people in the market are accustomed to call the slump-preserving mother liquor as a slump-preserving agent. The author believes that although the functionality of the slump-preserving mother liquor is very different from that of the water-reducing type, the synthesis method is only different from the synthetic raw materials. The so-called slump-preserving mother liquor is more standardized in the division of compound raw materials.

Perhaps readers will hear some opinions saying, "My water-reducing mother liquor is a comprehensive, slump-preserving, and highly water-reducing type." Basically, salespersons use words to promote their products. Compared with admixtures such as naphthalene-based additives, polycarboxylic acid admixtures do have slump retention and high water reduction effects. It's just the differences brought about by different objects of comparison. The polycarboxylic acid mother liquor can increase the water reduction rate by adjusting the ratio of acrylic acid to the macromonomer, but the slump retention performance of the mother liquor will be sacrificed. Under the game of increasing the water reduction rate, highlighting the cost-effectiveness, and improving the slump retention performance to ensure the use effect, the performance of the water-reducing mother liquor on the market is basically the same.

There are more types of slump-preserving mother liquor. 1. Synthesized by replacing HPEG with TPEG macromonomer; 2. Synthesized with HPEG monomer by replacing part of acrylic acid with hydroxyethyl acrylate; 3. Synthesized by TPEG monomer + hydroxyethyl acrylate. These will be introduced one by one in future articles. The author prefers to use the initial slump-preserving mother liquor without water reducing effect. This can easily measure the ratio of water-reducing mother liquor and slump-preserving mother liquor during the compounding process. The use of slump-preserving mother liquor is a cost-intensive process. The higher the requirements for the slump-preserving effect of concrete, the greater the amount of slump-preserving mother liquor. On the premise of ensuring the slump retention performance of concrete, reduce the amount of slump retention mother liquid as much as possible.

2. Retarder

Sodium Gluconate : It is cheap and can provide a certain water reduction rate. The most cost-effective, it is the most common retarder in compounding. The disadvantage is that there is a certain probability to reduce the workability of concrete.

White sugar: The price is slightly more expensive, the retarding effect is obvious, and the workability of concrete can be improved. The disadvantage is to increase the final setting time of concrete at low temperature.

Maltodextrin: The price is similar to that of sodium gluconate, which can improve the water retention of concrete. The disadvantage is that it may increase the loss of concrete slump.

In the compounding of commercial concrete, the combination of the above three retarders is the most commonly used method. In addition, there are sodium citrate, sodium tripolyphosphate and so on.

3.defoamer air-entraining agent

A certain amount of air-entraining agent in concrete is very beneficial to improve the fluidity, workability and pumpability of concrete, reduce the segregation and bleeding of the mixture, and improve the uniformity and durability of concrete. However, the amount of air-entraining agent should not be too high. Excessive air content will increase the compressibility of the air and produce an unsaturated state, which will increase the pump pressure loss during pumping. In the process of admixture renewal and iteration, the types of air-entraining agent defoamers are even more complicated than the mother liquor. The author prefers to use Evonik's ether defoamers and ether air-entraining agents. The price is slightly more expensive, but the better is the low dosage. In the admixture, only a few ten thousandths of the blending amount. The defoamer is to reduce the air content of concrete and eliminate large bubbles that are not conducive to concrete. The dosage is generally less than three ten thousandths.

4.water retention agent

When the workability of concrete cannot be completely improved by the above raw materials, water-retaining agents such as cellulose ether, polyacrylamide, and rubber can be considered to improve the workability of concrete. In commercial concrete, there are few applications of water-retaining agents. Too much water retaining agent will affect the slump retaining effect of concrete. Influencing the slump retention effect is to increase the compounding cost of the admixture in a disguised form. The amount of cellulose ether is less than three ten thousandths.

5.antifreeze early strength agent

Various inorganic salts have antifreeze effects. Commonly used antifreeze agents are sodium nitrite, sodium nitrate, calcium nitrate and so on. Sodium chloride has the lowest price, and chloride ions have the side effect of corroding steel bars. In order to reduce the compounding cost of admixtures, some admixture manufacturers combine sodium nitrite and sodium chloride with rust inhibiting effect. Antifreeze also has an early-strength effect. In addition, triethanolamine can be used to improve the early strength of concrete. Only the cost is also touching.

The above raw materials can basically meet the application of admixtures in commercial concrete. For detailed introduction, please refer to the literature. This article is just an introduction. Table 1 is a common combination in the formulation of admixtures. The ratio and type of each material can be adjusted according to the actual situation.

The introduction of these common raw materials does not mean that other raw materials are not suitable for concrete applications. Due to different regions, the effects of various raw materials will vary to a certain extent. It is also the responsibility of technicians to find out more suitable raw materials for local concrete applications.