In recent years, the synthesis technology of polycarboxylate mother liquor has become increasingly mature through several updates and iterations. It has evolved from the high-temperature esterification process that requires pure water to the constant temperature method of tap water. Greatly reduces the synthesis threshold of polycarboxylate additives. Thanks to this, the vast majority of mother liquors in the market have similar performance, providing a relatively common communication foundation for compounding technology. The raw materials for compounding polycarboxylate admixtures can be roughly divided into the following categories: polycarboxylate mother liquor, retarder, defoamer and air entraining agent, water retaining agent, antifreeze agent, and early strength agent. The types of various raw materials are complex and diverse, and the author adheres to the viewpoint of focusing on actual effects without watching advertisements. Emphasize the commonly used and convenient types of adaptation operations.
1、 Mother liquor
The most commonly used types of mother liquor in various categories are water reducing mother liquor and slump retention mother liquor. Some people in the market commonly refer to slump retention mother liquor as a slump retention agent. The author believes that although there is a significant difference in functionality between slump retention mother liquor and water reducing mother liquor, the only difference in synthesis methods is the raw materials used. It is more standardized in the classification of composite raw materials, known as the collapse protection mother liquor.
Perhaps readers may hear some viewpoints that say, "My water reducing mother liquor is comprehensive, with a slump retention effect, and highly water reducing.". Basically, it's all the language used by salespeople to promote their products. Compared to additives such as naphthalene series, polycarboxylate admixtures do have the effects of slump retention and high water reduction. However, it is the difference caused by different comparison objects. Polycarboxylic acid mother liquor can increase its water reduction rate by adjusting the ratio of acrylic acid to macromonomers, but it will sacrifice the slump retention performance of the mother liquor. In the game between improving the water reduction rate, highlighting the cost-effectiveness, and improving the collapse resistance performance to ensure the effectiveness of use, the performance of water reducing mother liquor in the market is basically the same.
There will be more types of slump retention mother liquor. 1. Synthesized by replacing HPEG process with TPEG macromonomer; 2. It is synthesized by replacing a portion of acrylic acid with hydroxyethyl acrylate and using HPEG monomer; 3. Synthesized from TPEG monomer+hydroxyethyl acrylate. These will be introduced one by one in future articles. The author prefers to use a slump retention mother liquor that does not have an initial water reducing effect. This can easily measure the ratio of water reducing mother liquor to slump retention mother liquor during the compounding process. The use of slump retention mother liquor is a cost reducing process, and the higher the requirements for slump retention effect of concrete, the greater the amount of slump retention mother liquor used. On the premise of ensuring the slump retention performance of concrete, minimize the amount of slump retention mother liquor as much as possible.
2、 Retarder
Sodium gluconate: It is inexpensive and can provide a certain water reduction rate. It has the highest cost-effectiveness and is the most common retarder in compounding. The disadvantage is that there is a certain probability of reducing the workability of concrete.
Sugar: It is slightly expensive and has a significant retarding effect, which can improve the workability of concrete. The disadvantage is that it increases the final setting time of concrete at low temperatures.
Maltodextrin: Its 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 addition, there are also sodium citrate, sodium tripolyphosphate, and so on.
3、 Defoaming agent and air entraining agent
A certain amount of air entraining agent in concrete is beneficial for improving its fluidity, workability, pumpability, reducing segregation and bleeding of the mixture, and improving the uniformity and durability of the concrete. However, the amount of air entraining agent should not be too high. Excessive air content can increase the compressibility of the air, resulting in an unsaturated state and increasing pump pressure loss during pumping. In the process of updating and iterating additives, the types of air entraining and defoaming agents are even more complex than the mother liquor. I prefer to use ether based defoamers and ether based air entraining agents from Evonik in Germany. The price is slightly higher, but the advantage lies in the low usage. Only a few thousandths of the dosage in the admixture. Defoamers are used to reduce the air content of concrete and eliminate large air bubbles that are detrimental to the concrete. The dosage is generally below three in the ten thousand.
4、 Water retaining agent
When the workability of concrete cannot be completely improved by the above raw materials, water retaining agents such as cellulose ether, polyacrylamide, and warm wheel glue can be considered to improve the workability of concrete. In commercial concrete, the application of water retaining agents is rare. Excessive water retaining agent can affect the slump retention effect of concrete. The impact on the slump retention effect is a disguised increase in the cost of compounding additives. The dosage of cellulose ether is below 0.03%.
5、 Antifreeze early strength agent
Various inorganic salts have antifreeze effects, and commonly used antifreeze agents are sodium nitrite, sodium nitrate, calcium nitrate, etc. Sodium chloride has the lowest price, and chloride ions have the side effect of corroding steel bars. Some additive manufacturers, in order to reduce the cost of compounding additives, combine sodium nitrite and sodium chloride, which have rust inhibiting effects. Antifreeze agents also have early strengthening effects. Additionally, triethanolamine can be used to improve the early strength of concrete. However, the cost aspect 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 shows the common combinations in an additive formula, and the proportion and type of each material can be adjusted according to the actual situation.
Table 1
Water Reducing mother liquor | Slump retention mother liquor | Sodium gluconate | Air entraining agent |
Defoamer |
cellulose |
water |
18% | 2% | 2% | 0.03% | 0.01% | 0.01% | 77.95% |
Introducing these common raw materials does not mean that other materials are not suitable for concrete applications. The effects of various raw materials may vary depending on the region. Finding materials that are more suitable for local concrete applications is also the responsibility of technical personnel.
