What raw materials should be selected for formulating polycarboxylate superplasticizer water reducer?

1. Mother liquor

Among the various types of mother liquors, the most commonly used are water-reducing mother liquor and slump-retention mother liquor. We believe that although the functionality of slump-retention mother liquor is very different from that of water-reducing mother liquor, the synthesis method is the same and only the synthetic raw materials are different. Calling it slump-retention mother liquor is more standardized in the classification of compound raw materials.

Perhaps you will hear some opinions saying "my water-reducing mother liquor is comprehensive, has slump-retention effect, and has high water-reducing effect". Basically, these are the words of salesmen to promote their own products. Compared with water-reducing agents such as naphthalene, polycarboxylic acid water-reducing agent does have slump-retention and high water-reducing effects. It's just a difference caused by different comparison objects. The water-reducing rate of polycarboxylic acid mother liquor can be increased by adjusting the ratio of acrylic acid to macromonomer, but the slump-retention performance of the mother liquor will be sacrificed. Under the game between increasing the water-reducing rate to highlight the cost-effectiveness and improving the slump-retention performance to ensure the use effect, the performance of water-reducing mother liquors on the market is basically the same.

There are more types of slump-retention mother liquors.

1). Synthesized by replacing HPEG process with TPEG macromonomer;

2). Synthesized by replacing part of acrylic acid with hydroxyethyl acrylate and using HPEG monomer;

3). Synthesized by TPEG monomer + hydroxyethyl acrylate. These will be introduced one by one in future articles. The author prefers to use the slump-retaining mother liquor without water-reducing effect at the beginning. This can easily measure the ratio of water-reducing mother liquor and slump-retaining mother liquor during compounding. Using slump-retaining mother liquor is a cost-effective process. The higher the requirements of concrete for slump-retaining effect, the greater the amount of slump-retaining mother liquor. Under the premise of ensuring the slump-retaining performance of concrete, the amount of slump-retaining mother liquor should be reduced as much as possible.

2. Retarder

Sodium gluconate: cheap, 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 of reducing the workability of concrete.

White sugar: slightly expensive, significant retarding effect, can improve the workability of concrete. The disadvantage is that it increases the final setting time of concrete at low temperature.

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

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, etc.

3. Defoamer and 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 dosage of air entraining agent should not be too high. Excessive air content causes the air compressibility to increase and produce an unsaturated state, increasing the pump pressure loss during pumping. In the process of updating and iterating polycarboxylic acid water reducer, the types of air entraining agent and defoamer are even more complicated than the mother liquor. The author prefers to use ether defoamer and ether air entraining agent from Evonik of Germany. The price is slightly expensive, but the advantage is the low dosage. It is only a few ten-thousandths of polycarboxylic acid water reducer. 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 retaining agent

When the workability of concrete cannot be completely improved by the above raw materials, you can consider using water retaining agents such as cellulose ether, polyacrylamide, and Wenlun glue to improve the workability of concrete. In commercial concrete, water retaining agents are rarely used. Too much water retaining agent will affect the collapse protection effect of concrete. Influencing the collapse protection effect is to increase the compounding cost of water reducer in disguise. The amount of cellulose ether is less than 0.03%.

5. Antifreeze and early strength agent

Various inorganic salts have antifreeze effects. 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. In order to reduce the compounding cost of polycarboxylic acid water reducer, some admixture manufacturers use sodium nitrite and sodium chloride with rust-proof effect. Antifreeze also has early strength effect. In addition, triethanolamine can be used to improve the early strength of concrete. It's just that the cost is also touching.

Introducing these common raw materials does not mean that other raw materials are not suitable for concrete applications. The effects of various raw materials vary from region to region, and it is the responsibility of technicians to find raw materials that are more suitable for local concrete applications.