Regarding the compound raw materials of polycarboxylate water-reducing agent
In recent years, polycarboxylic acid mother liquor synthesis technology has become increasingly mature through several iterations. It has evolved from the high-temperature esterification process of pure water to the normal temperature tap water method. Greatly lowers the synthesis threshold of polycarboxylate water-reducing agent. Thanks to this, most mother liquors on the market have similar properties, providing a relatively common communication basis for compounding technology. The raw materials of current compound polycarboxylate water-reducing agents can be roughly divided into the following categories: polycarboxylic acid mother liquor, retarder, defoaming agent, air-entraining agent, water-retaining agent, antifreeze agent, early strength agent, etc. Here we focus on introducing several commonly used types of compound raw materials that are convenient for adaptation operations.
The most commonly used mother liquors are water-reducing mother liquor and slump-preserving mother liquor. Some people in the market are accustomed to calling the slump-preserving mother liquor a slump-preserving agent. The synthesis method of the slump-preserving mother liquor includes: (1) Synthetic process of replacing HPEG with TPEG macromonomer; (2) Replacing part of the acrylic acid with hydroxyethyl acrylate and synthesizing with HPEG monomer; (3) Synthesizing with TPEG monomer + hydroxyethyl acrylate.
The initial slump-preserving mother liquor without water-reducing effect can easily measure the ratio of water-reducing mother liquor and slump-preserving mother liquor during the compounding process. The higher the concrete's requirements for slump-preserving effect, the greater the dosage of slump-preserving mother liquor. On the premise of ensuring the slump-preserving performance of concrete, the amount of slump-preserving mother liquor should be reduced as much as possible.
2. Retarder
The characteristics of various retarder are as follows: (1) Sodium gluconate: It is cheap and can provide a certain water reduction rate. The most cost-effective and the most common retarder in compounding. The disadvantage is that there is a certain probability of reducing the workability of concrete. (2) White sugar: It is slightly expensive, has a significant retarding effect, and can improve the workability of concrete. The disadvantage is that the final setting time of concrete is increased at low temperatures. (3) Maltodextrin: The price is about the same as sodium gluconate, and it can improve the water retention of concrete. The disadvantage is that it may increase the slump loss of concrete.
In commercial concrete compounding, the combination of the above three retardants is the most commonly used method. In addition, there are sodium citrate, sodium tripolyphosphate and so on.
3. Defoaming agent 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 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 updating and iterating polycarboxylate water-reducing agents, the types of air-entraining agents and defoaming agents are even more complicated than the mother liquor. Among them, ether defoaming agents and ether air-entraining agents are slightly more expensive, but their dosage is low. The dosage in polycarboxylate water-reducing agents is only a few ten thousandths.
4. Water retaining agent
When the workability of concrete cannot be completely improved by the above raw materials, you can consider using cellulose ether, polyacrylamide, warm wheel glue and other water-retaining agents to improve the workability of concrete. In commercial concrete, water retaining agents are rarely used. Too much water-retaining agent will affect the slump-preserving effect of concrete. The impact on the slump-preserving effect is a disguised increase in the compounding cost of the water-reducing agent. For example, the dosage of cellulose ether is less than three ten thousandths.
5. Antifreeze and early strength agent
Various inorganic salts have antifreeze effects. Commonly used antifreezes are sodium nitrite, sodium nitrate, calcium nitrate, etc. Sodium chloride is the cheapest, but chloride ions have the side effect of corroding steel bars. In order to reduce the cost of compounding polycarboxylate water-reducing agents, some admixture manufacturers use sodium nitrite and sodium chloride, which have rust-inhibiting effects. Antifreeze also has an early strengthening effect. In addition, triethanolamine can be used to improve the early strength of concrete.
