Ensuring the workability of concrete should be regarded as one of the few mountains that weigh on the heads of admixture workers. Dry admixtures range from naphthalene series to polycarboxylic acid. It is expected that the daughter-in-law of many years will live a good life for a few years. Who would have thought that the campaign to reduce adhesive materials in the concrete industry is going on with great vigor. Polycarboxylate water-reducing agents are very good compared to naphthalene series, but they are relatively sensitive to cement and sand materials. In terms of use, this is the original sin of polycarboxylate water-reducing agents. It is estimated that they will not be able to be cleaned in this life. (There was a change in the admixture during the operation of the mixing station today. In fact, the moisture content of the sand fluctuated too much and was not properly controlled. It took an explanation and a live demonstration to solve the problem.) But for Mao Zedong’s sake, polycarboxylic acid Water reducing agent still needs to be used. As for the workability, I'll leave it to other ingredients to improve. Below I will mainly introduce some common water-retaining agents and some methods to increase workability. Each material has an upper limit for improving the workability of concrete. Beyond this limit, there are either side effects or high costs. It needs to be used flexibly in daily work.
Cellulose has an immediate effect on improving the water retention and workability of concrete. It is also very useful in solid packaging production. Convenient, but as the amount of cellulose gradually increases, it will significantly affect the slump retention effect of concrete. It also has a negative impact on the 28-day compression and flexural resistance of concrete, and the impermeability of concrete will be improved. Based on the advantages and disadvantages of cellulose, if there is a need to increase water retention requirements, cellulose is considered a priority, but attention should be paid to the amount during application.
Polyacrylamide: Polyacrylamide can be divided into cationic and anionic types. The cationic type is slightly more expensive. According to molecular weight, it can be divided into 7 million, 10 million, 20 million, etc. I don't have much exposure to polyacrylamide. I have used it before when dealing with mud from piling drills at construction sites. I have only heard friends use it in concrete. I feel that if it is just to improve the workability of concrete, polyacrylamide is not cost-effective. The outstanding advantage of polyacrylamide is its flocculation effect, which ensures that the concrete does not disperse even under water. In addition, the side effects of polyacrylamide are also higher than those of cellulose, such as prolonging the setting time of concrete, reducing the flexural and compressive strength, and delamination after long standing time. The advantage is that in addition to underwater applications, compared with cellulose, the effect is about the same at the same dosage, and the cost is about half cheaper.
In addition to the above two common water-retaining thickeners, there are also warm rubber and xanthan gum. The powder of this type of product is too expensive, and the production and dissolution of the paste is a headache. First, it needs to be diluted in a certain proportion (such as 20 times) and stirred evenly before it can be added to the compound. Although it is also helpful to improve the workability of concrete, it is too troublesome to produce and is rarely used.
There is another large category, which are water-retaining agents without specific product names that are synthesized or compounded by each manufacturer. I won’t go into too much detail on this. Practice brings true knowledge. If any friends encounter whether it works well or not, they can only look at the experimental data.
Another type of retarder that can increase the workability of concrete is maltodextrin and sugar. Sodium gluconate is an excellent retarder. Its advantage is that it can not only improve the retarding effect, but also provide a certain water-reducing effect. It is helpful to reduce the amount of water reducing agent. The disadvantage is that as the amount of sodium gluconate increases, the workability of concrete will decrease. If you don’t want to add additional water-retaining agents, you can try replacing part of the sodium gluconate with maltodextrin or white sugar. The disadvantage of maltodextrin is that adding too much will affect concrete loss. According to the literature, maltodextrin is made from corn and uses specific enzymes to hydrolyze only starch, leaving behind cellulose and protein. So maltodextrin is kind of a mixture of sodium gluconate and cellulose. Compared with sodium gluconate, white sugar also helps to improve the workability of concrete and can make the slurry more viscous. The disadvantages are that it is more expensive than sodium gluconate and has a greater impact on the setting time. It cannot be used in winter, otherwise it will greatly extend the setting time of concrete.
Air-entraining agents can also effectively improve the workability of concrete. The principle is to create tiny bubbles to fill in the concrete slurry, blocking the capillary channels to prevent free water from escaping out of the slurry, thereby improving the workability. Nowadays, commercial concrete containing air-entraining agent components is almost standard. As long as the air content of the concrete is not exceeded and controlled within 5%, the slump-preserving performance, workability, and pumpability of the concrete can be improved. If there are many large bubbles on the surface of the concrete, you can choose to use it with a defoaming agent. Large apparent bubbles are more likely to burst than microscopic small bubbles. A reasonable air-entraining agent and defoaming agent ratio can eliminate only large bubbles and leave microscopic small bubbles that are beneficial to concrete.
The application of slump-preserving mother liquor can also improve the workability of concrete to a certain extent. However, each region has different needs for tantalizing mother liquor and it is difficult to generalize.
Finally, I thought of a material that does all the harm but one benefit, and the most significant improvement in the workability of concrete is. That is the mud contained in the sand. If the mud content of the sand reaches more than 4%, the concrete can basically be guaranteed to be in good condition. This is probably the only contribution of mud to concrete.Stone powder can also increase the workability of concrete, but this cannot be compounded with admixtures. With the rise of machine-made sand, stone powder should be able to enter the vision of more mixing stations in the future.
This article mainly introduces various raw materials that can improve the workability of concrete. The addition ratio, effect, price cost, and side effects are different. My personal The order of priority is 1. Air-entraining agent 2. Maltodextrin, sugar, and cellulose. The three can be used in conjunction with each other at the same time. If the problem still cannot be solved, the concrete mix ratio must be adjusted.
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