Admixtures play a vital role in improving the workability of concrete. It solves the problems faced by the emergence of new construction structures and techniques. There are many types of admixtures, and water-retaining agents are an admixture that can improve the performance and workability of concrete. However, there are certain standards for the use of each admixture. If it exceeds or fails to meet this standard, the expected effect may not be achieved, or costs may be wasted. Therefore, caution must be exercised when using admixtures. The following focuses on some water-retaining agents:
The advantage of cellulose ether is that the dosage is not high and the overall cost is not high, but the actual effect is obvious. Usually the blending amount is less than 0.05%. According to the chemical structure of the substituent, it can be divided into cationic, positive ionic and non-ionic ethers. According to the viscosity of cellulose, it can be divided into 50,000, 100,000, 200,000, 10 million, etc. According to the solubility, it is divided into instant water, soluble water and difficult to dissolve water. But each differs in nature. Cellulose has the effect of improving the water solubility and workability of concrete with twice the result with half the effort. The production and application of solid packaging is also very convenient. However, if excessive cellulose is added, the slump retention effect of concrete will be significantly reduced. It also has a negative impact on the compressive strength and compressive strength of concrete. Based on the advantages and disadvantages of comprehensive methylcellulose, using cellulose to retain water can be the first choice, but the dosage should be strictly controlled.
Polyacrylamide can be divided into cationic and anionic types, but the cationic type is slightly more expensive. The molecular content is 7 million, 10 million, 20 million, etc. In fact, if it is just to improve the workability of concrete, then using polyacrylamide is not very cost-effective. The outstanding advantage of polyacrylamide is its flocculation effect, which ensures that concrete does not disperse even in water. In addition, the negative effects of polyacrylamide are higher than those of methylcellulose, such as increasing the setting time of concrete, reducing the compressive strength and tensile strength, and problems will occur if it is left standing for a long time. The advantage is that in addition to being used in water, the effect is similar to that of cellulose at the same intake, and the cost can be saved by about half.
The above are two common water-retaining agents, as well as warm rubber and xanthan gum. These products are very expensive, and it is very difficult to produce and dissolve them in paste form. They must first be diluted according to a certain ratio, then stirred evenly, and finally used for compounding. The diluent can be mixed evenly and then added to the mixture. The properties of concrete can be adjusted to a certain extent. However, the production procedures are cumbersome, so they are not commonly used.
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