Some friends in the admixture industry like to call sodium chloride salt. In fact, the raw materials that can be used as antifreeze are all inorganic salts. In daily life, salt is generally sodium chloride, but in industrial production, it is easy to cause ambiguity.
I will give a conclusion first, and then explain why this situation occurs. The sodium chloride dosage in the table below may cause some controversy, but in fact, the antifreeze formulas of most admixture manufacturers in the north have this ratio.
In the northern region, a large number of admixture companies use the ratio of sodium chloride: sodium nitrite = 1:1 when mixing antifreeze. The most significant advantage of this combination is cost savings. The price of sodium chloride is about 500-600 yuan/ton, and the price of sodium nitrite is 4,000 yuan/ton. The 1:1 combination can reduce the average price of antifreeze components to 2,250 yuan/ton. At minus 15 degrees Celsius, if the antifreeze component is used up to 15%, the cost can be controlled at 337.5 yuan/ton. Taking North China as an example, the low temperature will not reach minus 15 degrees most of the time. Since winter construction begins, if the antifreeze is gradually increased as the temperature decreases and the average amount of antifreeze is controlled, antifreeze can be guaranteed throughout the winter. The average cost of components is 150-200 yuan/ton.
The general meaning is that, under the premise that the additive content is 2.0% of the amount of glue, every time the temperature drops by one degree Celsius, the total amount of antifreeze will increase by 100%. one part. The temperatures given in the picture are the lowest temperatures of the day. The dosage in the 2.0% dosage column can ensure that the admixture itself does not freeze.
When the additive content is more than 2.0% of the glue content, you can also use the ratio corresponding to 2.0% in the above table. After all, less antifreeze is added. The concrete may be fine, but there is a chance that the admixture will freeze first.
This value is just my experience value. I once used this ratio for compounding, and there was no problem in using the mixing station. It feels like I haven't had any serious contact with antifreeze application in several years. I don’t know if the current ratio has been re-optimized. The above ratio is not an iron rule that must be followed. I once used only 6% sodium nitrite at minus 8°C. If you put the admixture bottle outside and put it outside, it will freeze the next day, but there is no problem when using concrete. Of course, in order to avoid the negative effects caused by freezing of admixtures, it is best to ensure that the admixtures do not freeze. The frozen part of the admixture is water. It would be good if the ice water can be mixed with the admixture and extracted together during concrete production. Once you encounter a situation where only the remaining part of the liquid can be extracted, the homogeneity of the admixture will be destroyed and cause unnecessary effects. After all, sodium chloride is cheap. . .
I personally remain vigilant about the use of sodium chloride, but I am not completely opposed to it. I specifically checked the relevant national standards.
The admixture standard 8076 does not strictly indicate what standard the chloride ion content in the admixture must be lower than. This indicator is so broad that it is specified by the manufacturer. What I understand is that the manufacturer says that the lower level is enough to be considered qualified. This feeling of being both a referee and playing a game is very satisfying.
And the antifreeze sodium nitrite itself has a rust-inhibiting effect. One rust-promoting and one rust-inhibiting functions offset each other and ultimately only play the role of anti-freeze and early strength. , pretty good too.
In addition, some standards for concrete do not stipulate the upper limit of the chloride ion content of the admixtures used. There is only one standard for the total chloride ion content of concrete.
In the concrete standard "Concrete Quality Control Standard GB50164-92", Section 3 stipulates that for reinforced concrete in a humid environment that does not contain chloride ions, chloride ions The content shall not exceed 0.3% of the weight of cement; the chloride ion content of reinforced concrete in a dry environment shall not exceed 1% of the weight of cement.
As for admixtures, it is impossible to fully understand the chloride ion content of other raw materials for customers of their mixing stations. Well, I'm going to be a bit shady here, assuming that no other raw materials of concrete contain chloride ions, and all the chloride ions in concrete are exclusively occupied by admixtures. Under this assumption, we look at how much sodium chloride should be added to the admixture to reach the upper limit in the specification.
The more suitable upper limit of sodium chloride should be the maximum dosage of sodium chloride in the admixture is 14.4%. This dosage does not take into account whether other materials contain chloride ions. In actual circumstances, other materials in concrete cannot contain chloride ions. This data is only for reference. The actual significance is just to tell everyone that the national standards do not strictly prohibit the addition of chloride when adding antifreeze to admixtures in winter.
In addition to sodium chloride and sodium nitrite, there are other commonly used antifreezes, such as calcium chloride, calcium nitrate, and sodium sulfate. However, sodium sulfate mainly plays an early-strength role and cannot have an anti-freezing effect when the temperature is too low. Sulfate radicals will also increase the instability of concrete. Calcium nitrate is a good choice, and the price is not expensive. I remember that the price consulted this year was 1,500 yuan/ton. In previous years, calcium nitrate cost more than 2,000 and sodium nitrite cost more than 3,000. It is cheaper to mix sodium chloride and sodium nitrite. Calcium nitrate is relatively cheap this year, but the cost of using calcium nitrate alone is��High.
I once had a small accident when using antifreeze. When calcium nitrate was used together with Evonik's ether air-entraining agent in Germany, flocculent precipitates appeared. It is not obvious when the temperature is low, and the floc is especially serious when the flowers bloom in spring. If you happen to want to use calcium nitrate and add an ether air-entraining agent, you need to pay attention to this detail. It does not affect the performance of the admixture, but it does affect the appearance.
When checking the design specifications for chloride ion content, the next one is the air content specification for concrete. I believe that many friends have a misunderstanding that the air content affects the strength of concrete, so air-entraining agents are definitely not a good thing. In fact, the air content is also stipulated in the national specifications. A reasonable air content will not only not affect the strength of concrete, but will also improve other properties of concrete. For example, national regulations for water conservancy projects and severe cold environments state that the minimum air content of concrete is 5.5%. In other words, it is also stipulated by the state to increase the amount of air-entraining agent during winter construction. In the future, when the mixing station asks why there are so many bubbles in the admixture, the admixture technician can confidently say that you are following the party and listening to the country.
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