Concrete mixing station technician A heard the discussion topic raised by technician B of the admixture plant today and sighed: "Wow, the topic of your conversation today is interesting!"
B said: "Every winter, don't the people at the mixing station and the people at the admixture factory argue about this matter?"
A said: "That's true. The admixtures have frozen. How can we prevent the concrete from freezing?"
B said: "Ha, this can't be said clearly in just one or two sentences. What do you mean when you say concrete doesn't freeze?"
A said: "This can't be said in one sentence. You can tell clearly. If there is water in the concrete, it means it is not frozen. Because there is water, the cement hydration reaction can continue, that is, the concrete is not frozen."
B said: "Yes, let the water in the concrete reach zero degrees without freezing, we have to..."
A said: "Wait, I Let me correct you, the water in concrete will not freeze when it reaches zero. Because part of the water seeps into the gaps between the cement particles, and the gaps are too narrow, the water will produce capillary action inside, and the freezing point will drop a lot."
B said: "You are right. I should change it to say that to prevent the water in the concrete from turning into ice, some chemicals must be added, such as salt, sodium nitrite, etc., to dissolve the water in the concrete. When the ion concentration of the mixing water increases, the freezing point drops."
A said: "Also, the concrete must drink some wine, and the concrete must drink some wine." It's fake wine."
B said: "Ha, you still remember the article about drinking from concrete. But to lower the freezing point of water, you need to add The amount of medicine that goes in is very large. For example, if sodium nitrite is added to 180 kilograms of water to 32 kilograms, the solution will start to freeze and the temperature will be -6 degrees Celsius. Calculated in this way, 1 ton of solution must contain at least 142 kilograms of sodium nitrite."
A said: "But according to my experience, this small amount of sodium nitrite is enough to prevent concrete at 10 degrees Celsius from freezing."
B said: "Yes, yes, this means that adding antifreeze to lower the freezing point of water is only one of the purposes. In fact, the more important thing is to prevent the water from completely freezing into ice, and to leave more The liquid water in the cement can continue the hydration reaction, which is the so-called partial ice formation theory."
A said: "Is there anything else?"
B said: "Also, the third purpose is that after adding certain substances to the water, the ice crystals are no longer monolithic, but relatively loose. The ice crystals of the sodium nitrite solution are needle-shaped, and they are a group inserted randomly into each other, like a duck rack that has been chopped twice, with flocculent ice filling in it, like duck meat that has not been picked clean. ”
A said: "Oh, you just can't forget to eat, and the concrete blocks turn into meat when they reach you." ”
B said: "This is the theory of ice crystal change." The antifreeze pumping agent used in winter uses these three solutions at the same time, so only a small amount of antifreeze can be used to prevent concrete from freezing. ”
A said: "It would be great to be able to prevent the concrete from freezing and the antifreeze from freezing at the same time." ”
B said: "This is easier in the antifreeze pumping agent where the traditional high-efficiency superplasticizer is the masterbatch. It can be used in the antifreeze pumping agent where the polycarboxylic acid is the masterbatch." It is not possible to meet both needs in the medicine. "
A said: "What is a traditional high-efficiency water reducing agent?"
B said: " It refers to a series of sulfonic acid-based high-efficiency water reducing agents invented starting from the first patent of naphthalene sulfonate formaldehyde condensate in 1960. When they are compounded into antifreeze, they use a large amount. Coupled with a large amount of inorganic salts that play an antifreeze role, such as sodium nitrite, the overall concentration of the solution is very high, the chemical activity of the water is low, and the strength of the concrete increases slowly. . ”
A said: "There is information that sodium nitrite can make water freeze at 19 degrees Celsius." ”
B said: "Hey, at such a low temperature, 1 ton of sodium nitrate solution will account for 380 kilograms." ”
A said: "Yes, the traditional high-efficiency antifreeze always feels very thick and sticky, but it does not freeze at zero degrees Celsius." ”
B said: "Ice ballast will also appear when the amount of antifreeze component is not enough." However, a solution with such a high viscosity will greatly change the ice crystal structure. Even if it freezes, it will not be solid and will melt easily. ”
A said: "It's like this in the additive tank, but it's still very frozen in the delivery pipe. Even if it's not all ice, the many crystals will freeze it." The pipe is blocked. ”
B said: "So in the north, people always install a mixer or a steam heating pipe in the material tank; and they have to install it back at one end of the delivery pipe." water valve to allow remaining liquid to flow back into the tank. It's quite troublesome anyway. ”
A asked: "What if it is a polycarboxylate water-reducing agent?"
B said : “The raw material of PC (polycarboxylic acid, the same below) agent is polyether, which itself has the effect of lowering the freezing point. Because the concentration is different, the freezing point is lowered differently. The freezing point of PC agent with a concentration of 10% was measured by an instrument to be -6 degrees Celsius. ��I am also a little confused. After a technician added 20 kilograms of sodium gluconate to the PC agent, it was freezing at -5 degrees Celsius. "
A asked: "What if I don't want to freeze?"
B said: "This The technician continues to try. As a result, I added 50 kilograms of sodium nitrite to the solution mentioned above and it was still frozen. Then I added some 'triethyl' to the solution. After 24 hours, a thin layer of ice was frozen on the surface. The ice gradually became colder after freezing for a longer period of time. thicker. ”
B continued: "If 100 kilograms of ethylene glycol are used, this solution will not freeze in an environment of -10 degrees Celsius." But if you want to prevent concrete from freezing, less than 50 kilograms is enough. I would like to make a special note that it is okay to see ice edges on the surface, as the antifreeze component is still in the solution. And because part of the water evaporates, the remaining solution has a higher concentration and is less likely to freeze. The cost of the latter is much lower. ”
A asked: "Will adding such a large amount of antifreeze affect the strength of the concrete?"
B said: "It will definitely have an impact. To put it in a nutshell, it will also greatly slow down the setting of concrete. You have to use a setting accelerator to adjust it. "
B asked: "Will the acceptance strength fail?"
A said: "PC It's okay to use the traditional high-efficiency agent as the masterbatch, but it's hard to tell if the traditional high-efficiency agent is used as the masterbatch, but the 7-day strength can hardly meet the requirements. Since the concrete mix ratio is designed with a large strength margin, the actual structure naturally maintains for a long time, and some losses are not obvious. "
B asked: "Which subject does this belong to?"
A said: "It belongs to silicon." Physics and chemistry of acid salts. You ask, why are you doing this, are you planning to study further?"
B said: "Go back online and order a book and take a look. ”
<img src="/upfile/202210/2022101830586343.jpg"/
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