Polycarboxylic acid + antifreeze + pumping agent = polycarboxylic acid antifreeze pumping agent Bengbu early strength antifreeze water reducing agent

Polycarboxylic acid cannot be used as antifreeze

The winter construction method of concrete mixed with antifreeze was developed in the 1950s was founded in the 1990s. In the 1980s, antifreeze began to be compounded with water-reducing agents, and early-strength components and air-entraining components were also added, which promoted great progress in concrete winter construction technology and also brought considerable economic benefits. Modern antifreeze must be mixed with high-efficiency water-reducing admixtures, because reducing water consumption is equivalent to reducing freezing hazards.

Polycarboxylate high-performance water-reducing agent has the best comprehensive performance and the highest water-reducing rate among contemporary high-efficiency water-reducing agents. It is the most effective in reinforcing concrete, especially in improving early strength. Significantly. Therefore, polycarboxylate antifreeze attracted the attention of commercial concrete manufacturers as soon as it came out and was quickly promoted and applied.

However, the molecular structure and performance of polycarboxylate water-reducing agent are significantly different from traditional high-efficiency water-reducing agents. When using it as a water-reducing component in antifreeze, Antifreeze components commonly used in the past are often difficult to use or even unusable. In short, the antifreeze formula using polycarboxylic acid as the water-reducing component should be redesigned.

Basic starting point for antifreeze design
The design of concrete antifreeze must be considered from two aspects. First of all, based on the curing process selected after the concrete is formed, the antifreeze required when using the comprehensive thermal storage method for curing is different from that when using the negative temperature curing process in terms of formula and dosage. Second, antifreeze components to prevent concrete freezing damage are based on three types of principles. When formulating antifreeze, two or three types of different functional components are often used together, and these three principles are different:

One ​​is to lower the freezing point of water; the second is to directly react chemically with cement to accelerate the hardening of concrete, and also has a certain degree of freezing point lowering effect; the third is to distort the ice crystals after being added The frost heave stress is small and will not crack the concrete structure.

The design principles of antifreeze formula should be:

1. Mixed use

The meaning of compound refers to: This means that the harsh and complex winter construction environment of concrete should be taken into consideration, so it must be composed of high-efficiency water-reducing components, anti-freeze components, and air entrainment The components are composed of accelerating early strength components and homogenizer components. If the antifreeze is used in ready-mixed concrete, that is, commercial concrete, there must also be a small amount of retarding components; it also means that the antifreeze components should also play different roles. It is composed of antifreeze ingredients.

2. The minimum dosage of each component should be considered as much as possible

This can make The total dosage is reduced to a minimum. The dissolution of various chemical components into the concrete mixing water with a small total amount will reduce the activity of the water and prevent the cement particles from being fully hydrated. This is because the mixing water becomes a solution of several chemical substances and then the ions of these substances hydrate to cause water molecules. When combined into clusters, the molecular clusters lack electrical attraction and therefore their activity is reduced. The result of insufficient hydration of cement is a reduction in concrete strength. The activity of potassium carbonate, sodium nitrite and calcium chloride aqueous solutions at different temperatures is reduced. See the attached figure. However, it is not advisable to minimize the amount of superplasticizer just for the sake of cost reduction, because the high dispersion of superplasticizer promotes cement hydration, and the comprehensive effect of sufficient superplasticizer reduces the loss of concrete strength to Minimal, or showing no reduction.

3. Pay equal attention to safety and durability

Concrete mixed with antifreeze should not only be used to resist compression Strength is an indicator to evaluate its quality, but more attention should be paid to structural durability. Such as concrete density indicators such as impermeability, freeze-thaw resistance (i.e. frost resistance), holding strength of steel bars, carbonation resistance and chloride ion permeability. When switching to polycarboxylate high-performance water-reducing agent, the durability improvement is much more obvious than that of traditional high-performance water-reducing agent. Some substances used in admixtures are toxic, and mild toxicity can be prevented during operation. Substances that are highly toxic or easily emit harmful gases are prohibited from use. Safety during production and use is an issue that must also be considered.

4. Consider the characteristics of polycarboxylic acid

Choose one that is compatible with the chemical structure of polycarboxylic acid Antifreeze components and other components should not cause component degradation or react to form substances unrelated to antifreeze and water reduction performance.

Design approach
1. Polycarboxylate superplasticizer mother liquor

As an antifreeze pump The high-performance water-reducing agent and polycarboxylic acid mother liquor that deliver the backbone ingredients are generally compounded with 2 to 3 types. Some use early-strength type and slump-preserving type compound, and some use slightly higher cost self-antifreezing type and general-purpose compound. match. When the concrete is cured using the comprehensive thermal storage method - a process used by most construction sites in the 13 northern provinces and cities in my country that have winter application regulations, the amount of mother liquor can be slightly lower. For ordinary concrete, it is generally more than 0.1% based on the active ingredient per kilobase, C45 For grade concrete and above, it should be no less than 0.18%; when using negative temperature curing process, it should be no less than 0.2%.

2. Antifreeze components

Suitable for use with traditional high-efficiency water reducing agents naphthalene series and aldehydes Some of the eight types of compound antifreeze components such as ketone condensates and sulfonated melamine resins are not suitable for polycarboxylic acid systems. Antifreeze components suitable for one type of polycarboxylic acid may not be suitable for polycarboxylic acid synthesized by another process. Acids interact to cause toxicity. The author of this article believes that among inorganic substances so far, nitrates, chloride salts, and some carbonates can be used safely; among organic substances, low-carbon polyols, small molecular weight carboxylates, and certain phthalamine substances are also suitable for use. Considering that the liquid concentration of polycarboxylate antifreeze is significantly smaller than that of traditional high-efficiency antifreeze, when transported over long distances and stored without insulation facilities, the antifreeze liquid itself may freeze - mostly occurring when the temperature is below -5 for a long time. ℃ environment. Therefore, when preparing polycarboxylic antifreeze, organic and inorganic components are often compounded to increase the concentration of the solution.

It must be emphasized that even if the antifreeze freezes into ice, it will not affect the use effect after it melts. Keeping antifreeze from freezing and keeping concrete from freezing are two different concepts. If a single organic substance is used to keep antifreeze from freezing, the amount added is enough to reduce the strength of concrete.

3. Early-strengthening components that promote coagulation

The 6 most commonly used early-strengthening agents ——Chlorides, fluorides, sulfur-containing compounds (alkali metal and alkaline earth metal sulfates, thiosulfates, sulfate double salts, thiocyanates, etc.), nitrates and nitrites, organic amines, simple hydroxycarboxylates Among the acid salts, some are not suitable or compatible with polycarboxylic acids, so the selection range is narrow, and a suitability test must be conducted before determination. Sodium aluminate, potassium carbonate, sodium carbonate, aluminum sulfate, etc. are components of accelerators, but a small amount can be used as a coagulant. There is an urgent need to develop early strength components that are more suitable for polycarboxylic acid systems.

The slump-preserving polycarboxylate water-reducing agent is slightly retarded, and an additional retarding component is required when used. This becomes a disadvantage in low-temperature environments, so it is It is necessary to add a small amount of coagulant components to polycarboxylate antifreeze. In recent years, a few authoritative materials have disclosed the efficacy of sodium thiocyanate as an early-strengthening accelerator. Relevant U.S. patents in the last century also pointed out that this ingredient, as a trace impurity contained in sea waves, has a better early-coagulation and early-strengthening effect than triethanolamine. Its disadvantage is the tendency to promote rust caused by adding large doses. Norwegian experts have also pointed out the early and strong catalytic effect of calcium nitrate and calcium nitrate. The role of the latter in polycarboxylate superplasticizers has yet to be confirmed, but the role of the former has been confirmed by the practice of Wang Ziming, Tian Pei and others.

Picture: For antifreeze used in negative temperature curing process concrete, the setting accelerating component should be more powerful, that is, the dosage will not be increased but the effect will be better. , and at the same time, try to choose ones that have a superimposed effect on the early-strength components.

The air-entraining component is one of the necessary antifreeze components. In view of the fact that many previous discussions have been made, this article only follows the general trend.

Design misunderstanding
In the section discussing antifreeze components in this article, the "classic" nitrite antifreeze component is not included in the recommended application category. This is because nitrite should not be used in polycarboxylic acids, especially polycarboxylic acids synthesized using a redox system. If mixed, nitrites will easily decompose under acidic conditions and release yellow-brown nitrogen dioxide gas. , not only the anti-freeze function is lost, but also causing human injury and atmospheric pollution.

Nitrite is an oxidant, and it is unsafe to use it in combination with flammable methanol to produce antifreeze.

Calcium chloride is a good accelerator and early strength agent. It can react with the cement mineral tricalcium aluminate in concrete to form calcium chloroaluminate hydrate. It can also Reacts with calcium hydroxide to reduce the alkalinity of water in concrete, thereby accelerating the hydration rate of tricalcium silicate and causing early strength. However, calcium chloride solution forms a phase-separated system in polycarboxylic acid. It must be stirred well before use and is classified as "unusable". In addition, the influence of chloride ion content must be considered during use.

Hypo is a chemically unstable substance that easily interacts with the residual thiacetic acid in the raw materials for polycarboxylic acid synthesis, causing the solution to become turbid and thereby generating hydrogen sulfide. The solution will stink and the early strength properties will be lost.

It is more common that some early strength agents need to be increased in dosage in the polycarboxylic acid mother liquor to play the same role as in the traditional high-efficiency mother liquor. Once this situation occurs, the author of this article recommends finding a "partner" to use together.

The collocation taboos mentioned above are all based on experience and even accident examples, but it is still inevitable that there will be mistakes.

In short, as far as the compounding process of antifreeze pumping agent is concerned, the ease of use of one polycarboxylic acid mother liquor does not mean that the other one will be equally adaptable. Antifreeze The same goes for other ingredients, which must be fully tested first. It is really taboo to apply the experience of traditional high-efficiency superplasticizer mother liquor to polycarboxylic acid series "as a matter of course".