The dosage and application scope of early strength agent, antifreeze and waterproofing agent. Price of early strength antifreeze in Bengbu

Early strength agent refers to an admixture that can promote setting and improve the early strength of concrete without significant impact on the later strength. Those that only play a role in promoting coagulation are called coagulants. At present, commonly used early strength agents include chloride salts, sulfates, and triethanolamine.

1. Chloride salt

Chloride salt early strength agent mainly includes calcium chloride (CaCl2) and sodium chloride (NaCl), of which calcium chloride is the earliest and most widely used early strengthening agent. The early effect of chlorine salt is mainly through the formation of calcium chloroaluminate hydrate and calcium oxychloride to achieve early strength. In addition to promoting coagulation and early strengthening effects, calcium chloride also has the effect of lowering the freezing point. Because it contains chloride ions, it will accelerate the corrosion of steel bars, so the dosage must be strictly controlled. The dosage is generally 1% to 2%, which can increase the ld strength by 70% to 140% and the 3d strength by 40% to 70%. It has little impact on the later strength and can improve the frost resistance, but it increases dry shrinkage and reduces Freeze resistance.
The dosage, function and application of sodium chloride are basically similar to calcium chloride, but the effect is slightly worse , and the intensity will decrease to a certain extent in the later stage.
“Technical Specifications for the Application of Concrete Admixtures” (GB50119) and “Construction Quality Acceptance Specifications for Concrete Structural Engineering” (GB50204 ) stipulates that in reinforced concrete, the dosage of calcium chloride shall not exceed 1%, and in unreinforced concrete, the dosage shall not exceed 3%; concrete that is often in humid or water level changing areas, concrete that is subject to the action of corrosive media, and aggregates Chloride salt early-strength agents are not allowed to be incorporated into alkali-active concrete, thin-wall structural concrete, mass concrete, prestressed concrete, decorative concrete, and concrete structures using cold-drawn or cold-drawn low-carbon steel wires. To prevent chlorination Calcium has a corrosion effect on steel bars and is often used in combination with rust inhibitors.
Chloride salt early strength agent is mainly suitable Construction of concrete and early-strength concrete in winter is not suitable for steam curing concrete.

2. Sodium sulfate

Sodium sulfate (Na2SO4), usually anhydrous sodium sulfate, also known as Yuanming powder, is one of the sulfate-based early strengthening agents and is a commonly used early strengthening agent. The early strengthening effect of sodium sulfate is through It is achieved by generating dihydrate gypsum and then hydrated calcium sulfoaluminate. Sodium sulfate has retarding and early strength effects. The dosage is generally 0.5% to 2.0%, which can increase the 3d strength by 20% to 40%. After 28 days, the There is basically no difference in strength and no corrosion effect on steel bars. When the aggregate is alkali-active aggregate, sodium sulfate cannot be added to prevent alkali-aggregate reaction. Excessive dosage will cause sulfate corrosion. A large amount of sodium sulfate will significantly increase the viscosity of the concrete mixture, which is detrimental to construction (especially the surface is difficult to smooth and smooth). The application range of sodium sulfate is wider than that of chloride salt early strength agent.

3. Triethanolamine

Triethanolamine is a colorless or light yellow oily liquid, non-toxic. It is alkaline and is a non-ionic surfactant. The early strengthening mechanism of triethanolamine is different from the first two early strengthening agents. It does not participate in the hydration reaction and does not change the hydration products of cement. It can reduce the surface tension of the aqueous solution, make the cement particles easier to wet, and increase the dispersion of the cement, thus speeding up the hydration rate of the cement and playing a catalytic role in the hydration of the cement. The increase in hydration products increases the early strength of cement. The dosage of triethanolamine is generally 0.02% ~ 0.05%, which can increase the 3D strength by 20% ~ 40%, has little impact on the later strength, improves frost resistance, anti-permeability and other properties, and has no rust effect on steel bars, but will increase the Great shrinkage.

4. Other early strength agents

In addition to the above three early strength agents, there are also other early strength agents in the project Use gypsum, sodium thiosulfate (sodium soda), alunite (potassium aluminum sulfate), calcium nitrate, potassium nitrate, sodium nitrite, calcium nitrite, sodium formate, sodium acetate, sodium dichromate, etc. Early strengthening agents are more effective when used in combination. High-efficiency water-reducing admixtures can improve the early strength of concrete to varying degrees. If the early strength agent and water reducing agent are used in combination, the early strength can be further improved, the later strength can be increased, and the construction properties of concrete can be improved. Therefore, the combined use of early strength agent and water reducing agent, especially the composite early strength water reducing agent of chlorine-free salt early strength agent and water reducing agent, has developed rapidly. Compound early-strength water-reducing agents such as sodium sulfate, calcium lignin, calcium sugar and high-efficiency water-reducing agents have been widely used.
Too much early-strength agent or early-strength water-reducing agent will cause concrete damage Frosting on the surface will reduce the strength and durability in the later period, and also have a negative effect on the protection of steel bars. Sometimes it will also cause premature setting or false setting of concrete.

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