Winter antifreeze and early strength agent for concrete—calcium chloride

Calcium chloride antifreeze is commonly used as an antifreeze during road or house construction (construction industry) to protect roads or buildings. After calcium chloride is dissolved in water, it will fill the gaps between water molecules, so that at subzero temperatures, the arrangement of water molecules cannot freeze as usual, and it can play an antifreeze role. During road maintenance or construction, the use of calcium chloride antifreeze can achieve normal construction in low-temperature environments and protect the walls, roofs and foundations of roads and buildings from damage due to low temperatures.

Detailed application of calcium chloride early strength agent in anti-freezing, accelerating and rapid setting in building concrete, grouting cement materials, grouting material admixtures, etc.

Calcium chloride dihydrate flakes

Concrete early strength agent is one of the concrete admixtures. It refers to admixtures that can improve the early strength of concrete and have no significant impact on the later strength. The main function of the early strength agent is to accelerate the hydration rate of cement and promote the development of early strength of concrete; it has both drought strength and water reduction enhancement functions.

The main types of early strength agents include: chloride salt early strength agents, sulfate early strength agents, etc. Chloride salt early strength agents mainly include calcium chloride, sodium chloride, potassium chloride, etc. All chloride salt early strength agents have good early strength effects.

The strength of concrete is different when different early-strength agents are mixed. The early-strength agents that have better effects when mixed alone include calcium chloride, sodium chloride and sodium sulfate. The early strength effect of calcium chloride varies with the hardening temperature of concrete. Generally speaking, when the temperature is lower, the rapid hardening effect of calcium chloride is better, so calcium chloride is particularly suitable for winter construction of concrete.

Powdered calcium chloride

The mechanism of action of calcium chloride early strengthening agent:

The incorporation of chloride salt can increase the solubility of cement minerals and accelerate the hydration rate of cement minerals. For example, calcium chloride early strength agent: Calcium chloride CaCl2 can react with C3A to form hydrated calcium chloroaluminate that is almost insoluble in water and CaCl2 solution. CaCl2 can react with the hydration product Ca(0H)2 to form a hydrated calcium chloroaluminate that is almost insoluble in water and CaCl2 solution. Calcium oxychloride (CaCl23 Ca(0H)212HzO and CaCl2.Ca(0H)2.H20) reduces the concentration of Ca(0H)2 in the cement slurry, which is beneficial to the hydration reaction of C3S. The early precipitation of calcium chloroaluminate hydrate and calcium oxychloride solid phase accelerates the formation of cement slurry structure, which is beneficial to the development of early strength.

Reasonable addition of chlorine salt early strength additives will be beneficial to the early strength development of concrete. However, chloride-based early-strength additives can only be added to plain concrete without stiffeners. For reinforced concrete, especially prestressed reinforced concrete, and concrete with embedded metal parts, such additives should be used with caution. agent, limit the introduction of Cl- (chloride ion) content, and even prohibit its use. Although chloride salt early-strength agents cannot be used in reinforced concrete projects, calcium chloride early-strength agents are used in highway concrete projects and underground construction grouting technology projects. , The grouting method is widely used in fields such as dealing with karst roadbed collapse projects.

anhydrous calcium chloride

Advantages of calcium chloride early strengthening agent:

Calcium chloride has good early strength effect, low cost and wide application. Calcium chloride is a white powder or spherical granular solid. The appropriate dosage of calcium chloride is 0.5% to 1% of the cement mass. O%, can improve the strength of concrete, and at the same time reduce the freezing point of water in concrete to prevent early freezing of concrete.

Calcium chloride is a setting accelerator and early strength agent, which can speed up the hydration of cement and improve its frost resistance. Calcium chloride is added to the cement slurry, and the CaSiO3.h2o generated by the reaction is a flocculent colloid that is difficult to dissolve. When the amount of calcium chloride increases, the reaction proceeds in the forward reaction direction, and the amount of CaSiO3.h2o increases, thus achieving rapid setting. To achieve the best quick-setting effect, add calcium chloride solution (concentration 2%-5%) at 2%-3% of the cement volume.

Precautions for application of calcium chloride early strength agent:

1.Calcium chloride is used as the early strength agent. The disadvantage is that it contains Cl- ions, which will corrode the steel bars and cause cracking of the concrete. In order to inhibit the corrosion effect of calcium chloride on steel bars, calcium chloride is often combined with the rust inhibitor sodium nitrite (NaNO2).

2.Antifreeze containing chlorine and potassium ions cannot be used in concrete, so active aggregates or materials with oil mixed in aggregates cannot be used. Cement should be made of tricalcium aluminate, with a content of no more than 10% and a content of tricalcium silicate. No more than 45% ordinary Portland cement, and the cement cannot be less than No. 425.

3.When using steam to cure concrete, it is not easy to use chloride antifreeze, that is, antifreeze containing calcium chloride, magnesium chloride, and sodium chloride cannot be used.