Dosage of antifreeze in cold concrete method Nanling County antifreeze manufacturer Wuwei early strength antifreeze

Winter concrete is roughly divided into three categories: cold concrete, negative temperature concrete and early strength concrete.

Cold concrete means that except for the mixing water, which must remain liquid, other aggregates are not insulated, and no insulation measures are taken after pouring. It mainly relies on anti-freeze components. Ensure that a certain amount of supercooled liquid is slowly hydrated at negative temperature. This kind of concrete needs to be mixed with a large amount of inorganic salts to lower the freezing point. It should only be used when the construction conditions do not allow other measures to be taken.

Negative temperature concrete: When concrete is constructed at negative temperature, the sand, stone, and mixing water must be insulated and heat treated. During the concrete curing process, it must be combined with thermal insulation protection, Combined with comprehensive measures such as thermal storage method.

Low-temperature early-strength concrete: Construction at low temperatures around 0°C or not very low negative temperatures, using only heated mixing water and supplemented by comprehensive heat storage methods Keep the concrete hardening and strengthening at a positive temperature.

The function of adding antifreeze to cold concrete and negative temperature concrete is to lower the freezing point of the liquid phase in the mixed species so that the cement can continue to hydrate at negative temperature. Therefore, it is used Antifreeze type antifreeze, negative temperature concrete uses heating raw materials and heat storage and insulation maintenance to make the initial temperature of the concrete always higher than the lowest temperature outside, so the amount of admixture is less than that of cold concrete.

Low-temperature early-strength concrete only needs to add early-strength antifreeze.

Amount of antifreeze

If concrete is not mixed with antifreeze, its strength will be lost immediately after freezing. 40%~60%. If properly maintained, no frost damage will occur when frozen, and the state at this time is called critical frost resistance strength or critical maturity.

Hardened concrete will not cause frost damage if it is frozen at one time. Repeated freezing and thawing will damage the strength, cause cracks in the concrete, and the surface will peel off until it is destroyed.

The amount of antifreeze should be enough to ensure that the concrete has a liquid phase at the lowest construction temperature and hardens at negative temperatures.

Due to the slow growth of cold concrete strength, the 28d strength can generally only reach 50% to 60% of the standard curing strength, and can only be used for floors and building foundation pads. layer, secondary road surface, slope protection board, retaining wall and house foundation, etc. If a large amount of chlorine salt is added, it may cause corrosion of steel bars. Therefore, pouring is generally only allowed in unreinforced structures. The appearance of the structure has special requirements, the structure is under dynamic load, the structure is often exposed to heat above 60℃ during the use of the building, especially the hydraulic structure with water pressure, and the structure containing acid, alkali or sulfate Structures in contact with corrosive water and large concrete structures with a surface coefficient less than 2.5 should not be constructed with cold concrete.

When determining the amount of salt in cold concrete, it must be based on the temperature of the concrete that is hardening within 15 days, rather than the outside air temperature. Its dosage is also closely related to the surface coefficient of the structure, thermal resistance coefficient (moisturizing coverage conditions), warehouse temperature, cement hydration heat, cement dosage, air temperature, and the alkalinity (dissolved salt) of the concrete aqueous solution. When the temperature decreases, the amount of salt added will increase; if the insulation conditions are good, the amount of salt added should be reduced; if the heat of cement hydration is high and the temperature of the warehouse is high, the amount of salt added can also be reduced.

Therefore, it is very difficult to try to find the accurate dosage of a certain salt at a certain temperature through theoretical calculations. It can only be determined through experimental methods based on temperature.

Antifreezes used in concrete include: chloride salts, antifreezes compounded of chlorine salts and rust-inhibiting components, nitrite and nitrate antifreezes , alcohol-based organic compound antifreeze, antifreeze compounded with organic compounds and inorganic salts, and antifreeze compounded with antifreeze components and early strength, air entraining, and water reducing components. The performance of various types of antifreeze will be explained in the chapter on admixtures.

The amount of antifreeze can be determined according to the test method specified in "Concrete Antifreeze" (JC 475-92).

When the temperature is -10℃, -15℃, and -20℃, the specified temperatures of -5℃, -10℃, and -15℃ are used for testing respectively. . First, test specimens of benchmark concrete (standard cured concrete without antifreeze), tested standard cured concrete (standard cured concrete mixed with antifreeze), and tested negative temperature concrete (concrete mixed with antifreeze and cured at specified temperatures) are made. , respectively calculate the compressive strength R of the benchmark concrete after standard curing for 28 days, the tested concrete after standard curing for 28 days, curing under specified negative temperature for 7 days, and then curing under standard conditions for 28 days or 56 days. , RCA, RAT (MPa), and then calculate the intensity ratio between them.

A large amount of antifreeze is costly and ineffective

1. In order to ensure project quality and reduce project costs , Reduce the difficulty of construction, and winter construction can only be carried out as a last resort. Cold concrete construction should only be used as a last resort, because the exact amount of antifreeze in cold concrete is difficult to determine. In order to ensure that the concrete is not damaged by freezing, the amount added is often more than what should be added. Even if the amount is exceeded, if the temperature changes suddenly, you will still suffer from freezing damage.

Add large amounts of ��Antifreeze not only slows the early strength development, but also affects the durability of concrete to a certain extent no matter what measures are taken. Due to the low strength development speed, it is impossible to remove the formwork early and the construction progress cannot be accelerated, which is equivalent to increasing the cost in vain.

2. The scope of the project that should be carried out in winter can be reduced to a very small size. For example, underground projects (tunnels, underground factories, etc.), ground foundation projects, large-volume concrete and projects that easily store heat on the ground do not need to take winter construction measures at any temperature, as long as water reduction and slump reduction are adopted. This can ensure the quality of winter construction. If necessary, the heat storage method can fully meet the requirements.

For the slabs and columns on the first floor of ground factories, civil buildings and projects that are easy to insulate, when the temperature is below -10℃, measures should be taken to reduce water and reduce slump After the temperature is reached, the heat storage method is adopted. If necessary, heating the water and sand can ensure the quality and avoid freezing damage. When the temperature is -15~-10℃, in addition to the above measures, add a small amount of early strength agent appropriately.

In the concrete construction of the Hetao irrigation area in Inner Mongolia, the author prepares materials every winter and pours concrete in early spring. Although the temperature was as low as -15°C during the concrete pouring period, it was still in the warming season. Seizing this favorable opportunity, the above-mentioned heat storage construction methods were successfully adopted, which greatly saved project costs.

For structures that are higher than the ground and above the second floor, the temperature is above -10℃. Taking the above measures and adding early strength agent can also ensure the quality. When the temperature is as low as -10℃, construction should be avoided as much as possible.

In short, winter construction should be avoided as much as possible. In winter construction, the heat storage method should first be used, followed by material heating combined with heat storage method, and then a small amount of early strength should be added. agent. This not only reduces the cost, but also improves the quality and eliminates future worries. At the same time, it does not affect the construction progress.

Steam curing is suitable for factory-style precast concrete. The electric heating method consumes a lot of power and is not suitable for on-site use. The thermal storage method is not only simple and widely adaptable, but also fully meets the requirements of energy conservation and emission reduction in today's era.