How much do you know about concrete antifreeze during winter construction? Laian antifreeze price Dingyuan Zaoqiang antifreeze manufacturer

1. Winter construction of concrete

Regulations on the start and end time of winter construction

Winter construction measures should be adopted for the construction of concrete structure projects. The first day when the temperature is stably lower than 5℃ for 5 consecutive days can be taken as the starting date of winter construction. When the temperature rises, the last day when the temperature is stably higher than 5℃ for 5 consecutive days will be taken as the end date of winter construction. The date between the first day and the last day is the concrete winter construction period.

The effect of temperature on the performance of concrete

When the ambient temperature is low, the hydration reaction of cement is slow, which affects the concrete Growth in intensity. The test shows that for every 1°C decrease in temperature, the hydration of cement decreases by about 5% to 7%. In the range of 1°C to 0°C, the hydration activity of cement decreases drastically and the hydration is slow. Generally, when the temperature is below a certain range of 0℃, free water will begin to freeze. When the temperature reaches about -15℃, almost all free water will freeze into ice, causing the hydration and hardening of cement to completely stop.

When water is converted into solid ice, its volume increases by about 9%, causing internal stress in the concrete, causing relative displacement of aggregates and cement particles and internal Moisture migrates to the negative temperature surface and forms ice aggregates in the concrete body, causing local structural damage.

A certain amount of antifreeze added to the concrete mixing water will lower the freezing point of the aqueous solution. The degree of reduction in the freezing point depends on the type and dosage of the antifreeze or solution. related to the concentration. The effectiveness of antifreeze depends largely on the concentration of the solution and the negative temperatures to which the concrete is subjected during hardening.

The main purpose of adding antifreeze to concrete is to maintain a sufficient liquid phase at negative temperatures so that the hydration of cement can continue; turn to positive After heating, the strength of concrete can further increase and reach or exceed the design label.

Notes on concrete winter construction

(1) Requirements for materials and material heating

① For the cement used in preparing concrete during winter construction, Portland cement and ordinary Portland cement with high activity and high hydration heat should be given priority. Cement used for steam curing should be given priority. The variety should be determined through testing. The strength of cement should not be less than 42.5 grade and the water-cement ratio should not be greater than 0.6. Cement should not be heated directly. It should be transported to a greenhouse for storage 1 to 2 days before use. The temperature of the greenhouse should be above 5℃.

② Because the specific heat of water is about 5 times that of sand and stone aggregates, the method of heating water should be given priority when mixing concrete in winter, but the heating temperature must meet the specified values.

③ Aggregates are required to be cleaned and stored in advance to ensure that the aggregates are clean and free of frozen blocks, ice and snow. All winter aggregate storage sites should be located on higher ground without water accumulation.

④The temperature of sand and stone for concrete mixing during winter construction must meet the temperature required by thermal calculations. The heating method can be adapted to local conditions, but steam heating is the best method.

⑤No matter which method is used to heat the raw materials, when designing the heating equipment, the maximum daily material consumption and the required temperature must be found first. According to the raw materials From the initial temperature and specific heat, find the total heat required. Also consider the heat loss during the heating process. With the total heat required, the type, size and number of heat sources can be decided.

(2) Mixing

Concrete should not be mixed in the open air. A greenhouse should be set up as much as possible, and large concrete mixers should be used first. capacity of the mixer to reduce heat loss from the concrete. Before blending, rinse the blender with hot water or steam. The mixing time of concrete is 50% longer than the specified time at normal temperature. Since mixing cement with water at around 80°C will cause sudden solidification, the order of material feeding is to first add water and sand into the mix, and then add cement. If it can be ensured that the hot water does not come into direct contact with the cement, the water can be heated to 100°C.

(3) Transportation

The transportation time and distance of concrete should ensure that the concrete does not segregate or lose Plasticity. The main measures are to reduce transportation time and distance; use large-volume transportation tools and properly insulate them.

(4) Pouring and curing

Before pouring concrete, the formwork and steel bars should be removed from the Freezing snow and dirt, try to pour concrete as quickly as possible to prevent excessive heat loss. The exit temperature of the concrete mixture should not be lower than 10°C, and the mold entry temperature should not be lower than 5°C. When using heating curing, the temperature of concrete before curing shall not be lower than 2℃.

When heating and curing the integral structure, the location of the construction joints should be set at a place where the temperature stress is small. When the heating temperature exceeds 40°C, temperature stress will inevitably occur inside the structure due to the high temperature. Therefore, the opinions of the design unit should be sought before construction and construction joints should be set at appropriate locations within the span. Leave the construction joints open, and immediately use 3 to 5 atmospheric pressure airflow to blow off the cement film, sewage and loose stones on the joint surface after the cement is finally set.

2. Composition of antifreezep>

The key to the production of powdered antifreeze lies in the selection of formula and the uniformity of product quality. For liquid products, the compatibility between components in aqueous solution must be considered. No precipitation, crystallization, floc is allowed in liquid products, and the consistency must be suitable for pipeline transportation.
Selection of antifreeze for winter construction

Concrete for winter application 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.

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