1.heat storage method
For concrete construction in winter, if the temperature is around -10°C, and if the structure is relatively thick, it is best to choose the thermal storage method for construction. However, during the construction process, we must focus on the following aspects:
The raw material is heated. In the construction process, the raw materials (water, sand, stone) should be properly heated, so that the concrete will have a considerable amount of heat after mixing, transportation and pouring, so as to accelerate the speed of cement hydration and heat release.
Strengthen insulation.
During the construction process, it is necessary to strengthen the heat preservation of the concrete to ensure that the newly poured concrete has sufficient anti-freezing ability before the temperature drops to 0 °C, avoid freezing of the corners and exposed surfaces, and prolong the curing period. In winter concrete construction, the regenerative method requires a relatively simple process, easy operation, and relatively low cost. It is an ideal winter concrete construction method.
2. External heating method
The external heating method is mainly suitable for projects where the temperature is above -10°C and the components are not large. The external heating method is to heat the air around the concrete member, transfer the heat to the concrete, or directly heat the concrete, so that the concrete can harden normally under normal temperature conditions. In the construction process, the external heating methods mainly include the following:
* Stove heating. If it is a relatively small construction site, you can choose a stove for heating. However, we should pay attention that although the heating operation of the furnace is relatively simple, it often cannot greatly increase the temperature, and it is relatively dry. At the same time, the carbon dioxide released will carbonize the surface of the newly poured concrete, which will affect the quality of the project to a certain extent.
*Steam heating.
This heating method is also relatively easy to control, and the heating temperature is relatively uniform, which can keep the temperature of each part basically balanced, and make the concrete harden under humid and hot conditions. However, this method also has shortcomings, the cost is relatively high, and special boiler equipment is required. And the heat loss is large.
*Electric heating.
In the construction process, steel bars can be used as electrodes, or electric heaters can be attached to the surface of the concrete, so that the electric energy can be converted into heat energy to increase the temperature of the concrete. Although this method is relatively simple to operate, it is easy to consume electric energy under the condition of power shortage, and the danger is relatively high during the construction operation. In addition to the above three heating aspects, the infrared heating method can also be used to heat the concrete with a high-temperature electric heater or a gas infrared generator.
*mixed with antifreeze method
The antifreeze admixture method is mainly used in concrete construction at temperatures above -10 °C. Freezing agent, so that the concrete is still in the liquid phase at negative temperature, hydration can continue, so that the strength of concrete continues to increase.
4. Adjust the mix ratio
The method of adjusting the mix ratio of concrete construction in winter is mainly for concrete construction at a temperature of about 0 °C. During the construction process, the main points to be done are as follows:
* To choose the appropriate variety of cement. The selection of appropriate cement varieties is an important means to improve the frost resistance of concrete. According to the author's construction experience, early-strength Portland cement should be used. Therefore, the heat of hydration of the cement is relatively large. And the release strength is the highest in the early stage. Generally, the 3-day compressive strength is about the same as the 7-day strength of ordinary silica cement, and the effect is more obvious.
* Reasonably reduce the water-cement ratio.
According to the actual situation of the construction project, the water-cement ratio should be reasonably reduced, and the amount of cement should be reasonably increased, thereby increasing the heat of hydration and shortening the time to reach age strength.
*Add air-entraining agent.
In order to improve the fluidity of the mixture, improve its cohesion and water retention, buffer the water pressure caused by the freezing of water in the concrete, and improve the frost resistance of the concrete, we can add The air bubbles generated after the air-entraining agent increase the volume of the cement slurry accordingly.
