In low temperature conditions, in addition to using heating equipment, the following are some methods that can speed up the setting of concrete:
1. **Adjust the mix ratio**: Choose an appropriate type of cement, such as early-strength silicate cement, which has a large hydration heat and releases the highest strength at an early stage. Try to reduce the water-cement ratio and slightly increase the amount of cement to increase the hydration heat and shorten the time to reach the age strength.
2. **Use air-entraining agent**: While keeping the concrete mix ratio unchanged, the bubbles generated after adding the air-entraining agent will increase the volume of the cement slurry accordingly, improve the fluidity of the mixture, improve its cohesion and water retention, buffer the water pressure generated by the freezing of water in the concrete, and improve the frost resistance of the concrete.
3. **Add early-strengthening admixture**: Shorten the setting time of concrete and improve the early strength. Commonly used early-strengthening admixtures include sodium sulfate (2% of the amount of cement) and composite early-strength water test agent (5% of the amount of cement).
4. **Select high-quality aggregate**: Select aggregates with high particle hardness and few gaps, so that their thermal expansion coefficient is similar to that of the surrounding mortar to improve the frost resistance of concrete.
5. **Heat storage method**: Mainly used for projects with relatively thick structures at temperatures around -10℃. By heating the raw materials (water, sand, stone), the concrete can still store considerable heat after mixing, transportation and pouring, so that the cement hydration releases heat faster and strengthens the insulation of the concrete.
6. **External heating method**: Mainly used for projects with temperatures above -10℃ and not thick components. By heating the air around the concrete components, the heat is transferred to the concrete, or the concrete is directly heated so that the concrete can harden normally under positive temperature conditions.
7. **Use antifreeze admixture**: In temperatures above -10℃, a chemical that can lower the freezing point of water is added to the concrete mixture, so that the concrete is still in a liquid state at negative temperatures, and the hydration reaction can continue, thereby continuing to increase the strength of the concrete. Commonly used antifreeze agents include single antifreeze agents such as calcium oxide and sodium chloride, and composite antifreeze agents of sodium nitrite and sodium chloride.
8. **Optimize concrete pouring control**: In winter construction, it is necessary to continuously optimize and control the pouring of concrete, and strictly control the quality of materials. Do a good job of review to improve the basic quality of concrete.
Through the above method, the setting speed of concrete under low temperature conditions can be accelerated without relying on external heating equipment, thereby improving construction efficiency.