Concreting technology in winter conditions 1. General information about concreting in winter conditions

In our country, buildings and structures made of monolithic concrete are built year-round. It is known that at a temperature of + 50 Concrete mixes slowly harden. The water in the concrete mix freezes and all hydration reactions slow down. At temperatures below 0 ° C, chemically unbound water turns into ice and increases in volume by about 9%. As a result, stresses arise in the concrete, destroying its structure. Frozen concrete has high strength, but only due to the adhesion of frozen water. When defrosting, the cement hydration process is resumed, but due to structural disturbances, concrete cannot gain design strength, i.e. its strength is significantly lower than that of non-freezing concrete. Experiments have established that the hardening conditions significantly affect the process of concrete strength. If the concrete before freezing achieves 30-50% of the strength of the design, the further impact of low temperatures does not affect its physical and mechanical characteristics.

Strength, after a set of which further exposure to freezing does not affect the physico-mechanical characteristics of concrete, is called critical. The value of critical strength depends on the class of concrete.

When prestressed structures are erected, the critical strength of the concrete should be 100% design.

Thus, by creating favorable conditions for the hardening of concrete in the initial period, structures of the required quality are obtained.

The required temperature regime of hardening of concrete is created by various methods: by heating the concrete during its preparation, by keeping the concrete in insulated formwork (thermos method); the introduction of concrete chemical additives that reduce the freezing temperature; thermal effect on newly laid concrete heating forms; electrode heating; infrared heat sources. Technological technique is chosen taking into account the conditions of concreting, the type of structures, features of the concrete used, economic efficiency.