Concreting technology in winter conditions 7. Concrete is heated by infrared rays.

The source of infrared (heat) rays are heating elements with a power of 0.6 ... 1.2 kW with an operating voltage of 127, 220 and 380 V, ceramic rod radiators with a diameter of 6 ... 50 mm, power of 1 ... 10 kW, quartz tubular radiators and other means.

To create a directional flow of infrared rays used parabolic reflectors, spherical and trapezoidal type. Infrared installations, complete with reflectors and supporting devices, are used for heating structures erected in sliding formwork, thin-walled wall elements, floor preparation, slab structures, and joints of large-panel buildings.

When heating slab structures, radiators with box-type reflectors are used, which are either installed on a concrete surface or suspended at a distance from it. To prevent rapid evaporation of moisture, the surface of the concrete is covered with a film.

When building walls in panel and volume - adjustable formwork, one-sided heating with spherical-type radiators is used. To ensure the warming up of the entire plane of the wall, the reflectors are placed at different levels on telescopic racks and at the calculated distance from the wall.

During the erection of structures in a sliding formwork, the concrete coming out of the formwork is heated by a double-sided arrangement of infrared emitters. They are suspended from the formwork panels or placed on suspended platforms. To eliminate heat loss, the erected structures isolate the tarpaulin cover from the environment.

To warm up joints of precast concrete structures of large-panel buildings, various types of slats are used in the form of rectangular ducts (when making flat joints of elements) or segment (for joints located at right angles).

To improve the absorption of infrared radiation, the surface of the formwork is covered with black matte varnish. The temperature on the surface of the concrete should not exceed 80 ... 900C.

Infrared installations are placed at such a distance from each other to warm the entire surface of the concrete. Infrared heating provides good quality heat treatment of concrete, subject to the thermal conditions of curing concrete.