Winter requirements of work are determined by the average daily outdoor temperature below 5 ° C and the minimum daily temperature below 0 ° C.
To seal joints, the brand of concrete (solution) should be used one step higher than the means in the summer requirements.
Concrete (mortar) for sealing settlement joints must have a flattering temperature and be prepared using heated aggregates, as well as heated water. The water temperature cannot be higher than 60-80°С, and aggregates 40-50°С, with all this, the specified temperature of the mixture must be obtained, and not higher than 35-40°С.
The temperature of the mixture is specified based on regional requirements and the actual data on the heat loss of the mixture. Concrete (mortar) mixture should be given to the working area of the city in insulated boxes. The temperature of the concrete mixture prior to its heating must be at least 5 ° C. Directly before embedding, the surfaces to be joined are heated to a temperature of at least 10°C and not at all higher than 50°C. The approximate duration of heating the joint planes to a temperature of T0 ° C is 2-4 hours at outdoor air temperatures up to -10 ° C and 5-8 hours at outdoor air temperatures up to -20 ° C. Heating of a monolithic joint is carried out at a temperature of up to 50 ° C with a heating rate of 15 ° per hour. Temperature doubts at this time cannot be higher than 10 ° C, and the rate of cooling of the joint is 12 ° per hour. When heated by steaming, the temperature of the concrete can be increased up to 80°C.
The device of the pile foundations of houses does not urgently require the preparation of formwork, the pile foundation of the house is most of all what is needed for the construction of buildings using frame technology. On difficult soils, the most relevant is the use of bored or screw piles. Pile technologies for arranging the foundations of houses, different from monolithic ones, make it possible to significantly reduce the time frame for construction.
The heating temperature using electronic heaters is controlled by the automatic control design by turning off and connecting the power supply, and also by converting the amperage. The calculated joints loaded under the design load in the winter period of time are forced to be heated until 100% of the design strength of concrete at the joint is acquired and until 70% strength is acquired in other cases. In the joints of columns with glass foundations, in order to form a leveling layer in winter requirements, a mortar (concrete) of the same composition as in summer requirements should be used, but with the introduction of antifreeze additives.
Heating of joined elements before embedding is made: wire heaters made of nichrome (GOST 12766-67) and iron (GOST 3282-46) low-carbon wire with a diameter of 0.3-3 mm, located on an inexorable frame (for example, on an asbestos-cement sheet); tubular electric heaters (heaters) of serial production for air heating. When the column is fixed in the foundation glass for a short time due to the conductor, the frame of the wire heater is recommended to be scrupulously executed in the form of rectangular panels, the same size as the heated surfaces. The heaters are mounted in the joint cavity in such a way that the shield surface with the largest number of wire turns faces
foundation surface. The heating elements used for heating the joints are placed horizontally at any level, fastening along the height with wire twists.
If the short-term fixing of the columns in the foundation glass is made using wedges, then the frame of the wire heater is recommended to be scrupulously executed as corner shields. They will then adopt the heater as U-shaped tubes, which are placed vertically in the joint cavity. During heating, the joint cavity must be covered at the top with fireproof materials and insulated with mats made of mineral wool, straw, slag wool, etc. P. The joined particles have every chance of being heated by the feverish oxygen on the object with a temperature of 80-100 ° C, passed through an elastic sleeve, deeply lowered into the foundation glass.
For electric heating, electrodes made of whole steel with a diameter of 6-8 mm are inserted into the concrete of the embedment with might and main abyss of the glass at a distance of 200-250 mm between them. The distance between the electrodes must be performed with great accuracy, since those rejected by a certain number of centimeters significantly change the electronic power. The use of electrodes with an unclean plane also reduces the electronic power and worsens the developing disease of electrical heating, as a result of which they would like to be cleaned of rust and oil. The length of the electrodes is made similar, so that the part sticking out of the concrete is less than 5-8 cm. The ends of the electrodes due to conductors with a cross section of 1.5 mm2, a delicate iron wire with a diameter of 1-1.5 mm or an aluminum wire with a diameter of 0.5-1 mm are connected to the spotlights in a parallel cluster.
For temporary fastening of columns in a glass foundation, it is not recommended to use iron wedges to avoid local overheating and an unacceptable (another twenty percent) increase in power during electric heating of concrete. The surface of the laid concrete and the foundation during electrical heating are covered with mats of straw or slag, roofing felt, tarpaulin or other materials. Insulation is left after the current is turned off until the concrete cools down to 0 ° C. Electric heating should be constantly monitored by laboratory assistants and electricians on duty, who monitored compliance with the specified temperature regime.
When carrying out work on electrical heating, we follow scrupulously follow the orders given in the “Government for the electrical heating of reinforced concrete and concrete products and structures” (NIIZhB, 1964). The joint of the column must be heated to a temperature of at least 10°C and not higher than 50°C before embedding and caulking. For caulking a seam in winter, the same solution is used, as in summer requirements. The temperature of the mortar mixture in the first half of the caulking must be at least 10 ° C, and the concrete mixture for embedding in the first half of its heating – at least 5 ° C. The actual caulking lasts no more than half an hour; in this example, the joint surfaces do not have time to cool down. In one step, after caulking, the formwork is specified, the side planes are concreted and the concrete is heated. If the ends of the columns have cooled below 5 ° C, the concreting of the joints begins after their additional heating. It is preferable to caulk the seams with a cement-sand mortar of a 1: 1 composition with an additive of nitrite
sodium. Heating of the joint planes before caulking is then not performed. To avoid drying of the solution in the seam, the side surfaces of the joint are sealed not but there rather than on the next day after caulking.
Heating of joined elements and concrete of monolithic is made by contact heaters or radiators. Electric contact heaters are made of nichrome or low-carbon iron wire with a diameter of 0.8-3 mm and also, eat factory-made tubular electric heaters. Wire heaters are placed on a strong frame (for example, on an asbestos-cement sheet) or in a plastic sheathing (between two layers of fiberglass); Heating elements are mounted on an iron sheet.
The heater, together with thermal insulation, forms a thermal insert, which is attached to the iron shield of the inventory formwork. If there is steam or hot air on the object and not a very large amount of work using wooden formwork, heating of the joined elements and concrete can be done in regional greenhouses. If the outdoor temperature is -20°С, then the steam consumption per joint is on average 20 kg/h and the hot air consumption is 70-130 m3/h. It is also allowed to use opposite proven methods of heating, which ensure the acquisition of infused strength of concrete (mortar) of embedding Heating of the planes of the junction of rectangular cross-section crossbars with the column before embedding and concrete after embedding is carried out by contact heaters of the same design as for the joints of columns.
For the junction of the middle column with crossbars at an outdoor temperature of -20 ° C, the steam consumption is 25 kg / h, for frying the air – 200-300 m3 / h; for the joint of at least a column with a crossbar with a responsibly 10 kg/h c 100-150 m3/h. During heating, the joint cavity must be tightly covered at the top with a non-combustible substance (iron sheets) and insulated with slag mats, coordinating the redevelopment of real estate with mineral wool or other materials. The concrete for sealing the joint is still subjected to electrical heating, with all this, the joint cavity should be fenced off with a wooden formwork framed with steel corners. In the basement of the joint in the form of electrodes, rods with a diameter of 6-8 mm will be adopted, fastening the formwork panels and remaining in concrete after they are monolithic, and at the top of the joint – serviceable reinforcement. At the joints between the column and floor slabs, the concrete of the embedment is heated by floating electrodes, for which, immediately after compaction, rods with a diameter of 6-8 mm are installed in it.
