The pre-heated concrete mix, laid in winter conditions, is maintained primarily by a thermos method based on the use of insulated formwork with a device on top of a protective layer. Concrete mix with a temperature of 20 --- 80 ° C is placed in a warmed formwork, and open surfaces protect from cooling. It is not required to heat it, since the amount of heat introduced into the mixture during the preparation, as well as the physical and chemical processes of interaction of cement with water (exotherm) released as a result of it, is sufficient for its hardening and a set of critical strength. When designing a thermos curing of concrete, the type of formwork and the degree of its insulation are selected. The essence of the thermos method is that the concrete, cooling down to 0 ° C, can gain critical strength during this time. Given this, designate the thickness and type of insulation formwork. Warming formwork perform without gaps and cracks, especially in the joints of thermal insulation. To reduce the airflow through of the formwork and to prevent it from being wetted, a layer of toli is laid on the casing.
As a protective layer used roofing, cardboard, plywood, straw, which can be stacked sawdust, slag, slag, glass wool. The formwork can be double, then the gaps between its shields are filled with sawdust, slag, or filled with mineral wool, foam.
The formwork of reinforced concrete slabs is warmed from the outside by hanging mats on them. The surface in contact with the concrete is necessarily heated before the start of concreting. At the end of concreting, top open surfaces are immediately warmed, and the heat-engineering properties of this insulation (coating) should not be lower than that of the main formwork elements.
The formwork and insulation shall be dismantled upon reaching concrete of critical strength. The surface of the dismantled structure is protected from a sharp temperature drop to avoid the formation of cracks.
The thermos method is used for concreting massive structures. The degree of massiveness is estimated by the surface module Mn = F / V, where F is the area of the total cooled surface of the structure, m2; V- volume of construction, m3.
The design is considered massive when Mn <6, medium massiveness with Mn = 6 ... 9 and openwork with Mn> 9.
In determining Mn, the area of the surfaces of the structures in contact with the thawed soil, well-heated concrete surface or masonry is not taken into account. For long products and structures (for example, columns, crossbars, beams), Mn is determined by the ratio of the perimeter of their cross section to its area.
The thermos method is used for structures with Mn <6, and when concrete is preheated to 60 ... 800C - with Mn = 8 ... 10.
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