8589356467

Zh. Aymenov. HELIOTECHNICAL SYSTEMS AND PROSPECTS OF THEIR USE FOR "Z

CONCRETE

absence of a metal Container in the volume of helio chambers allows getting the air temperaturę much lower - 49-60 °C. Thus, one of the conditions of obtaining in helio chambers temperatures, close to the temperaturę of isothermal curing of concrete, is the presence of heat-sensitive materiał in the volume of helio-chamber. The disadvantages of these helio chambers are structural complexity, use of polished metal surfaces, and to reflect what has not found practical application of them.

To increase the level of employment of solar energy heat, rescarchers have suggested a system that combines a helio form and a helio bench that accumulate the energy of solar radiation separately, and at achieving the maximum temperaturę in the product the helio form and the helio bench combine. As a result, Products continue to harden in the thermos modę at night. Helio bench is a chamber with gratings of heat-accumulating walls of heavy concrete, from top it is coated with a translucent lid of SVITAP type. Helio benches allow gaining strength during total cure of 20-22 hrs. only of order 10-20% R₂g. This often results in products cracking, disarranges their structures.

There are various special helio chambers with polymeric film coating in which the "maturation "of reinforced concrete products takes place after the main stage of their thermal treatment morę often in curing rooms. Helping to lower the steam curing cycle by 30-40 %, however, this type of heat treatment of concrete has not found wide application, due to the overload of products after the incomplete cycle of steam curing in helio chambers with polymeric film coatings.

Helio treatment tumed out to be efiective also for gaining strength of polymer concrete and polymer mortar, which do not require moisture laden warming up. Solar energy should

advisably be useć irr «m-a: rt um walled polymer v    aer

self-heating is Iow.

Analysis of re^ear:! n 3 San :: e:: thermal treatment sbcws. seasonal. Therefore. me -■». :: :    er. le.

thermal treatment of    T-n-nw ;-or-

round operation of be bo esry    i*?

larger opportumties Tzz -additional source of thermal enerr>. r-raw n this case, is the electrical cacrr

As electric heating ciernej. 3    ■■ gjaę.

ones, as most commonly useć.    tc

considered: electrical cords. hear^z ferens. electrode heaters, etc. Elecmcal trz—-f elements have definite charac;er*ia:> nc specificity, reąuiring strict comrliazce :: accident prevention when using them. :> mainly well-made insulation of the hea^rs themselves, as well as obligatory groupdir.g :: definite parts of the unit. Therefore. me researchers were for a long time involved mtc the development of safer devices. using electrical energy. The first application of the heating equipment as contact heating-up of concrete refers to 1934. The construction. being concreted, was wrapped up in heat insulating mats with wire cages, to which current was delivered. Then engineer A. Vitkur offered a heating thermosetting formwork, in which as a heating element a spiral, wound along a layer of asbestos insulation on gas pipes, was used. “Heating bars” were in the form of bars of cement-sand mortar with section 25x25 mm and length of 400-500 mm with a Steel wire spiral 0.8 mm in diameter, embedded in them. However, these types of heating formwork and heating devices had serious drawbacks: labor intensity of manufacturing, ffagility and unreliability in operation, uneven heating of structures, high energy intensity.

DISCUSSION

This cxperience has given an impetus for the development of various types of electrical heaters: wire, tubular, rod, tape, netted, textile, woofed, carbon-fibrous ones.

The analysis of constructive Solutions of the existing types of heating elements and the experience of their application show that they have a number of drawbacks. Practically all above mentioned heaters are mounted in formworks, causing concentration of heat on the heat accepting surface directly beneath them and the temperaturę field in the heated surface is uneven. Also heat loss to the environment, the complexity of fixation, their prevention from damage, etc, are considerable._

Therefore, for modem heat treatment of products, using helio energy, it is necessary to choose such a type of electro conductive heating elements that would meet such requirements as: durability, water repellency, resistance to Chemical and mechanical effects of materials, having no adhesion to concrete, with a high coefficient of thermal conductivity (so that the temperaturę field in the volume of conductive part of the heater was maximally even),would have a smali heat capacity (the amount of energy for self-heating was minimal), would havc a high thermal resistance, sufficient for work at high temperatures - up to 90 °C.

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Journal oflndustriol Technology and Engineering, 2012, 2(3): 45 - 48