GB2085425A - Heat and moisture treatment for building articles - Google Patents

Abstract

Building articles, e.g. concrete articles, are blown with an air agent having a temperature of from 40 to 100 DEG C e.g. in a predrying chamber 1 provided with air ducts 2 connected to an air screen manifold 3 located at the inlet of a tunnel chamber 3 and then are subjected in the tunnel chamber (3) to (a) temperature increase in zone (5) with a steam-air mixture for 1-6 hours, the temperature and humidity of the mixture being gradually increased to (b) isothermal curing in zone (6) for 2-6 hours with a heat- carrying agent having a temperature of 60-95 DEG C. and a relative humidity close to 100% and finally to (c) cooling in zone (7) where the articles are blown with a cooling agent having a relative humidity of 35-90% of 0.3-1.5 hours. <IMAGE>

Description

SPECIFICATION Heat and moisture treatment for concrete articles The present invention relates to the manufacture of building materials and, more particularly, it relates to a method of heat-and-moisture treatment of articles such as concrete articles and to an apparatus for accomplishing same.

This invention can be used in the industry of building materials, in civil, rural and industrial construction for manufacturing articles from heavy, cellular and ligh concrete, silicate, foamed concrete and gypsum, as well as other building materials which need to be heat-and-moisture treated after molding.

Presently known are the various method of heat-and-moisture treatment of concrete, reinforced concrete and other articles, including those involving zone and sectional temperature control; in particular, in a circular tunnel chamber when specific thermal conditions are maintained in each one of the sections (zones), with the articles being subjected at one of the steps to the effect of superheated steam and carbon dioxide gas and, at the next step, to the effect of steam, after which the articles are affected with air and then cooled.

However, said prior art methods and apparatus for accomplishing same provide for heat treatment without controlling the relative humidity of the medium at all steps of heat treatment.

While so doing, at the initial steps, upon the effect of superheated steam and then of steam with carbon dioxide gas, the continuity of the structure is disturbed considerably which leads to reduced strength. In addition, the use of the latter is rather difficult due to high capital costs.

There is also known a method for hardening and drying articles of light concrete, wherein the hardening of steam-treated articles is accelerated by using part of the steam extracted from said articles in the course of drying them with hot air.

Said latter method can only be used for drying light concrete articles and is absolutely inapplicable in the case of other types of concrete such as heavy concrete in view of dehydration and deterioration of all principal physical-and-mechanical characteristics of the latter.

There are further known methods of heat-and-moisture treatment of concrete articles, in particular, in a tunnel chamber with the aid of electric heaters attached to the inner walls of the chamber and serving to accelerate, by means of infrared radiation, the heat transfer to concrete, mainly ensuring the drying of the articles. Said latter prior art method suffers from considerable non-uniformity of heat-treatment conditions over the chamber zones and stages while the thermodynamic parameters of the medium (temperature, humidity, velocity) sometimes fail to satisfy the conditions of heat-and-moisture treatment. This leads to deterioration of physical and mechanical parameters of articles and results in that this method is mainly suitable for use in the manufacture of ligh concrete articles, which restricts considerably the sphere of its application.

Also known in the art are methods of steam-heat treatment, which involve the provision in the chamber zones of autonomous heating and recirculation systems involving the use of aerodynamic-effect power units with additional heaters, with a possibility of supplying steam to the working space.

Said and similar prior art methods suffer from difficulties in the discharge of steam-gas phase from concrete and in the control over the relative humidity of the medium and over mass transfer, also leading to degradation. This results in a lower quality of articles due to discontinuaton of the growth of concrete strength, as well as to reduced cold resistance, durability and other qualitative factors. Said latter method is only suitable for use with articles featuring a low modulus of exposed surface.

In view of the afore-listed disadvantages inherent in most of the above-cited prior art methods, further intensification of the process of heat-and-moisture treatment of articles becomes difficult and, in the case of some articles, simply impossible.

The problem of the invention is solved with the aid of a method of heat-and-moisture treatment of articles such as concrete articles, involving a zone control over temperature and humidity within the space of a tunnel chamber by way of temperature increase, isothermal curing of articles and cooling of the latter, wherein, according to the invention, prior to the step of temperature increase, the articles are blown with an air agent having a temperature of from about 40 to about 1 00 C. whereas in the zone of temperature increase the articles are affected with a steam-air mixture for a period of from 1 to 6 hours, the temperature and humidity of the mixture being increased gradually up to their permissible values corresponding to the given types of articles being treated while the articles in the zone of isothermal curing are affected for a period from 2 to 6 hours with a heat-carrying agent having a temperature of from 60 to about 95"C. and a relative humidity close to 100 % and in the cooling zone the articles are blown with a cooling agent having a relative humidity of from about 35 to about 90% for a period of from 0.3 to 1.5 hours.

The problem of the invention is also solved with the aid of an apparatus designed for accomplishing the method of the invention, including a tunnel chamber with zones of temperature increase, isothermal curing of articles and cooling of the latter, said tunnel chamber having an air screen manifold located at the inlet thereof, in which apparatus, according to the present invention, provision is made of a predrying chamber having air ducts and communicating by means of one of the latter with the air screen manifold.

It is expedient that the apparatus of the invention be provided with recirculation loops over all of the tunnel chamber zones, with a possibility of discharging part of the recirculate from the last one of said loops.

The herein disclosed method of heat-and-moisture treatment of articles resides essentially in ensuring an intensive and continuous flow of all of the basic hydration reactions while obviating the harmful effect of heat- and mass transfer processes, by way of zone control over the thermodynamic parameters of the medium (temperature and humidity), including the zones of temperature increase, isothermal curing and cooling of molded articles.

In so doing, the method is carried out such that an article, prior to the step of temperature increase, should be blown with an air agent having a temperature of from 40 to 100"C.; in the zone of temperature increase, the article is affected with a steam-air mixture for a period of from 1 to 6 hours, with the temperature of the mixture increasing (from 60 to 95 ) and maintained over the step of isothermal curing of articles, as to the relative humidity of the medium, it increases gradually over the step of temperature increase and, over the step of isothermal curing, maintains its value close to 100% for a period of from 2 to 6 hours.

While so doing, the articles in the cooling zone are blown with a cooling agent having a relative humidity of from about 35 to about 90% for a period of from about 0.3 to 1.5 h.

Following is a detailed description of a specific embodiment of the method according to the invention utilizing the herein disclosed apparatus for accomplishing same, with due reference to the accompanying drawing wherein: Figure 1 is a longitudinal sectional view of the apparatus according to the invention.

The apparatus for accomplishing the method of the invention is a continuous-action thermal unit including a pre-drying chamber 1. The end of said chamber 1 is communicated by means of air ducts 2 with a manifold 3 of the air screen of a tunnel chamber 4 having a zone 5 of temperature increase, a zone 6 of isothermal curing of articles and a zone 7 of cooling molded articles.

Each one of said zones is provided with preheat and recirculation loops with inlet and outlet pipes, respectively, pipes 8 and 9 for the zone of temperature increase, pipes 10 and 11 for the isothermal curing zone 6, and pipes 1 2 and 1 3 for the cooling zone 7. For moistening the medium in the zones of temperature increase and isothermal curing provision is made for the supply of steam via conduits 14 and 15.

Thus, the article is first directed to the pre-drying chamber 1 to which an air agent is supplied for treating the article surface therewith. Then, the spent air agent is transferred to the air screen manifold 3 of the tunnel chamber 4 to which the articles are delivered after the pre-drying chamber 1.

In the chamber 4, the articles pass successively the zones of temperature increase, isothermal curing and cooling of articles, where they are affected with a steam-air medium and steam featuring thermodynamic parameters corresponding to the stage of heat treatment. After being treated as described above the articles are moved outside of the tunnel chamber 4.

The present invention will be more apparent upon considering the following example illustrating the method embodying the invention.

Example A grade 200 concrete mix featuring a water-cement ratio of 0.35 and frustum shrinkage of 35 cm was used to mold a 1.5 x 6m plate; simultaneosly, check sample cubes were molded for heat-and-moisture treatment according to the disclosed method, for purely steam treatment according to a prior art method, as well as samples for natural hardening. The cubes together with the articles were subjected to heat-and-moisture treatment by moving them successively from the pre-drying chamber to the zones of temperature increase, isothermal curing and cooling wherein the articles and cubes had been affected with a steam-air medium featuring parameters such as those recited in the specification. The test results presented in Table 1 are indicative.of considerably improved characteristics as compared with prior art methods involving purely steam treatment of concrete, namely, increased strength and cold resistance, early hardening.

Table 1 Average Early strength, hardening MPa index 14.2 Disclosed method ---- 1.0 Ex. 23.0 Purely steam 11.2 0.67 treatment 23.5 Water absorption, Cold resistance Cold resistance factor, 50 cycles factor, 100 cycles 3.87 0.95 0.82 4.17 0.97 0.90 5.29 0.86 0.72 4.08 0.95 0.91 Note: Denominator gives the results of testing naturally hardened check sample cubes.

The foregoing data indicate that articles prepared with the aid of the method of the invention feature qualitative characteristics exceeding those yielded by purely steam methods of heat treatment, namely: -the strength increases by 10-20% and approaches that of naturally hardened concretes; -cold resistance increases, as well as the homogeneity of articles with respect to strength; -the duration of heat-and-moisture treatment of articles is reduced by 30-40%.

The reduction of the duration of heat treatment, as well as more efficient utilization of thermal energy supplied to the articles, results in a considerably lower steam consumption and, consequently, overall energy consumption.

Owing to the ease of manufacture and use, the method and apparatus of the invention can be used both under stationary and field conditions at moderate capital costs in acting enterprises and in those under construction.

The present invention helps produce diverse articles based on concrete of the various grades and types.

Claims (5)

1. A method of heat-and-moisture treatment of articles, for example, concrete articles, involving a zone control over temperature and humidity within the space of a tunnel chamber by way of temperature increase, isothermal curing of articles and cooling of the latter, the articles being blown, prior to the step of temperature increase, with an air agent having a temperature of from 40 to 100"C. Whereas in the zone of said temperature increase the articles are affected with a steam-air mixture for a period of from 1 to 6 hours, the temperature and humidity of the mixture being increased gradually up to their permissible values corresponding to the given type of articles being treated; the articles in the zone of isothermal curing being affected for a period of from 2 to 6 hours with a heat-carrying agent having a temperature of from 60 to 95"C. and a relative humidity close to 100% while in the cooling zone the articles are blown with a cooling agent having a relative humidity of from 35 to 90% for a period of from 0.3 to 1.5 hours.

2-. An apparatus for accomplishing the method according to claim 1, having a tunnel chamber with zones of temperature increase, isothermal curing of articles and cooling of the latter, and a chamber for pre-drying of articles provided with air ducts and mounted on said tunnel chamber, the latter chamber having at the inlet thereof an air screen manifold communicating with the chamber for pre-drying of articles via one of the air ducts of said predrying chamber.

3. An apparatus according to claim 2, wherein provision is made of recirculation loops over all of the zones of the tunnel chamber, with a possibility of discharging part of the recirculate in the last one of said zones.

4. A method according to any one of the preceding claims, substantially as hereinbefore described.

5. An apparatus substantially as hereinbefore described with references to the accompanying drawing.