Research of development and solution of problems of combined coverings of buildings

Volkova Ol'ga Vladimirovna Researcher, Siberian Federal University 660041, Russia, Krasnoyarskii krai, g. Krasnoyarsk, ul. Prospekt Svobodnyi, 82 volkova.olya13@mail.ru

Introduction

Combined coatings are the most economical and easy–to–install type of roofs, which simultaneously performs the function of a roof – protects from atmospheric precipitation, as well as the function of an attic floor - protection from temperature drop. Currently, it is necessary to make a rational choice of materials for the structure in order to increase the service life of the coating, to revise the method of roof reconstruction and the technology of its creation. This is due to the imperfection of the coating design due to savings in materials and the design development itself by reducing the cost of construction.

Relevance:

The relevance of the study is determined by the active use of combined coatings in residential buildings. This is due to the existence of a program that started back in the USSR at the beginning of 1970 for the construction and development of fully assembled housing construction, the type of roof of which was precisely combined coverings. From that moment to this day, there is a tendency to lose the performance characteristics of the coating after 3-5 years of roof operation. It is because of this that it is necessary to analyze the past experience of using building materials in the thermal insulation layer and the use of various alternative methods to increase the operational life of coatings. There is a need to create a coating that meets the requirements of durability, environmental friendliness and fire hazard for a comfortable life of people in houses with combined coatings.

In the works ^[2,7-8], the historical experience of the development and appearance of combined coatings is studied. Articles [3-6,16-17] present possible thermal insulation materials that increase the service life of the coating, as well as reduce the effects of precipitation on the construction of coatings. In this paper, the existing problems of coating and the historical experience of solving problems for the main periods of coating creation are considered and analyzed.

The purpose of the work: to identify the progressive development of scientific thought in solving technical problems of combined coating structures.

Research objectives:

- identification and analysis of the problems of the combined coating design;

- determination of the periodization of solving problems of combined coverage.

Subject of research: the history of the development of research and problems of the development of combined coating.

The research methods are used: from the point of view of applying solutions to various construction materials; from the point of view of applying a technological solution to the design problem.

The research methodology is based on a theoretical approach using methods of analysis, generalization, comparison, synthesis.

Study of the problems of the combined coating design

The experience of designing according to the large-panel construction program ^[12] showed that the main problems of operation of combined coatings were:

· climatic effects – increased humidity, increased density of the material and its destruction;

· subjective factor – violation of operation during construction, saving on materials.

The design of combined coatings should be accompanied by a thorough study of the initial construction data, namely, taking into account the temperature and humidity regime, the amount of precipitation of the selected construction area.

The main problems of the combined coating were and are:

1. Combined coatings remain unsuitable for different weather conditions. In the thermal insulation layer, natural condensation of moisture occurs throughout the year due to the closed structure of the coating (the insulation is located between the vapor barrier and the roofing carpet) and, as a result, the accumulation of moisture in the insulation. The amount of moisture directly depends on the duration of the period with negative temperatures (Krasnoyarsk = 169 days ^[20]), but during warming, evaporating, it cannot find a way out and penetrates under pressure under the roofing carpet, thereby tearing it from the base. The particles of the moisture that has not come out freeze when negative temperatures occur and the roof turns into an icy air cushion. The insulation loses its properties, puddles appear on the roofing carpet, cracks appear.

2. In residential buildings, the vapor barrier over rooms with high humidity conditions in places adjacent to sewer pipes does not completely protect the structure due to the inability to fully seal the joints and part of the water vapor enters the insulation. Due to the smaller number of wet rooms, public buildings feel this phenomenon less.

3. When carrying out repair work, it is impossible to replace one of the layers of the coating structure due to getting wet, since during operation all the water will enter the apartments and flood them.

4. The subjective factor. During construction in adverse weather, precipitation can get into the coating and cause moisture accumulation.

To solve problems in each historical period, a different method of development was used, based on the available material and labor resources. We will consider these solutions in the next part in more detail.

Retrospective study of the history of solving problems of combined coverage, periodization (stages)

A retrospective study of the history of the combined coating, the popularity of which was formed due to the USSR program, was carried out thanks to several historical stages (Fig. 1), characterizing the meaningful development of solving the problems of this design.

Figure 1 – Historical development of solving problems of combined coverage, periodization (stages): scheme

Stage 1. 1970 – 1990

The first materials used in combined coatings were rolled waterproofing materials – most often roofing material, as well as expanded clay served as insulation. Over time, expanded clay lost its thermal insulation qualities by means of moisture absorption, which led to a decrease in the heat transfer resistance of the structure, and the roofing material turned out to be short-lived, which led to problems in operation, such as swelling and tearing of the material, its detachment in places of gluing to the parapet. Because of this, in the first houses built after 5 years, the roof lost its operational properties, and by 1990 the volume of roofs requiring repair amounted to 140 million m2.^[12] In order to restore the roofing, more than a quarter of the rolled materials produced were required. At the same time, it was decided to carry out repairs with the help of stickers of additional layers of rolled waterproofing material in areas of roof leakage, so as not to dismantle the entire roof ^[2]. It is worth noting that this repair lasted 10-12 years, later it took a major repair of the roof ^[3.21].

Stage 2. 1990-2000

A change in the technology and operation of the work on the production of combined coatings has made the transition to the mass use of surfaced insulated rolled water insulation materials with a factory protective coating instead of a protective layer of the roof (Fig. 2). This technology has reduced the process of repairing the roof and increased its service life, since the previous repair was not suitable for this design. However, the new technology did not last long, after 5 years half of the combined insulated rolled roofs had to be changed. Cracks and leaks appeared on the roof in the upper roll of the waterproofing carpet, which also formed condensation in the insulation and negatively affected the lives of people in houses with damaged coatings.  It was because of the protective sprinkling instead of the protective layer that cracks appeared on the coating. Because of this problem, it becomes urgent to increase the operation of combined roof coverings due to the refinement of rolled coverings, without providing roof repairs, since this is a labor-intensive technical process that may not be available due to the closed structure. It is the roof leaks that are the most noticeable defects of all, which causes material damage to residents.

Figure 2 - Construction of a combined coating with direct placement of layers: 1 – waterproofing carpet (3-4 layers of surfaced roofing material, top layer with factory protective sprinkling); 2 – non–combustible plate insulation (mineral wool slabs); 3 – layer of pasting vapor barrier; 4 - leveling screed (cement–sand), roof slope (expanded clay gravel); 5 - load-bearing structure of the coating (reinforced concrete slab) ^[4]

Stage 3. 2000 - present

In this period, the solution of the problems of UV radiation exposure to rolled waterproofing material is solved through the use of protective sprinkles - a roof element that protects rolled materials from mechanical damage, atmospheric influences and other destructive actions. However, as recent studies have shown ^[4], after 5-6 years, the protective layer is destroyed in areas with a large slope, which proves the flaw of this constructive solution.

Using the example of a public building ^[8], a positive effect was revealed due to such a technological solution as the installation of aerators. This device is designed to remove condensate from the thermal insulation layer.

In recent years, when repairing rolled roofs with a combined coating, thermomechanical treatment of a waterproofing carpet is used, which is based on the restoration of bitumen materials (Fig.3) ^[16]. During the reconstruction process, the material is heated by a special device and at the end of the process, a thermal insulation layer is arranged. Thermal insulation of such roofs is made of mineral wool slabs, tightly adjacent to each other. After completion of the work on the thermal insulation device, PVC membranes are fixed using the heat-welded method. At the moment, this method is effective and is the most reliable of all existing ones.

Figure 3 – Scheme of reconstruction of the combined coating structure:

1 – PVC membrane waterproofing carpet; 2 - thermal insulation layer of mineral wool slabs; 3 – rolled waterproofing carpet (existing); 4 – cement–sand screed (existing); 5 - a layer of expanded clay gravel along the slope (existing); 6 – a layer of thermal insulation (existing); 7 – reinforced concrete multi–hollow plate coatings (existing) ^[6].

It is worth noting that despite the different methods in each specified period, currently various organizations continue to apply the solutions described in the first stage of periodization, and in the second, not paying attention to the developed recommendations ^[6] and methods of solving problems. These methods do not solve all the problems of combined coating and further development of constructive coating ideas is necessary, but, however, the main factor in solving problems remains the expenditure of large funds on the materials used and the structure itself, which will not dramatically affect the construction. Currently, all materials have improved components, technologies and additives used, based on this, it is necessary to analyze and revise the combined coating in order to identify the most suitable and suitable for long-term use materials.

Conclusions

The problems of the combined coating design from 1970 to the present are analyzed. The analysis showed that the most important problems of the coating were and are: precipitation, which destroys the roll layer, penetrates the thermal insulation and creates condensation due to the closed "pie" of the structure; the subjective factor is the desire to save on materials, to do work in adverse weather conditions (rain, snow).

The main periods of change of the combined coverage are revealed. Methods of solving design problems have been developed for each period, both with the use of various materials and with the use of technical means. The technologies and materials used were effective for a certain period of time, protected from precipitation and temperature changes, but after a few years they failed. Despite the considerable experience of using this design, it is necessary to agree on the need to improve it, taking into account the different temperature characteristics of the construction areas, as well as the use of higher-quality materials of the upper coatings.

Conclusion

In all historical periods, new materials and technologies are being developed and introduced into construction to improve the combined coating, but there are still significant negative factors that weaken the roof and affect its performance.