Humidity in the walls from aerated concrete for conditions northeast Asia

. The influence of the characteristics of external finishing coatings on the humidity regime in walls made of aerated concrete grades D350-D500 for buildings located in the geographic subregion of Northeast Asia has been assessed. The temperature of the onset of condensation has been determined depending on the type of finishing layer. The amount of condensed moisture in the fence in winter is calculated. The humidity regime in the walls was compared for the conditions of the Russian cities of Khabarovsk and Vladivostok, as well as for cities located in China close to the border with Russia - Beijing and Harbin. It has been established that the humidity regime of walls made of aerated concrete grades D350-D500, for the considered cities of China, to a greater extent, in comparison with the considered cities of Russia, depends on the characteristics of the external finishing coating.


Introduction
During the construction of buildings in various parts of the world, it is necessary to strive to reduce energy consumption during the further operation of these buildings [1][2][3].The norms for thermal protection differ significantly in different countries.Also, when designing enclosing structures, it is important to evaluate the humidity regime that will occur in them during operation.Moisture condensation occurs due to a significant difference in the vapor permeability and thermal conductivity of the materials used in the building envelope.To reduce the amount of moisture formed when moving from the inner surface of the fence to the outer surface, the vapor permeability of materials should increase, and the thermal conductivity should decrease [4,5].
This article explores the humidity regime in the walls of buildings during construction in the geographic subregion of Northeast Asia.Condensate is most harmful to fences and has the greatest destructive effect at negative outdoor temperatures.Therefore, given that the most severe conditions and the coldest winters in this region are observed in Russia and China, studies were carried out for cities from these countries.
In Russia, the heat-shielding qualities and the humidity regime in the walls for residential buildings located in the largest cities located in this subregion -Vladivostok and Khabarovsk were studied.When choosing cities for China, it was taken into account that this is a country on the territory of which a wide variety of climatic conditions are presented.According to the GB 50176 norms, the territory of China is divided into 5 zones, the division takes place according to the average monthly temperature in January and July.In the "Severe conditions" zone, the average monthly temperature in January is below -10 ºC, in the "Cold conditions" zone, the average monthly temperature in January is from 0 to -10 ºC, in the zones "Hot summer-cold winter", "Hot summer-warm winter", "Warm conditions" the average monthly temperature in January is above 0 ºC.Thus, zones with January temperatures below 0 ºC occupy more than half of the country's territory.For these zones, it is necessary to design enclosing structures taking into account not only the requirements for energy saving, but also taking into account the humidity regime inside the walls.The article investigates the heat-shielding qualities and humidity conditions in the walls of residential buildings located in the zones of China with "Severe conditions" (Harbin city) and "Cold conditions" (Beijing city).
Climatic parameters for these cities, used to perform heat engineering calculation and analysis of the humidity regime inside the fences, are presented in Table 1.The analysis shows that a significant part of residential buildings in Russia and China are built using aerated concrete.The widespread use of aerated concrete is due to its low thermal conductivity, high vapor permeability, relatively good performance properties, ease of masonry and high speed of construction of buildings from it.It is important to note that when using aerated concrete with a density of 300-600 kg/m 3 (grade D300-D600), singlelayer walls are built with good thermal protection performance.
In the course of the study, the humidity regime in the walls of aerated concrete was compared in pairs for Beijing and Vladivostok, and for Harbin and Khabarovsk.This division is due to the fact that the cities of Beijing and Vladivostok are characterized by rather warm winters.At the same time, the climatic conditions in Beijing are milder, the average temperature of the heating period t per is 2.6 °C higher and the average temperature of the heating period Z per is 74 days less.The cities of Harbin and Khabarovsk are characterized by colder winters, the average temperature of the heating period top for the city of Harbin is -10°С, for the city of Khabarovsk -9.5°С.Lime-sand plaster was used for the interior decoration of aerated concrete walls in the structure under consideration.Aerated concrete blocks with a density of 350 kg/m 3 and 500 kg/m 3 are taken as the main material of the wall.For exterior decoration of aerated concrete walls, three types of DBM were used: cement-sand plaster; Knauf GRUNBAND; limecement mortar filled with ash microspheres.The formulation of lime-cement mortar with a filler of ash microspheres was developed in the course of previous studies [6,7].When using these materials, one-layer walls can be obtained that comply with the current regulatory documents for thermal protection in Russia and China.Characteristics of materials are presented in Table 2.The thickness of the aerated concrete layer is determined by the calculation depending on the city and brand of aerated concrete In the course of preliminary studies, the minimum allowable thickness of aerated concrete blocks in enclosing structures was determined.The walls of the cities of Harbin and Beijing were designed taking into account the requirements of Chinese regulatory documents on thermal protection and in accordance with these materials [8].The walls of the cities of Vladivostok and Khabarovsk were designed taking into account the requirements of Russian regulatory documents for thermal protection.In total, 24 variants of enclosing structures were studied in the work.Structural features and thermal characteristics for buildings are presented in Table 3.To assess the probability of moisture condensation in the outer fences, we used a technique based on determining the temperature tc, at which condensation will begin to fall in the fence [9][10][11].

Research results
The results of the conducted studies comparing the humidity regime in the walls of buildings for the cities of Vladivostok and Beijing are shown in Fig. 2.
It has been established that despite the warmer winter, the humidity regime in the walls for the city of Vladivostok is more favorable.A significant difference between the temperatures of the onset of condensation t con.within the walls for the cities of Beijing and Vladivostok.So, when finishing walls made of aerated concrete grade D350 with cementsand plaster, the temperature of the onset of condensation t con for the conditions of the city of Beijing above the temperature of the onset of condensation t con for the conditions of the city of Vladivostok by 4.5°С.A significant difference in the temperatures of the onset of condensation t con in the walls of the cities of Vladivostok and Beijing is due to the fact that the normalized thermal resistance for the walls of the city of Vladivostok is 2.4 times higher.As a result, the thickness of the aerated concrete layer in the walls for the conditions of the city of Vladivostok is 0.25-0.35m higher.It has been established that when using the DBM developed for the conditions of the city of Beijing, the temperature of the onset of condensation t con 8.3 °C below the temperature of the onset of condensation t con in the walls using cement-sand plaster, and 6.4-6.9 °C below the temperature of the onset of condensation t con in the walls using the Knauf GRUNBAND DBM.It has been established that when using the DBM developed for the conditions of the city of Vladivostok, the temperature of the onset of condensation t con 3.7-6.1 °C below the temperature of the onset of condensation t con in the walls using cement-sand plaster, and 2.8-4.5 °C below the temperature of the onset of condensation t con in the walls using Knauf mortar GRUNBAND.
Summarizing the conducted studies, we can conclude that the thermal conductivity and vapor permeability of the finishing coating for the conditions of the city of Beijing has a significantly greater effect on the temperature of the onset of condensation t con within the walls compared to the city of Vladivostok.
An important step in the study of the humidity regime in building envelopes is the determination of the amount of condensed moisture that accumulates in the fence in winter.Considering that the temperatures of the onset of condensation t con above the average temperature for the heating period top only for the conditions of Beijing, when using D500 aerated concrete and cement-sand plaster, the amount of condensed moisture was determined only for this option.It has been established that the amount of moisture transferred from the inner surface of the fence to the condensation zone for the entire period of moisture accumulation for the year is 2.337 kg/m 2 , the amount of moisture transferred from the condensation zone to the outer surface is 1.821 kg/m 2 .Thus, the amount of condensate falling out for the entire period of moisture accumulation is 0.516 kg/m 2 , which will lead to an increase in the moisture content of aerated concrete over the entire thickness of the fence by 0.98%.This can significantly reduce the heat-shielding qualities of the fence and contribute to the destruction of the outer plaster coating.
The results of the analysis of the humidity regime in the walls of buildings for the cities of Khabarovsk and Harbin are shown in Fig. 3 Analyzing Fig. 3, we can conclude that the humidity regime in the walls for the conventional city of Khabarovsk is more favorable.This is due to the fact that despite the higher temperature of the heating period, the normalized thermal resistance for the walls of the city of Khabarovsk is 34.4% higher than the normalized thermal resistance for the city of Harbin.As a result, the thickness of the aerated concrete layer in the walls for the conditions of the city of Harbin is lower by 0.05-0.1 m.At the same time, it is important to note that when using the DBM developed, the temperatures of the onset of condensation in the walls for the conditions of these cities practically do not differ, the difference is no more than 0.5 °C.At an average temperature of the heating period top, no condensation will form in these fences.When using cement-sand plaster, the temperature of the onset of condensation t con 0.7-4.5 °С higher than the average temperature of the heating period top for the conditions of the city of Khabarovsk, and 2.2-6.5 °С -for the conditions of the city of Harbin.When using DBM Knauf GRUNBAND for the conditions of the city of Khabarovsk when finishing aerated concrete grade D350, the temperature of the onset of condensation t con above the average temperature of the heating period top by 3.0 °С, when finishing aerated concrete grade D500 -lower by 0.3 °С.When using DBM Knauf GRUNBAND for the conditions of the city of Harbin, the temperature of the onset of condensation t con above the average temperature of the heating period top by 0.9-4.9°C.Considering that the temperatures of the onset of condensation t con above the average temperature for the heating period top for 4 options for the city of Harbin and 3 warrants for the city of Khabarovsk, the amount of condensate was determined for all these options.The results of the study are summarized in Table 4.It has been established that the amount of moisture moving from the inner surface to the condensation zone for walls located in the city of Khabarovsk is lower than the value for walls located in the city of Harbin, provided that the density of aerated concrete is the same.This is due to the greater thickness of the walls for the city of Khabarovsk, and as a result, with a greater resistance to vapor permeability of the layers located from the inner surface to the condensation zone.
It was revealed that the increase in the moisture content of aerated concrete is significant (more than 0.1%) only in walls made of aerated concrete grade D350.In these walls, the use of cement-sand plaster or Knauf GRUNBAND DBM as an external finish can significantly reduce the heat-shielding qualities of the fences and contribute to the destruction of the external plaster coating.

Conclusions
It was revealed that in the single-layer walls of buildings made of aerated concrete grades D350-D500 in Chinese cities located in the "Severe conditions" and "Cold conditions" areas, conditions for the formation of condensate in the winter can be created.The results obtained are in good agreement with other studies on this topic [12][13][14].
It has been established that due to less stringent standards for thermal protection for newly erected buildings in China, a thinner layer of aerated concrete is acceptable, as a result of which more favorable conditions for the formation of condensate are created in the walls compared to Russian cities located in similar climatic conditions.Therefore, for the exterior decoration of aerated concrete walls for Chinese cities located in the "Severe Conditions" and "Cold Conditions" areas, it is very important to choose DBM, the finishing coatings based on which will have low thermal conductivity and high vapor permeability.The high efficiency of using lime-cement mortar with a filler of ash microspheres is shown.When using this DBM in all the fences under consideration, the temperature of the onset of condensation t con below the average temperature of the heating period t per .
It was revealed that the increase in the moisture content of aerated concrete is significant (more than 0.1%) only in walls made of aerated concrete grade D350.For these enclosing structures, the use of cement-sand plaster or Knauf GRUNBAND DBM as an exterior finish can significantly reduce the heat-shielding qualities of the fences and contribute to the destruction of the external plaster coating.

Table 2 .
Characteristics of the materials used in the considered enclosing structures.

Table 3 .
Structural features and thermal characteristics of the studied enclosing structures.

Table 4 .
Determination of the amount of condensing moisture and the increase in moisture content of aerated concrete.