Thermal conductivity of aerated concrete: what determines this indicator

Because of its lightweight and insulating qualities, aerated concrete is a widely used building material. Its thermal conductivity is one of the main reasons it works so well in construction. Having a better understanding of the factors influencing this attribute can aid builders in selecting more energy-efficient building materials.

The term "thermal conductivity" describes the capacity of aerated concrete to conduct heat. This characteristic is important because it establishes the material’s ability to insulate a building, keeping it cool in the summer and warm in the winter. It is crucial to take into account various factors when choosing aerated concrete for construction projects, as they have an impact on this indicator.

The aerated concrete’s density is a significant factor. Although a lower density typically translates into better insulating qualities, it can also have an impact on the material’s strength. The kind and quantity of additives added to the concrete affect its composition, which in turn affects how thermally conductible it is.

The moisture content is another crucial factor. Water can be absorbed by aerated concrete, increasing its thermal conductivity and decreasing its insulating power. Maintaining its insulating qualities requires careful handling and installation.

By being aware of these variables, contractors and homeowners can use aerated concrete in their projects with greater knowledge and assurance that the proper ratio between insulation and structural integrity is achieved.

Factor	Explanation
Density	Lower density aerated concrete has better insulation properties.
Moisture Content	Higher moisture levels can increase thermal conductivity.
Composition	Ingredients like lime, cement, and sand affect insulation efficiency.
Temperature	Extreme temperatures can alter thermal conductivity.
Age of Concrete	Newer aerated concrete may have different thermal properties than older blocks.
Manufacturing Process	Methods and conditions during production can impact the material"s thermal performance.

Brief characteristics of aerated concrete

Aerated concrete is a form of cellular concrete that is different from comparable wall materials in terms of how the pores are formed and the raw material composition. Even though it is comparable to analogues, there are instances when thermal conductivity and other characteristics diverge greatly.

You should first think about the specific qualities of the material in order to comprehend what can specifically affect changes in the numerical indicators of the characteristics.

Overview of the main properties and qualities

Principal attributes of air-filled concrete:

Characteristic name	Its average value
Frost resistance	35-150
Strength grade	For a non-autoclave – from B1.5, in accordance with GOST 21520-89; for autoclaved aerated concrete, on average – B3.5
Shrinkage	From 0.3 mm/m2
Minimum recommended wall thickness	From 0.4 m
Thermal conductivity	From 0.09
Environmental friendliness	2
Fire hazard	Does not burn

The qualities are highly competitive. All of them, though, vary within certain bounds and, as was already mentioned, are dependent upon specific circumstances. The minimum and average values are displayed in the table.

An aerated concrete block has a thermal conductivity of 0.09, which is typical only for dry thermal insulation products. Below, we’ll look at how it will alter as density increases.

Classification and scope of application

Given the subject matter of this article, it will be pertinent to comprehend the kinds of materials that are available. After all, a variety of factors affect the thermal conductivity of aerated concrete blocks.

Based on the hardening technique, an aerated concrete block can be:

Kindly take note! Synthetic hardening aerated concrete is another name for autoclaved aerated concrete. It varies in that it is subjected to high pressure and temperature during the last stage of production in an autoclave, a specialized piece of machinery. Consequently, the products exhibit improved properties, such as a higher density to thermal conductivity ratio. However, we will discuss this more later.

Hydration-hardened aerated concrete, or non-autoclaved products, naturally attains technical strength. According to GOST, the requirements for it are a little bit less. Let’s use the table to compare these aerated concrete types’ indicators.

A comparison of aerated concrete that has been autoclaved and that hasn’t

Name of the indicator	Value for autoclaved aerated concrete	Importance for non-autoclaved aerated concrete
Strength, grade	B2.5-5	B1.5-2.5
Frost resistance	35-150	15-35
Vapor permeability	0.2	0.18
Operational thermal conductivity	0.096-0.155	0.17-0.25
Fire resistance	Does not burn	Does not burn
Recommended minimum wall thickness, meters	From 0.4	From 0.65
Durability	Up to 200 years	Up to 50 years

You can see that, when it comes to practically every feature, synthetic aerated concrete outperforms non-autoclave in many ways. It should be mentioned that the latter can be made by hand and has a significantly lower price.

Moreover, aerated concrete is separated based on density.

This means that the content can be:

1. Heat-insulating. Such products are characterized by low density (up to 400) and thermal conductivity. They are used as a material for insulation, since the block is not capable of withstanding any significant loads.
2. Structural and heat-insulating aerated concrete has a higher density. The numerical indicator varies from 400 to 800. However, the thermal conductivity coefficient of aerated concrete blocks also increases. The material is used in the construction of walls and partitions.
3. Structural aerated concrete is the most durable of all. Its density is 900-1200. It can withstand significant loads, but at the same time, the walls require additional insulation, since the ability to maintain temperature in such blocks is quite low.

There are other classifications pertaining to the uniqueness of the product’s composition and appearance in addition to the ones mentioned above. Let’s have a quick look.

Aerated concrete can be: based on the type of binder.

• On a cement binder;
• On a lime binder;
• On a slag binder;
• On an ash binder;
• On a mixed binder.

This suggests that the main component’s content ranges from 15% to 50%.

Depending on the kind of siliceous element:

1. On sand;
2. On ash;
3. On other secondary industrial products.

Additionally, I would like to draw attention to the block’s geometric classification.

What is aerated concrete?

1. First accuracy category;
2. Second accuracy category;
3. Third accuracy category.

The category denotes potential geometric deviations, with GOST dictating the maximum values.

Crucial! The first category’s blocks are the most uniform; size variations shouldn’t be more than 1.5 mm. They are placed on a minimum-thickness layer of glue. And take note that this has a big impact on the overall thermal engineering of walls!

There are significant variations in the second category: up to 3 diagonally and up to 2 mm in size.

The third category of blocks is typically utilized in the building of outbuildings. Growing deviations require walls to be constructed with a solution that has a noticeably thicker seam. As a result, the room’s thermal conductivity and cold bridges are increased.

Kindly take note! Blocks belonging to distinct categories only differ in terms of geometric deviations. Technically speaking, there are no appreciable variations. There won’t be any differences in thermal conductivity, strength, frost resistance, or other indicators. The only way they can differ is if you compare products made by various manufacturers.

Aerated concrete is a popular building material known for its excellent thermal insulation properties. The thermal conductivity of aerated concrete, which determines how well it retains heat, depends on several factors including its density, moisture content, and the size of the air pockets within the material. Lower density and larger air pockets typically result in better insulation, making aerated concrete an efficient choice for energy-saving construction. Understanding these factors can help builders and homeowners choose the right type of aerated concrete for their projects, ensuring optimal thermal performance.

The concept of thermal conductivity and its meaning

A material’s capacity to hold its temperature is known as its thermal conductivity. For instance, if its coefficient is high, the building will rapidly cool down during the cold season and the cost of heating the room will rise dramatically. This is because heat will quickly escape to the outside.

Let’s assess the viability of using aerated concrete in this instance for wall construction or insulation.

Thermal conductivity of aerated concrete. Dependence of thermal conductivity coefficient on technical and mechanical parameters

GOST 25485-89 specifies the thermal conductivity coefficient of aerated concrete. Concrete with cells. Details. As previously stated, this indicator is directly influenced by the products’ density as well as the kind of silica component. Think about the table.

Thermal conductivity’s dependence on the type of silica component and the density of aerated concrete:

Type of aerated concrete	Strength grade	Thermal conductivity coefficient of aerated concrete made from ash	Thermal conductivity coefficient of aerated concrete made on sand
Thermal insulation	300	0.08	0.08
	400	0.09	0.1
Structural and thermal insulation	500	0.1	0.12
	600	0.13	0.14
	700	0.15	0.15
	800	0.18	0.21
	900	0.20	0.24
Structural	1000	0.23	0.29
	1100	0.26	0.34
	1200	0.29	0.38

The conclusion is self-evident: thermal conductivity increases with density.

• According to GOST, the manufacturer must take into account the fact that the thermal conductivity of products should not exceed the above readings by more than 20%.
• The table also shows that aerated concrete made with ash is more capable of maintaining temperature.
• Let"s take, for example, aerated concrete blocks d=600: their thermal conductivity coefficient is equal to 0.13. And for blocks of the same density, but made with sand, this indicator is 0.1 higher
• An important fact is that the thermal conductivity of the block significantly deteriorates when it is moistened. And since aerated concrete absorbs moisture quite strongly, it is worth paying attention to such changes.
• For example, the thermal conductivity coefficient of aerated concrete d500 is 0.12, but this is under standard measurement conditions. At operational humidity, this indicator increases by at least 0.2.

In other words, the thermal conductivity coefficient increases with increasing humidity. GOST states that when producing products on sand, the selling humidity of aerated concrete products should not be higher than 25%, and when producing products on ash and other secondary industrial products, it should not be higher than 30%.

It is worthwhile to consider materials like monolithic aerated concrete separately. It may also have varying densities and coefficients of thermal conductivity. This is mostly dependent on the porosity, component ratio, and brand of cement used in manufacturing.

It is employed actively in:

• Device screed. Monolithic floors made of aerated concrete are durable, the material is easy to handle. Often with its help they prepare the base for a warm floor.
• For roof insulation. In this case, a material of lower density is used.

Of course, there are a lot more potential applications for the material outside these few examples. It is still true that aerated concrete is becoming more and more popular every year, primarily because of its high frost resistance, density to thermal conductivity ratio, and other performance attributes.

Comparison of the ability of aerated concrete to retain heat with various wall materials

Let’s now examine the relationship between density and thermal conductivity, comparing aerated concrete’s value to that of other wall products. Does aerated concrete have a place among the best?

A comparison of aerated concrete’s and other wall materials’ technical and physical indicators

Name of material	Density kg / m3	Thermal conductivity coefficient
Aerated concrete	600-800	0.18-0.28
Silicate brick	1700-1950	0.85-1.16
Arbolite	400-850	0.08-0.18
Cinder concrete	900-1400	0.2-0.58
Foam concrete	400-1200	0.14-0.39
Expanded clay concrete	900-1200	0.5-0.7
Hollow brick	1500-1900	0.56-0.95

Indeed, upon comparing the aforementioned materials with aerated concrete, we find that the latter’s thermal conductivity marginally surpasses that of arbolite and foam concrete. It leaves other wall components far behind.

Low-density aerated concrete is utilized as an insulating material, as was previously mentioned. Now let’s compare how legitimately it can be used.

Comparing the thermal conductivity of materials meant for insulation to that of aerated concrete thermal insulation:

Name of material	Thermal conductivity coefficient, m2 * C / W
Heat-insulating aerated concrete, D300	From 0.08
Ecowool	0.014
Isover	0.044
Foam	0.037
Expanded clay	0.16
Glass wool	0.033-0.05
Mineral wool	0.045-0.07

Aerated concrete can be a competitive material even when it comes to heat insulation.

Developers frequently wonder which is better when selecting insulation: aerated concrete or expanded clay? It is really challenging to provide a clear response. It is important that you focus first on the indicators’ priorities. These materials are affordable, lightweight, and heat-retaining.

Heat-insulating aerated concrete still prevails in the final indicator, though, when the data shown in the table are taken into consideration. And you have the option.

Calculation of the optimal wall thickness

As we have already discovered, a wall composed of aerated concrete should have a minimum thickness of 400 mm. Nonetheless, there may be substantial regional variations with this indicator. The wall should be significantly thicker while still maintaining the ideal temperature in areas with lower air temperatures.

Let’s work out how to accurately compute the required wall thickness while accounting for all relevant variables, such as SNiP 23-02-2003 requirements. Building thermal protection, SP 23-101-2004 design of a building’s thermal protection system.

First, let’s look at what the thermal conductivity indicator will be (per SNiP) when manufactured with various silica components and final products placed in various solutions.

Computed thermal conductivity coefficients for the corresponding operating conditions A–B when building walls with mortar and glue:

Next, you need to figure out which humidity zone your area is in order to perform the calculations. The following table and the humidity zone map can be used for this:

Regional humidity regime:

Regime	Air humidity at a temperature of up to 12 degrees	Air humidity at a temperature of 12 to 24 degrees	Air humidity at a temperature of more than 24 degrees
Humid – 1	More than 75	From 60 to 75	From 50 to 60
Normal -2	From 60 to 75	From 50 to 60	From 40 to 50
Dry -3	Less than 60	Less than 50	Less than 40

You should now check SNiP 23-02-2003 to find out which operating conditions, based on humidity, the surrounding structures correspond to.

Conditions of operation for structures A and B based on local humidity levels:

Humidity mode	Operating conditions in the humid zone	Operating conditions in the normal zone	Operating conditions in the dry zone
Humid – 1	B	B	B
Normal – 2	B	B	A
Dry – 3	B	A	A

It is now worthwhile to go back to table 6, where the necessary indicator is located.

• For example, let"s assume that our region is Smolensk. Its territory belongs to the normal humidity zone – 2, indoor humidity is also normal, which means that in this case, the region is characterized by conditions B.
• Now we move on to calculations. We will need the value of the standardized heat transfer resistance. For Moscow, this is – 3.29.
• We will build a wall from blocks with a density of D500, laying will be done with glue. We find the required value in table 6. In this case, it is equal to – 0.23.
• Now we determine the thickness of the wall, for which we multiply the thermal conductivity coefficient and the resistance indicator heat transfer: 3.29*0.23=0.7567 meters.
• That is, in order not to violate SNiP standards, the wall thickness, under the above conditions, should be 0.76 meters!

Why, then, do manufacturers all agree that walls as thick as 400 mm can be installed, even though actual results vary? It’s easy!

First, as humidity varies during operation, aerated concrete’s thermal conductivity rises. Secondly, manufacturers neglect to account for cold bridges and other influencing factors when calculating indicators for product advertisements. In theory, walls can be thinner, but when insulating the structure, the difference in wall thickness must be made up in order to maintain the required thermal conductivity value.

You can learn more about how to maintain the ideal thermal conductivity quality indicator and insulate aerated concrete by watching the video in this article.

Overview of the main advantages and disadvantages of buildings erected from aerated concrete

Thus, in comparison to other materials designed primarily for wall construction, we have discovered that aerated concrete has a fairly good thermal conductivity coefficient. But there must be more than one debate when selecting goods.

Let’s quickly review the additional benefits that aerated concrete blocks offer:

1. The products are lightweight, which will significantly reduce the load on the foundation;
2. As mentioned above, the material is easy to handle, it is easy to saw, cut, and sand;
3. The composition of the aerated concrete block is an important aspect. It does not contain toxic or harmful substances for the environment, and therefore is environmentally friendly;
4. Aerated concrete does not burn and does not support fire. When ignited, it can be exposed to high temperatures for several hours;
5. High frost resistance. Products can withstand up to 150 defrosting and thawing cycles;
6. Vapor permeability will provide the most comfortable microclimate;
7. Soundproofing characteristics are also quite good. Aerated concrete walls can protect those in the room from extraneous noise from the outside;
8. Availability and prevalence of the material among manufacturers. This is also a significant plus. In almost any region, you can find a manufacturer or dealer located nearby. This will help save on delivery;
9. Variability of choice of sizes;
10. Another significant advantage is the ability to independently manufacture products. For those who want to save money or just try their hand – an excellent chance;

The primary drawbacks are:

1. High water absorption of the material. In this case, porosity is a negative side, especially at negative air temperatures. At this time, moisture can crystallize and have a destructive effect on the structure of the block.
2. Fragility of products. This is quite noticeable during work and transportation.
3. The shrinkage of the building has a place to be quite often and, as a result of this, as well as some other factors, cracks may appear.
4. The need to search and acquire special fasteners, and if desired, to fix particularly heavy objects, the need to plan and strengthen fixation nodes.

Method for testing thermal conductivity of products

GOST 7076 is followed in the application of the thermal conductivity control method, and GOST 10180 is followed in the sampling selection process. All of the information regarding the testing process, protocoling the results, and sampling technique is contained in documents.

The procedure basically involves creating a stationary heat stream and passing it through a sample with a chosen thickness. Its direction is opposite to the sample’s largest faces. Thus, the temperature of the sample’s face faces as well as its thickness and density of heat flow are measured.

The material certificate needs to specify how many samples are needed for testing. In the event that no such indication is present, five samples are used for the tests.

An overview of the steps involved in administering the test is provided here:

• Prepare the samples and the necessary equipment, according to the technical documentation;
• Place the sample in the device, previously calibrated;
• Every 300 seconds, measure the signals of the heat meter and temperature sensor;
• After establishing a steady heat flow, the thickness of the sample is subject to measurement;
• The final stage is to determine the mass of the sample.

Making wise choices in building projects requires an understanding of the thermal conductivity of aerated concrete. Building comfort and energy efficiency are greatly impacted by this attribute. Builders can achieve better insulation and energy savings by carefully considering the factors that affect thermal conductivity, such as density, moisture content, and the quality of the materials used.

The density of aerated concrete is a major factor in determining its thermal conductivity. Better insulation qualities are usually associated with lower densities because they have more air pockets that prevent heat transfer. To guarantee longevity and safety, it’s crucial to strike a balance between this and the building’s structural requirements.

Another important consideration is moisture content. Because aerated concrete absorbs moisture, its thermal conductivity may rise. Consequently, in order to preserve its insulating qualities, appropriate waterproofing and moisture control measures are required. This prolongs the life of the concrete and improves thermal efficiency.

Lastly, the thermal conductivity of aerated concrete is highly influenced by the caliber of the raw materials and the production process. A more consistent and efficient insulating material is produced by using premium ingredients and exacting production methods. Selecting reliable suppliers and manufacturers can have a big impact on how well the final product works.

In conclusion, builders can maximize the thermal conductivity of aerated concrete by taking care to ensure that it is the right density, moisture content, and quality. Because of improved insulation, increased energy efficiency, and increased building comfort, aerated concrete is becoming an increasingly important building material in modern construction.

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