Thermal conductivity of aerated concrete (aerated concrete blocks): what it depends on, improvement of characteristics

Because of their lightweight design and ability to insulate against heat, aerated concrete blocks are becoming more and more common in the construction industry. These blocks are a particular kind of concrete that has had air bubbles added to it, making it less dense and more energy-efficient. Aerated concrete’s thermal conductivity must be understood in order to assess how well these blocks keep buildings cool in the summer and warm in the winter.

Aerated concrete’s heat conductivity is contingent upon multiple factors, such as the block density, the size and arrangement of air bubbles, and the moisture level. Better insulation is typically found in lower-density blocks with more air bubbles in them. But since wet blocks conduct heat more effectively than dry ones, moisture can have a big effect on how insulating they are.

Optimizing these variables is necessary to increase the thermal conductivity of aerated concrete. To improve insulation performance, manufacturers never stop experimenting with different production processes and mix compositions. Improved control over the size of the air bubbles, mixing modifications to lessen moisture absorption, or adding extra insulating materials are a few examples of innovations. These developments contribute to the continued effectiveness and energy efficiency of aerated concrete as a building material.

Brief characteristics of aerated concrete

Although aerated concrete manufacturing technology has been around since the turn of the century, its actual application in construction dates back only a short while.

The well-known pores in concrete are created by the reaction of lime and aluminum powder. This chemical reaction releases hydrogen into the cement, causing the cement to become porous. These pores, which are uniformly spaced throughout the block’s surface, give the substance new qualities uncharacteristic of concrete.

It is crucial to take these qualities into account.

Overview of the main properties and qualities

The light weight of aerated concrete is its most advantageous feature. Aerated concrete will weigh significantly less than simple concrete when two identical blocks are compared. Low heat conductivity and vapor permeability are two beneficial properties.

Less energy will be used to heat the building because a block with more pores will release heat more slowly. Aerated concrete has open pores, whereas the pores in foam concrete are closed. This is evident when comparing the two porous materials. As such, the density of the latter is lower than that of aerated concrete.

Classification and scope of application

Groups of aerated concrete are separated based on density. Density is a property that has an expression of kg/m³.

1. D300-D400. Used for thermal insulation. Blocks of this grade are called thermal insulation.
2. D500-D900. Widely used in cottage construction. Used for insulation of 1-story houses. These blocks are called structural and thermal insulation.
3. D1000-D1200. Used to create walls of multi-story buildings. Called structural.
4. D600 means that 1 m³ of such concrete contains 600 kg of solid material. This will be only a third of the entire volume of the block. The rest of the volume will be air.

Advantages and disadvantages

Aerated concrete becomes more brittle than more densely packed building materials because of its porous structure. However, this building material’s primary drawback is that it is hygroscopic.

In certain situations, actions must be done to reduce the undesirable aspects. For instance, aerated concrete slabs have reduced humidity and blocks are waterproofed.

The concept of thermal conductivity and its significance

Heat cannot escape from the cells because of the slow heating of the air inside. The thermal conductivity decreases with decreasing density. The ability of a building material to transfer heat is implied by the concept of thermal conductivity.

The constructed home will cool down more quickly in low ambient temperatures the higher the thermal conductivity of the aerated concrete. It turns out that blocks D300, D400 will have a lower indicator than blocks D500, D600 if we compare the grades of aerated concrete by thermal conductivity. GOST determines the coefficient for various grades of aerated concrete.

For instance, the aerated concrete’s coefficient of thermal conductivity for D300 and D500 blocks will be 0.08 and 0.1, respectively. The indicator for grade D1200 will be 0.29.

Dependence on density

The building material’s capacity to conduct heat is significantly influenced by its density. The thermal conductivity of a wall with the same thickness but different materials will vary.

Dependence on humidity

Variations in thermal conductivity during block manufacturing are permitted, but they shouldn’t exceed 20%. It should also be kept in mind that the value shown in the tables is derived under ideal circumstances and does not account for environmental factors like air humidity. As air humidity rises, so does thermal conductivity.

The blocks will inevitably come into contact with the surrounding air when building a house. Although water does not absorb well in aerated concrete, this does not mean that water cannot still affect the material. As a result, the values for thermal conductivity are less than the reference values.

The blocks may have up to 10% humidity. When D500 blocks are exposed to high humidity, their thermal conductivity will rise by an average of 0.2 W/(m °C). Experts say that this is not very much.

Dependence on the quality of the macrostructure

Voids have an impact on more than just gas block strength. They use this material to ensure minimal heat loss. The manufacturing technology affects the product’s structural characteristics. In this instance, the size of the voids affects the thermal conductivity. Less heat loss occurs in materials with a higher void content. When selecting a brand, this should be considered.

Thermal conductivity coefficient for the D600 brand

This particular brand of aerated concrete has an average thermal conductivity coefficient of 0.14 W/(m °C). We need to take steps to waterproof this material so that it can retain heat more effectively. However, once the house is built, the iron reinforcement in addition to the blocks emits heat. The blocks then need to be installed using glue.

Coefficient for grade D500

This grade has a coefficient of 0.12 W/(m °C). In this regard, the aerated concrete bears the closest resemblance to the brick indicators. As a result, walls for apartment buildings may be constructed out of it.

Comparison of aerated concrete for heat retention with various wall materials

For a brick wall to have the same thermal conductivity as an aerated concrete wall that is 44 cm in length, the wall’s thickness needs to be many times larger, or exactly 210 cm. The brick emits more heat because of its higher density.

• brick – 0.35 W/(m °C);
• aerated concrete grade D400 — 0.10 W/(m °C).

As per established norms, a 44 cm aerated concrete wall’s thermal conductivity is equivalent to walls composed of:

• expanded clay concrete (90 cm);
• wood (53 cm);
• mineral wool (18 cm);
• polystyrene foam (12 cm)

The outcome is evident when selecting an aerated concrete block over brick.

Calculation of the optimal wall thickness

Red brick and sand-lime are frequently used as comparisons for aerated concrete blocks. And they make an effort to connect these materials’ attributes to the traits and markers of an aerated concrete wall. In addition, they overly thin them by depending on the walls’ low heat conductivity. Instead, they end up with a house that loses a lot of heat.

As a result, specific guidelines controlling the thickness of aerated concrete load-bearing walls were created. Simultaneously, they consider the level of moisture absorption by aerated concrete in addition to its thickness. According to SNiP, factors like the structure’s resistance to heat transfer are taken into consideration when determining the wall thickness. This characteristic is dependent on the thermal conductivity coefficient and the area in which the construction is being done.

Regarding the first value, the material’s resistance, there will be significant regional variations in its values, particularly when comparing areas like Moscow and Magadan.

For instance, the thickness of walls constructed with D500 gas blocks will be 35 cm in Moscow, 45 cm in Novosibirsk, and 65 cm in Yakutsk.

Following the golden mean rule will result in an excellent ratio of the wall’s strength and thermal conductivity, among other indicators. These are the characteristics of blocks D500-D600. They are most frequently utilized in the construction of other buildings, including cottages and residential structures.

Method for testing the thermal conductivity of products

Concrete blocks with air inside are practical and long-lasting. However, it’s important to consider every aspect of the building material, including heat transfer, before beginning construction. Each of these traits will be connected to the building’s operational circumstances. As a result, calculations are made regarding the walls’ strength and heat-conductive capacity.

The thickness of the walls is only determined after the strength classes and thermal conductivity of the aerated concrete blocks have been determined through testing. Additionally, the thermal conductivity indicators are contingent upon the building’s intended use.

Factor	Impact on Thermal Conductivity
Density of the Blocks	Higher density blocks usually have better thermal conductivity because they have more material to conduct heat.
Size and Shape of the Blocks	Larger blocks with fewer joints can improve insulation by reducing the number of heat transfer points.
Type of Aeration	The type and amount of air bubbles in the concrete affect its insulating properties. More air bubbles generally mean better insulation.
Moisture Content	Moisture can increase thermal conductivity. Keeping blocks dry helps maintain their insulating properties.
Surface Treatment	Special coatings or treatments can enhance the insulation by creating a barrier to heat flow.

In conclusion, one of the most important factors influencing aerated concrete’s effectiveness as a building material is its thermal conductivity. The precise makeup of the blocks and the amount of air inside them determine how insulating they are. Since air is a poor heat conductor, the more air that is trapped inside the blocks, the better their thermal insulation. How effectively these blocks can insulate against temperature changes is also determined by a number of important factors, including the kind of raw materials used and the manufacturing process.

Increasing production methods and mix optimization are common ways to improve the thermal performance of aerated concrete. Blocks with even better insulating qualities can be achieved by adding additives or modifying the mix’s proportions. As production techniques and materials continue to evolve, aerated concrete is becoming a more and more viable choice for energy-efficient building.

In the end, increasing the thermal conductivity of aerated concrete not only improves building comfort but also helps with sustainability and energy savings. We can anticipate even more improvements in the functionality of these adaptable building blocks as technology develops, which will help satisfy the rising demand for ecologically friendly and energy-efficient building solutions.

Known for their insulating and lightweight qualities, aerated concrete blocks’ thermal conductivity varies depending on the type of aeration utilized, density, and moisture content. Enhancing these qualities requires optimizing the material composition and production method to increase insulation without sacrificing structural integrity. This article examines how these variables affect thermal performance and offers suggestions for improving aerated concrete’s energy efficiency in building.

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