How to determine the thermal conductivity of concrete and what it depends on?

The world’s most popular building material, concrete is known for its strength and longevity. However, for applications where energy efficiency and temperature control are critical, comprehending its thermal properties is essential. The way concrete behaves in various settings is greatly influenced by its thermal conductivity, which is a measurement of a material’s capacity to conduct heat. Architects and engineers can plan construction projects more intelligently if they understand this property and the factors that affect it.

There are several approaches to determining the thermal conductivity of concrete, and each has benefits and drawbacks of its own. Two popular methods are the transient method, which evaluates temperature variations over time, and the steady-state method, which measures thermal flow through the material. These tests provide important information for engineering and construction by determining how quickly and efficiently concrete can transfer heat.

There are multiple factors that affect concrete’s thermal conductivity, such as its composition, density, and moisture content. Aggregate types, like crushed stone or gravel, can have a big impact on conductivity. Furthermore, the way heat moves through concrete can be changed by the air pockets that exist within it, which are frequently impacted by the density and mixing technique of the material. Additionally, moisture is important because water conducts heat differently than dry materials, which has an impact on the concrete’s overall thermal behavior.

Optimizing building designs requires a thorough understanding of the subtleties of concrete’s thermal conductivity, especially in regions with drastic temperature swings. Engineers can improve a building’s comfort and energy efficiency by choosing the ideal combination of materials. By carefully examining the variables that impact thermal conductivity, concrete structures’ performance can be adjusted to satisfy particular functional and environmental requirements.

How does the thermal conductivity of concrete affect the indoor microclimate

Concrete is one of the most often used building materials when it comes to building construction. The concrete’s thermal conductivity coefficient is one of the material’s primary performance attributes. In order to enable the construction of a residential building from the erected reinforced concrete structure, thermal insulation materials must be included in the design phase of the project. After all, it’s critical to create good living conditions in addition to constructing a sustainable, unique, and eco-friendly building.

By selecting the appropriate thermal insulation materials and being aware of the concrete massif’s thermal conductivity, you can accomplish noteworthy outcomes:

• significantly reduce heat loss;
• reduce the cost of heating the premises;
• ensure a comfortable microclimate inside the building.

A straightforward relationship describes how the thermal conductivity level affects the interior microclimate:

• as the coefficient increases, the intensity of heat transfer increases, and a building erected from a material with such characteristics cools down faster and, accordingly, heats up at an accelerated rate;
• a decrease in the ability of the concrete mass to transfer heat allows you to maintain a comfortable temperature inside the room for an extended period of time, with a corresponding reduction in heat loss.

In summary, one of the key elements influencing a home’s comfort is the concrete’s level of thermal conductivity. The mass structure of various types of concrete varies, as do the filler’s characteristics and the material’s level of heat conductivity. In order to guarantee that the concrete mass will consistently retain heat in the space, it is crucial to use these concrete grades in conjunction with insulation materials. During the design phase, the selection of building materials is made.

Thermal conductivity of reinforced concrete and thermal resistance – getting acquainted with the concepts

The following features that guarantee the building’s energy efficiency should be taken into consideration when choosing whether to use a particular brand of concrete or other building material:

• thermal conductivity coefficient of reinforced concrete or concrete. This is a special indicator that characterizes the volume of thermal energy that can pass through various building materials in a certain period of time. With a decrease in the value of the coefficient, the ability of the material to conduct heat decreases, and with an increase in the indicator, the rate of heat removal increases;
• thermal resistance of building structures. This parameter characterizes the properties of building materials to prevent heat loss. Thermal resistance is an inverse indicator when compared with the degree of thermal conductivity. With an increased value of the thermal resistance indicator, the building material can be used for thermal insulation purposes, and with a reduced value – for accelerated heat removal.

These indicators must be considered when creating a project for a future building and doing thermal calculations.

For concrete to function as best it can in building applications, its thermal conductivity must be determined because it affects the material’s ability to insulate and regulate temperature. The concrete’s composition, density, moisture content, aggregate and air void content, and other factors all affect this property. Engineers and builders can adjust concrete mixes to meet specific energy efficiency and structural requirements by measuring thermal conductivity. By having a better understanding of these dependencies, construction decisions can be made to create buildings that are both occupant-friendly and energy-efficient.

Thermal conductivity coefficient of concrete for various types of monolith

It is important to consider how the variations in concrete affect the monolith’s thermal conductivity when choosing the type that will be used to construct a residential structure. will be useful in comparing the concrete table’s thermal conductivity, which includes all of the properties of each type of concrete. Think about the variations in the concrete array’s thermal conductivity, which is expressed in WT/m 2 x ºC for the most common material varieties.

The coefficient’s lowest value was found in concrete composites with cellular structures:

• For dry foam concrete and gas -filled concrete, the value of the indicator is small, compared with other types. It increases with an increase in the density of the material. With a specific grade of 0.6 t/m 3, the coefficient is 0.14, and at a density of 1 t/m 3 already 0.31. With basic humidity, the values ​​increase from 0.22 to 0.48, and with 0.26 to 0.55 increased;
• Keramzitona -filled concrete, depending on the density of the array, also has a different coefficient value that changes in proportion to the increase in specific gravity. So expanded clay concrete with a density of 0.5 t/m3 has a low coefficient equal to 0.14, and with an increase in density to 1.8 t/m3, the thermal conductivity parameter increases to 0.66.

The filler utilized to prepare the concrete mixture also affects the coefficient’s value:

• for heavy concrete with a density of 2.4 t/m3, containing crushed stone filler, the indicator is 1.51;
• concrete, where slag is used as a filler, is characterized by a reduced thermal conductivity of 0.3–0.7;
• expanded clay concrete containing quartz or perlite sand has a density of 0.8–1 and, accordingly, a thermal conductivity level of 0.22–0.41.

Firmly insulate the structure that is being built. The use of a thin layer of thermal insulator is necessary when building walls out of porous concrete with low thermal conductivity. When using heavy grades of concrete, the building’s insulation must be improved. A substantial layer of thermal insulator is applied for this. The fact that the concrete mass’s thermal conductivity rises with density should be considered when choosing a material.

What factors affect the thermal conductivity coefficient of reinforced concrete

Regardless of the brand and whether steel reinforcement is present in the array, a number of factors affect how thermally conductive concrete is. Now let’s look at the indicators, each of which affects this attribute differently:

• structure of the concrete array. When creating air cavities inside the monolith, the process of heat transfer through the cellular array is carried out at a low speed and with minimal losses. To summarize, an increased concentration of cells allows reducing heat loss;
• specific gravity of the material. The density of the concrete array affects its structure and, accordingly, the intensity of the heat exchange process. As the density of the material increases, the degree of heat transfer increases and the volume of heat loss increases;
• moisture concentration in concrete walls. A concrete mass with a porous structure is hygroscopic. Moisture particles that penetrate deep into the concrete through capillaries fill the air pores and thereby accelerate the heat transfer process.

It is important to consider that less heat is lost and the material’s degree of thermal conductivity decreases with decreasing humidity when performing calculations. By using porous filler, it is possible to lower heat loss and create a cozy interior microclimate. It is best to use low-therm conductivity building materials for thermal insulation. By understanding how the properties of concrete affect its heat conductivity, you can select the best kind of material to use for walls.

Thermal conductivity of concrete and insulation of buildings

The choice of concrete types for wall construction determines the thermal insulation of the walls of buildings that are currently under construction. The types of concrete products are as follows:

• structural, used for capital walls. They are distinguished by increased load-bearing capacity, increased density, and the ability to conduct heat at an accelerated rate;
• thermal insulation, used in unloaded structures. Characterized by reduced specific gravity, cellular structure, due to which the thermal conductivity of the walls is reduced.

Different types of concrete can be used to build walls and keep the room at a comfortable temperature. The walls’ thickness will differ greatly in this situation. The following thickness of capital walls ensures the same level of thermal conductivity:

• foam concrete – 25 cm;
• expanded clay concrete – 50 cm;
• brickwork – 65 cm.

Thermal insulation of building structures is done as part of energy-saving measures to maintain a favorable microclimate. During the project development phase, experts identify potential pathways for heat loss and choose the most effective insulation solution.

The following building components’ inadequate thermal insulation accounts for the majority of heat loss:

• floor surface;
• main walls;
• roofing structure;
• window and door openings.

You can save a lot of money on heating and improve the comfort level of your house with the help of an expert installation and high-quality insulation.

How is the calculation made taking into account the thermal conductivity coefficient of concrete

Modern buildings’ load-bearing walls are constructed with multiple layers, including capital structures, thermal insulation materials, and finishing coatings, to ensure a comfortable temperature and minimize heat loss. There is a specific thickness for each layer in the sandwich.

The thermal resistance formula, R = p / k, must be applied in order to solve the problem of determining the heat insulator’s thickness. This formula can be interpreted as follows:

• R is the value of temperature resistance;
• p is the value of the layer thickness, indicated in meters;
• k – coefficient of thermal conductivity of reinforced concrete, concrete or other material from which the walls are made.

You can independently complete the calculation with a standard calculator by using this relationship. This can be calculated by dividing the building structure’s thickness by the concrete or other material’s thermal conductivity coefficient. Now, let’s look at a calculation example for 0.3 meter thick walls made of aerated concrete that has a specific gravity of 1000 t/m3 and a thermal conductivity of 0.31.

Algorithm for computation:

• Calculate thermal resistance by dividing the thickness of the walls by the thermal conductivity coefficient – 0.3: 0.31 = 0.96.
• Subtract the obtained result from the maximum permissible for a certain climatic zone – 3.28 – 0.96 = 2.32.

The necessary layer size is thus obtained by multiplying the insulation’s thermal conductivity coefficient by the thermal resistance value. For instance, sheet foam with a 0.037 thermal conductivity coefficient will have a thickness of -0.037 x 2.32 = 0.08 m.

Optimizing the performance of concrete in construction projects requires a thorough understanding of its thermal conductivity. The ability of a material to conduct heat is measured by its thermal conductivity, which influences how warm a building stays. Engineers and builders can design buildings that are more energy-efficient and occupant-friendly by understanding how concrete transfers heat.

The thermal conductivity of concrete is affected by a number of factors. One important factor is the concrete mix composition. Thermal conductivity can be affected by fly ash or slag additions, cement, water content, and aggregates. Because denser materials typically conduct heat more effectively, changes in mix proportions can cause noticeable shifts in the thermal behavior.

The amount of moisture in the concrete is another crucial element. Wetter concrete generally has a higher thermal conductivity because water conducts heat more efficiently than air. Temperature and humidity are two environmental factors that affect moisture levels, which over time affects thermal performance.

Concrete thermal conductivity can be measured in the field using heat flow meters or in a lab setting using techniques like the guarded hot plate method. While each approach has pros and cons of its own, they are all geared toward producing reliable data for evaluating thermal performance. Engineers can more accurately forecast the behavior of concrete structures in a variety of climates and conditions by taking precise measurements.

More energy-efficient building materials and systems can be developed by taking thermal conductivity into account during the design phase. By choosing the right concrete mixtures and taking the environment into account, we can build structures that not only adhere to safety and structural specifications but also help achieve sustainability and energy-saving objectives. The capacity to precisely control the thermal characteristics of concrete will be crucial for creating the robust, energy-efficient buildings of the future as material science advances.

Video on the topic

Thermal conductivity of a flat wall

Lecture 1 Determining thermal resistance of enclosing structures

Lecture 4. Heat engineering calculation of enclosing structures

Intuitive understanding of the thermal conductivity formula (part 11) | Thermodynamics | Physics

Thermal conductivity coefficient.