Heat-resistant concrete: characteristics, application

One particular kind of concrete made to resist high temperatures is called heat-resistant concrete. Heat-resistant concrete retains its structural integrity in high temperatures, which makes it perfect for a variety of high-temperature applications. Regular concrete, on the other hand, can weaken or crack in extremely hot conditions. Its special quality makes a variety of applications in construction projects possible where temperature resistance is essential.

Heat-resistant concrete’s capacity to withstand temperatures far higher than those that regular concrete can handle is one of its primary qualities. Its thermal properties are improved by the application of particular materials and additives. Consequently, heat-resistant concrete finds widespread application in industrial environments like kilns, furnaces, and chimneys, where it is essential for preserving longevity and safety.

Heat-resistant concrete has uses in both commercial and residential projects in addition to its industrial uses. It can be utilized, for example, to build outdoor ovens, barbecues, and fireplaces. Its capacity to withstand heat makes it a dependable option for these projects, guaranteeing enduring performance even in the most demanding circumstances.

All things considered, heat-resistant concrete is a crucial component of many building projects that demand extraordinary toughness in high temperatures. Its distinct qualities

General information, materials and characteristics of heat-resistant concrete

The following categories of heat-resistant concrete are distinguished from heat-resistant products based on their structural makeup and functional purpose: structural and heat-insulating.

Composition of dense fire-resistant solutions

Dense heavy heat-resistant concretes are used to make building structures that can withstand fires as well as serving as a heat-resistant lining in thermal units such as blast furnace recuperators, chemical industry facilities, brick-firing kilns, chimney construction, etc. In addition to lowering costs and labor intensity, the use of heavy heat-resistant solutions can shorten the time needed for thermal unit construction and repair.

Binders

Heat-resistant concrete can be made on the following types of binders, per GOST 20910 90, while taking the specifications of the document and the operational conditions of the structures into consideration.

1. Portland cement with the presence of finely ground additives (microfiller).
2. Slag Portland cement with microfillers.
3. Aluminous and high-alumina cement.
4. On liquid glass.

It is advised to use concrete on slag Portland cement and Portland cement in alkaline and neutral environments; mixtures on liquid glass in acidic gas environments; solutions on aluminous and high-alumina cements in carbon, phosphorus, and hydrogen environments.

Mineral components are added to the astringent (the battle of magnesite or chamotis bricks, under-and-aids, domain granular slag, loom-shaped loam, Cinderella, etc.), which have the required fire resistance indicators, in order to improve the structure of the cement composition and increase the strength of structures.

Fillers

Destructive processes in the fillers and cement binders occur when reinforced concrete structures are heated. The uneven thermal expansion of mineral fillers explains the occurrence of these reactions. As a result, when selecting aggregates for a particular brand of heat-resistant concrete, you must proceed cautiously.

It is possible to use conventional aggregates at temperatures up to 200°C. Strength characteristics are seen to decrease as temperature rises above this minimum. Furthermore, conventional aggregates disintegrate at 600°C and above.

In addition to not softening or collapsing after extended exposure to high temperatures, fillers for heat-resistant concrete shouldn’t cause the structure’s internal stresses to increase as a result of heating.

The specified temperature conditions for each type of filler’s operation determine which one to use:

1. At a temperature mode from 600 ° C to 800 ° C, rocks (basalt, Andesitis, diabase) can be used as aggregates), granulated blast furnace slag, porous aggregates from volcanic rocks, broken bricks, porous artificial aggregates (expanded clay, vermiculite, expanded perlite, slag pumice, etc.).
2. For the operation of concrete structures within the range of 1200°C–1700°C, heat-resistant cement mortars are made with the addition of crushed refractory materials (magnesite, fireclay brick, chromite, burnt kaolin, corundum).
3. In addition, special fillers are used, made by high-temperature firing of a mixture of magnesite and refractory clay — magnesium aluminosilicates, characterized by low temperature deformation, high fire resistance in a wide temperature range.

Technical requirements for heat-resistant solutions

The following are the technological specifications for the primary categories of heat-resistant mixtures used in construction that are made using slag Portland cement, liquid glass Portland cement, or aluminate (alumina) cements:

1. The grade of concrete (according to GOST heat-resistant concrete) must include the following main characteristics: type of concrete (BR – heat-resistant); type of binders (P — on Portland cement, A — aluminate (alumina) cement, S — on silicate binders).
2. Concrete class by tensile-compressive strength (Bl B40).
3. Permissible temperature of material use (IZ I18).

As an illustration, the designation BR P B20 I12 for heat-resistant concrete on Portland cement of strength class B20 with an allowable usage temperature of 1200 °C will appear.

1. Products with an average density of 1100 kg / m3 and below are used as heat-insulating material for unloaded enclosing structures.
2. Products with a density of> 1400 kg / m3 are used for the construction of load-bearing enclosing structures of residential and public buildings.
3. According to the maximum temperature of use, concretes are divided into 18 classes. Heat-resistant classes I13–I18 are recommended for use only for non-load-bearing structures.

1. For concretes with an average density of 1500 kg/m3 and designated for the manufacture of concrete structures, the following water resistance standards are established: W8, W6, W4 and W
2. Concrete products of the same grades must have the following frost resistance: F75, F50, F35, F25 and F
3. Along with the above parameters, materials are classified by residual strength and deformation temperature under mechanical load. These indicators depend on the heating temperature and the type of binders in the material.
4. For heat-resistant products, the following strength classes are provided: B1–B For pre-stressed heat-resistant structures used in high-temperature conditions, the tensile-compressive strength class must be B30 and higher. For structures without load – more than B12.5.

Main types of heavy fire-resistant concrete

As was previously mentioned, different kinds of fire-resistant concrete are used depending on the materials and intended use of heat-resistant structures. Let’s take a look at a few of the most fundamental and widely used refractory material types.

Heat-resistant concrete on Portland cement and slag Portland cement

Slag concrete solutions The first and most popular class of heat-resistant concrete is Portland cement and Portland cement. They can successfully compete with other materials of a similar nature thanks to their relatively low cost, tested technologies for the production of industrial and building structures for thermal purposes, and reasonably high strength characteristics.

These kinds of heat-resistant concretes are used to build thermal units, chimneys, nuclear power plant fire-resistant structures, and other high-temperature-indicating structures.

Portland slag cement and Portland cement-based dense, heat-resistant mixtures must meet strength classes B15–B40.

Portland cement (grade 400 and above) is the basis for concrete, and only active mineral additives (blast furnace slag, fireclay, fuel ash, etc.) are used in its production. The addition of finely ground fireclay to concrete solutions’ composition yields the highest strength indicators.

Portland slag cement can be used safely to prepare concrete at temperatures not to exceed 700°C because it already contains blast furnace metallurgical slag.

Concrete based on alumina (aluminate) cement

Concretes of high heat resistance classes (I8–I18) are prepared on aluminate, high-alumina, and aluminous cements. The mineralogical makeup of aluminate cements explains their high fire resistance.

Calcium monoaluminate is the primary mineral found in aluminous cement (CaO Al2O3). Calcium dialuminate (CaO 2Al2O3) is used in high-alumina cements.

Without additional additives, heat-resistant concrete structures built on aluminate cements can tolerate temperatures as high as 1300°C. By adding fillers made of corundum and aluminum oxide, the temperature range can be raised to 1600°C and higher.

Principal attributes of goods made with aluminous cements:

1. High mechanical strength.
2. Stable state with sharp changes in the operating temperature regime.
3. Low thermal shrinkage.
4. Low linear expansion rate when heated.
5. Low thermal conductivity.

After just one day of production, fire-resistant structures made with aluminous cements can be exposed to high temperatures. The table below (see photo) provides the ideal compositions of heat-resistant concretes on aluminate cements.

Liquid glass as a binder for heat-resistant concretes

Refractory concretes with a maximum use temperature range of 800°C to 1600°C are made using liquid glass compositions containing sodium or potassium. The density of potassium liquid glass is 1.4–1.56 kg/cm3, while the density of sodium liquid glass is 1.36–1.45 kg/cm3.

• B — high-modulus;
• B — medium-modulus;
• A — low-modulus.

• The best indicators of potassium glass, as the main binder in the composition of concrete, are manifested with a silicate modulus equal to 2.5–4.0, and sodium binder — at 2.0–3.5.
• The hardening process of liquid glass in natural conditions is very slow. To accelerate the hardening of mixtures, hardeners are added to its composition: alkali metal fluorosilicate and sodium fluorosilicate compound.
• Interacting with liquid glass, hardeners reduce the content of alkaline reagents. They promote the release of silicic acid, with the help of which the concrete mixture is compacted and its strength characteristics are increased.
• To accelerate the hardening of liquid glass, metallurgical processing products can also be introduced – nepheline sludge, ferromanganese slag, ferrochrome, etc.

Concrete mixtures on liquid glass may also contain finely ground additives, plasticizers, fillers, and hardening process regulators in addition to hardeners. along with additional elements that enhance the final performance characteristics of completed structures and make concrete mortar easier to work with.

Between 250 and 400 kg of binder are used for every m3 of concrete mixture. The hardener’s volume, which typically represents 0.1–0.2 parts of the binder mass, is determined by the volume of liquid glass. Filler consumption: 0.12–0.3 parts per glass of liquid.

Since pouring the mixture into the structure shouldn’t take longer than 30 minutes, concrete solutions on liquid glass are typically prepared on site. When laying concrete outdoors, the ambient temperature should be at least 15°C and the relative humidity should not exceed 70%.

A specific type of building material called heat-resistant concrete is made to endure high temperatures without deteriorating. For use in industrial furnaces, fireplaces, and other locations subjected to high temperatures, this kind of concrete is perfect. Because of the materials in its special composition, such as binders and refractory aggregates, it can perform well and retain structural integrity under extreme heat conditions. This article examines the salient features of heat-resistant concrete, its range of uses, and the advantages it provides in industrial and construction contexts.

Lightweight porous and cellular heat-resistant concretes

The same binders (primarily Portland cement and aluminous cements) that are used to produce heavy concretes can also be used to produce porous and cellular lightweight concretes. Lightweight heat-resistant concretes are produced by using porous special fillers, and cellular concretes are produced by adding special foam or gas-forming agents to the composition of concrete mixtures.

Lightweight porous concretes

For these types of concretes, porous materials that can withstand temperatures between 700°C and 1000°C are used as fillers.

• expanded perlite;
• expanded clay;
• volcanic tuff;
• vermiculite.

The following grades are defined for lightweight concrete, taking into consideration the material’s average density: D300–D1800.

Lightweight porous concretes are categorized into the following classes based on how they are applied:

1. Thermal insulation. The density of the material should be 500 kg/m3 or lower, thermal conductivity maximum 0.14 W/m*K, strength M14–M25.
2. Structural and thermal insulation: density 500–800 kg/m3, thermal conductivity — 0.14–0.54 W/m*K, strength M35 or more.
3. Structural — the density should correspond to 1400–1800 kg/m3, strength M50 or more. Thermal conductivity for structural concretes is not standardized.

Lightweight concretes with Portland cement and aluminous cement have a high fire resistance, and the material’s frost resistance is greatly increased when expanded clay crushed stone is used as a filler (F25–100).

Cellular concrete

Because of their low thermal conductivity, lightweight cellular concretes are mostly used as heat-resistant materials and for thermal insulation in large-scale construction. They have a much higher fire resistance than traditional compositions.

Both autoclaved and non-autoclaved cellular concretes are commonly utilized in individual construction as well as as components of prefabricated concrete structures.

Lightweight cellular concretes are categorized into four groups based on their intended use:

• thermal insulation (up to 500 kg/m3);
• thermal insulation and structural (500–900 kg/m3);
• structural (1000–1400 kg/m3);
• heat-resistant (800–1200 kg/m3), with a use temperature of up to 800°C.

For three to seven hours, cellular concretes (also known as foam concrete or aerated concrete) can resist the effects of an open fire without causing visible structural damage. Conventionally manufactured aerated concrete products show an increase in strength when heated to 400 °C; however, the structure of the concrete completely collapses when the temperature reaches 1000 °C.

The following binders can be used to raise the fire resistance limit of cellular concrete structures if needed:

• lime-belite (800°C);
• fuel ash and metallurgical slag;
• alkaline aluminosilicate binders.

Application of heat-resistant concrete

Special fire-resistant structures are constructed using heat-resistant concrete primarily in industrial construction. Prefabricated products made at specialized businesses or concrete heat-resistant mixtures made at the location of refractory structure application are used for the construction of structures made of heat-resistant concrete.

Commissioning of new concrete structures happens after the heat-resistant concrete reaches its design strength; for products based on Portland cement, quick-hardening cement, and liquid glass, the commissioning period is at least 7 days, but not less than 3 days.

The dried hardened mixtures are used to eliminate free water from boiler structures and heat-resistant concrete units before heating them. Furthermore, the subsequent heating is done in accordance with specific modes outlined in the technological instructions for each unit, contingent upon the type of binders.

Production of fire-resistant concrete at home

Heat-resistant concrete is used in the construction of stoves, fireplaces, chimneys, and other structures that are subjected to high temperatures on a regular or occasional basis.

Therefore, after deciding to decorate your home with one of the above-listed designs, you might be wondering how to make heat-resistant concrete yourself. Using ready-made, dry, high-temperature resistant mixtures is the simplest and first method for creating fire-resistant mortars. These mixtures are widely available at hardware stores across cities.

Usually, the packaging of the product you bought contains preparation instructions for these types of concretes. Additionally, the idea itself is as follows: Using a concrete mixer, add the completed dry mix and mix for one minute. Next, blend the solution with diluted glass or regular water, depending on the future mixture’s composition.

The following procedures can be used to prepare heat-resistant concretes from separate components, and they are not very difficult to do:

1. The optimal composition of materials for the preparation of concrete mix on Portland cement, we check against the table "Approximate composition of concrete on Portland cement with mineral ligatures", placed above in the text of the article, in the chapter: "Heat-resistant concrete on Portland cement and slag Portland cement".
2. First, pour 90% of the required amount of water or diluted liquid glass into the concrete mixer.

1. Fill in the finely ground additive. Then add half of the total volume, filler and cement. Mix the loaded mixture thoroughly, and without turning off the concrete mixer, gradually load the remaining amount of filler, and add the rest of the water or liquid glass.

1. The mixing time of the mixture should not be less than 5 minutes.

Hints: It is advised to combine the hardener and finely ground additive first when creating a concrete heat-resistant solution on liquid glass.

1. The finished concrete mixture is unloaded from the concrete mixer and transported for laying in prepared forms or formwork.

Characteristics	Application
Resistant to high temperatures	Furnaces and fireplaces
Durable and strong	Industrial kilns
Low thermal expansion	Chemical plants
Good thermal insulation	Power plants
Can withstand thermal shocks	Boilers and chimneys

A useful option for building projects requiring materials able to withstand high temperatures is heat-resistant concrete. Because of its special makeup and characteristics, it works perfectly in places like industrial furnaces, chimneys, and other buildings that are subjected to extreme heat. Even in harsh environments, this kind of concrete retains its strength and stability thanks to the addition of particular aggregates and binders.

Heat-resistant concrete has uses outside of the industrial sector. It is also used in residential settings, especially in outdoor cooking areas and fireplaces, where traditional concrete may not hold up. Because of its resistance to thermal expansion and cracking, builders and homeowners alike can feel secure in its longevity and safety.

To sum up, heat-resistant concrete is a unique material that combines high performance and practicality. It provides dependable protection and longevity in high-temperature environments, making it suitable for both home and industrial projects. This type of concrete proves to be a crucial part of contemporary construction as the need for strong and heat-resistant building materials grows.

Video on the topic

Heat-resistant concrete! Barbecue – grill with a hood made of concrete. DIY assembly.

Testing heat-resistant concrete ALPHAPOL BR P at 800 ° C

Terracotta. Reinforced heat-resistant glue

Heat-resistant concrete from B-70, UHPC. Collection of ingredients from all corners of Ukraine and neighboring countries.