Refractory cement – main characteristics

A unique kind of cement known as refractory cement is capable of withstanding very high temperatures. Refractory cement is made to withstand temperatures that would otherwise dissolve ordinary materials, unlike regular cement, which can weaken and crack in extreme heat. Because of this, it is a crucial part of many applications and industries where high heat is a factor.

Refractory cement’s resistance to heat shock is one of its main qualities. Rapid temperature changes can cause materials to expand and contract, which can result in cracks and structural failure. This phenomenon is known as thermal shock. Refractory cement is perfect for use in furnaces, kilns, and fireplaces because it is designed to withstand these stresses without degrading.

The durability of refractory cement is another crucial aspect. It offers enduring performance in demanding settings because it can withstand extended exposure to high temperatures and harsh environments. This durability lowers maintenance costs and repair downtime in addition to increasing safety.

Refractory cement is also known for its excellent insulating properties. It helps to retain heat within furnaces and other high-temperature equipment, improving energy efficiency and reducing fuel consumption. This makes it a cost-effective and environmentally friendly choice for many industrial processes.

For anyone working in the construction industry or any other industry that uses materials resistant to heat, it is essential to comprehend the primary features of refractory cement. For high-temperature applications, the proper kind of cement can be chosen to guarantee the longevity, effectiveness, and safety of your projects.

A unique kind of cement called refractory cement is made to withstand high temperatures without disintegrating. Its outstanding heat resistance, robustness, and capacity to preserve structural integrity in adverse circumstances are some of its primary qualities. Refractory cement is perfect for use in furnaces, kilns, and fireplaces because it guarantees long-lasting performance in conditions where regular cement would break down.

Where refractory cement is used

Refractory cement made of aluminous material can withstand high outside temperatures. This kind of binder maintains its characteristics at 1,750–1,800 °C, which is about the same as the melting point of steel.

By way of comparison, structures built using Portland cement for general construction start to collapse at 250 °C, and the damage becomes irreversible at 500 °C and elevation.

What refractory cement is used for:

• Preparation of masonry mortars for the construction of heating stoves and fireplaces.
• Preparation of solutions for capturing furnaces and fireplaces of furnaces.
• Preparation of solutions for the construction and operation of industrial (tunnel, muffle, laboratory, etc.) furnaces.
• Industrial production of refractories, mortars, dry refractory mixtures, general-purpose concrete monoliths.

According to its technical definition, "refractory" cement is a binder with a unique composition that sets and hardens through the creation of "ceramic bonds." In this instance, "hydraulic bonds" form as the general construction cement hardens and sets.

Characteristics of refractory cement

The process of joint sintering and extremely fine grinding multiple components yields aluminous cement. Refractory cement’s composition specifically consists of the following elements:

• Refractory alumina not less than 60%. Main component.
• Calcium oxide up to 35-40%.
• Additives up to 3-5% no more.

Externally and tactilely, commercial heat-resistant cement is a finely dispersed (depending on the alumina content) powder of dark brown, gray, light gray, or whitish color when sifted laboratory samples through a test sieve with a cell size of 0.08×0.08 mm, the permissible "no more than 10%"

Features of the refractory cement-based concrete mixture:

• Compressive strength: 250-600 kgf / cm2 after 24-72 hours after mixing the composition.
• Resistance to harmful factors (acid, alkali, mineral hydrocarbonate water, sulfates, etc.): high.
• Structure of the hardened material: low-porosity, impermeable to moisture.
• High level of heat release generated during cement hydration: up to 70% in the first 24 hours after mixing from 100%.
• Permissible operating temperature of products and structures: 1,200-1,800 °C depending on the type and amount of additives (chamotte powder, chromium powder, magnesite powder).

Marking of heat-resistant cement

Document GOST 969-91 regulating. Heat-resistant cement can be classified into the following types based on the amount of aluminum oxide (Al2O3) in the binder: "Aluminous and high-alumina cements"

• Aluminous material GC.
• High alumina material VGC I, VGC II, VGC III.

The following grades of cement are distinguished by GOST 969-91 based on the concrete strength attained in 72 hours:

• GC 40, GC 50, GC60.
• VGC I-35.
• VGC II-25, VGC- 35.
• VGC III-25.
• VGC 70-VGC 75
• VGC-70-1.

Arabic numerals 40, 50, 60, 25 and 35 tell the customer that, 72 hours after mixing and under standard strength gain conditions (air temperature 20–25 °C, relative humidity 75–80%), concrete material based on a specific type of refractory cement will have a compressive strength of 40 MPa, 50 MPa, 60 MPa, etc.

An illustration of a heat-resistant cement designation is: GOST 969-91, Refractory Cement GC 40. Refractory cement with alumina. Attainable compressive strength of 40 MPa, or 400 kgf/cm2, after 72 hours of mixing the concrete mixture. 780–1,000°C is the empirical refractoriness. GOST 969-91 does not regulate this type of binder’s refractoriness.

Purpose of certain types of heat-resistant cement

• Aluminous cement GC40-GC60. Production of dry refractory mixtures, road construction, concreting at sub-zero temperatures, coating of domestic furnaces and fireplaces.
• High-alumina cement VGC 70-VGC 75, VGC I-VGC III. Construction of structures operating at very high ambient temperatures. Production of fast-hardening concrete mortars for various purposes.
• High-alumina cement VGC-70-1. Production of refractories, lining of industrial furnaces, construction of furnace substrates.

Prices for refractory cement

Refractory cements are relatively expensive due to their unique manufacturing technology and purpose. Furthermore, this kind of material is typically made in large batches upon request. Refractory cement currently costs the following at retail:

• Cement GC-40, GC-50, GC-60: 1,600 rubles per bag weighing 50 kg. Manufacturer OJSC Pashiyskiy Metallurgical-Cement Plant, Russian Federation.
• Cement VGTs 70-VGTs 75, VGTsI-VGTsIII: 1480-1550 rubles per 20 kg bag. Manufacturer OOO NTZGTS (NIZHNETAGIL ALUMINA CEMENT PLANT), Russian Federation.
• Cement VGTs-70-1: 1,580-1,680 rubles per 20 kg bag. Manufacturer OOO Konsolit, Russian Federation.

How to make refractory cement with your own hands?

The extremely high cost and restricted supply of specialty refractory cement pose challenges for regular private developers who wish to have access to heating fireplaces and stoves.

Online resources abound regarding the preparation of refractory cement for stoves and fireplaces using a variety of heat-resistant additives, such as expanded clay, asbestos (which is toxic), blast furnace slag, broken fireclay bricks, fly ash, and even chromite ore, which is available for purchase.

We can draw conclusions from the real-world experience of a heating stove operating successfully in a private home. The construction and functioning of the firebox and other stove structures beneath the building’s roof may require the use of a 1:1 mixture of clay and sand, along with a sealer with a consistency similar to "homemade sour cream."

You can use a solution prepared in accordance with the above proportion for the construction of a chimney and a portion of the chimney situated beneath the building’s roof. The portion of the chimney that is situated above the building’s roof is constructed using masonry mortar that is made in accordance with a recipe that calls for mixing regular Portland cement, regardless of brand, with sand in a 1:2 ratio.

Conclusion

It is acceptable to build private heating structures using aluminous cement that is heat-resistant. When considering the costs associated with the construction and ongoing maintenance of private buildings, this is not economically justified.

Specialized material made to withstand extremely high temperatures is called refractory cement. Due to its special qualities, it is indispensable in heat-sensitive industries like glass and steel manufacturing. Structures exposed to intense heat are guaranteed to last a long time and to be safe because of the cement’s ability to hold its integrity in these circumstances.

Refractory cement’s high heat resistance is one of its main qualities. Because of this, it functions well in conditions where ordinary cement would not. Building furnaces, kilns, and other high-temperature facilities is a dependable option due to its strength and resilience to thermal stress.

The resistance of refractory cement to thermal shock is another crucial feature. This indicates that it won’t break or degrade when exposed to sudden temperature changes. This characteristic is essential for preserving the stability of buildings that experience repeated cycles of heating and cooling.

Refractory cement, in conclusion, is an essential component for any application involving high heat. In high-temperature industries, its durability, thermal resistance, and capacity to tolerate thermal shock render it indispensable. Heat-exposed structures are guaranteed to be safe, effective, and long-lasting when refractory cement is used.

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