Heat Resistant Concrete Installation and Applications

Heat resistant concrete, also known as refractory concrete, possesses exceptional capabilities to withstand and endure high temperatures. In the subsequent sections, we will discuss the installation and applications of this specialized type of concrete. Furthermore, we will explore the procedures for placing and curing heat resistant refractory concrete, as well as its various practical uses.

Fig.1: Heat Resistant Concrete or Refractory Concrete

Heat Resistant Concrete Installation and Applications

Heat resistant refractory concrete, also known as heat resisting concrete, requires proper placement and compaction techniques to ensure its integrity. During the placement process, it is important to carefully position the concrete mixture in the desired location and compact it thoroughly to eliminate voids and achieve maximum density.

Curing plays a crucial role in the development of heat resistant concrete. After placement, the concrete should be adequately cured to promote hydration and strength gain. This typically involves providing a moist and controlled environment to facilitate the curing process and enhance the concrete’s durability.

The drying and firing of heat resistant refractory concrete are essential steps to enhance its heat resistance properties. Once the concrete has cured sufficiently, it needs to undergo a controlled drying process to remove excess moisture. Subsequently, the concrete is subjected to high temperatures through firing, which further enhances its ability to withstand heat.

Reinforcement is often employed in heat resisting concrete to enhance its structural integrity. Steel reinforcement bars or fibers may be incorporated into the concrete mixture to provide added strength and improve its resistance to thermal stress and cracking.

Shrinkage and thermal expansion are important considerations when dealing with heat resistant concrete. Like conventional concrete, heat resistant concrete also experiences some degree of shrinkage during curing. Additionally, it exhibits thermal expansion when subjected to elevated temperatures. These factors need to be carefully addressed to prevent potential cracking or structural issues.

The strength of heat resistant concrete after firing is a critical parameter for its performance. The firing process contributes to the development of the concrete’s final strength, which is essential for its ability to withstand high temperatures and thermal cycling without significant structural deterioration.

Heat resisting refractory concrete finds applications in various industries. It is commonly used in furnace linings, kilns, and other high-temperature environments where thermal insulation and resistance to heat are required. The concrete’s ability to withstand extreme temperatures and provide structural stability makes it suitable for applications in the metallurgical, petrochemical, and power generation sectors, among others. Following is one by one explanation.

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Heat Resisting Concrete Placement and Compaction

The placement and compaction of heat resistant and refractory concrete are important processes. They are similar to ordinary concrete in terms of placement and curing, requiring no specialized tools or skills. Standard formwork materials are used, and careful consideration is given to dimensions when using precast elements. However, if the location is difficult to access or cannot be casted conventionally, gunning application may be considered. Skilled contractors perform this application method.

Heat Resisting Concrete Curing

Concrete curing is essential to maintain moisture and promote the ongoing hydration reaction, which allows concrete to achieve the desired strength. Inadequate curing can result in a dusty and weak concrete surface, as well as potential failure under normal usage. Therefore, proper curing is particularly crucial for calcium aluminum cement (CAC) based concrete. The curing process for heat resistant concrete and refractory concrete follows similar principles as conventional concrete. However, it is important to initiate the curing of CAC-based concrete within 3-4 hours after placement due to its rapid hardening and significant heat generation.

Heat Resistant Concrete Drying and Firing

After concrete curing is complete, excess water remains within the concrete. To prevent concrete spalling during fire exposure, it is necessary to remove this free water. Prior to subjecting concrete to fire, it is recommended to eliminate as much free water as possible through methods such as driven drying at 100°C or natural drying. If the temperature rises beyond 100°C up to 350°C, the water from cement hydration is expelled. The careful application of heat is crucial, and the specific heating plane depends on factors like concrete thickness, type, and project requirements.

A common approach involves heating the concrete for a minimum of six hours at a temperature of 50°C, gradually increasing it up to 500°C before reaching the desired service temperature. In cases where proper concrete drying is challenging, especially for thicknesses exceeding 500mm, it is advisable to create pathways for water vapor release. This can be achieved by increasing concrete porosity using organic fibers or porous aggregates. However, in certain circumstances, such as external storage during the winter period, heating should not be applied unless the concrete is allowed to become fully saturated.

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Reinforcement in Heat Resistant Concrete

When using heat-resistant refractory concrete with embedded steel bars exposed to high temperatures, careful attention must be given to the application of reinforcement. The elevated temperature can weaken the bond between steel and concrete, leading to potential melting at extreme temperatures and causing concrete spalling. This, in turn, can affect the properties of the steel. It is important to note that the bond between concrete and steel decreases at temperatures of 300°C, and further increases in temperature can result in concrete spalling and crack development.

At higher temperatures, the steel reinforcement may lose its effectiveness, rendering its presence in the concrete ineffective. To address this issue, it is recommended to place the steel reinforcement away from the heated surface of the concrete and avoid subjecting the steel to temperatures exceeding 300°C. In certain cases, special reinforcements such as mild steel and steel fibers can be used, particularly in heavily industrial areas, as they have the ability to withstand higher temperatures compared to regular steel.

Heat Resistant Refractory Concrete Shrinkage and Thermal Expansion

Cracks often form in heat-resistant refractory concrete when exposed to fire due to water loss-induced shrinkage. These cracks are likely to close over time and typically do not pose problems, as long as waste materials are prevented from entering them. However, if waste materials enter the cracks and the concrete is subsequently heated again, the cracks may widen.

Strength of Heat Resistant Refractory Concrete After Firing

Ordinary castables, containing approximately 15-25% cement by weight, start to harden within 3-4 hours of being placed, and they reach their highest strength after one day. When concrete is heated, its strength development is influenced by the presence of combined and free water. As the temperature rises further, changes in strength are primarily due to the reaction between calcium aluminum cement and the aggregate.

At around 500°C, the hydraulic bond in castable concrete decreases, resulting in a decrease in its strength. Once the heating surpasses 500°C, a ceramic bond forms between the aggregate and cement, depending on the type of cement and aggregate used. At this stage, the concrete exhibits increased strength as it cools but shows decreased strength when tested before cooling.

Low cement castables concrete displays increased strength both when exposed to high temperatures and during the cooling process. This type of cement performs exceptionally well in high-temperature conditions.

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Applications of Heat Resistant Concrete or Refractory Concrete

Heat resistant concrete, also known as refractory concrete, finds application in various scenarios such as fire training areas. These training areas encompass diverse features like wide flat surfaces, full-scale rooms or two-story buildings, fire staircases, and other structures used for fire training purposes. Additionally, heat resistant concrete is utilized in foundry floors, domestic flues, fireplaces, and chimneys. In fire training areas, not only is the concrete exposed to high temperatures, but it may also be subjected to the corrosive effects of chemicals generated from burning materials used to simulate fires. These chemicals can attack the concrete within the training area.

Foundry floors are exposed to continuous heating, thermal shocks, abrasion, and impacts. To ensure their durability, concrete capable of withstanding high temperatures, impacts, and abrasion needs to be used. One suitable option is a combination of calcium aluminum cement concrete and a synthetic calcium aluminate aggregate.

Chimneys are exposed to heat and potential chemical damage from acid present in flue gases.

FAQs about Heat Resistant Concrete