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Improvements in building materials are constantly being made. The construction industry relies on wide concrete varieties for its many varied projects. Various constructions use refractory concrete to withstand high temperatures. Normal concrete melts at a particular temperature. High-alumina cement is often used to make refractory concrete, which can withstand high temperatures, along with aggregates that can also withstand heat.
Fig: Refractory Concrete
What is Refractory Concrete?
Refractory concrete is concrete that can handle high temperatures and doesn’t melt. Refractory concrete is also called heat-resistant concrete. High alumina cement or calcium aluminate cement is the most important ingredient for refractory concrete.
When high-alumina concrete is exposed to high temperatures, it will stretch slightly but still be strong enough to hold the normal load. Most of the time, crushed aggregate with alumina concrete is used to make refractory concrete. This material can handle temperatures as high as 1400 degrees Celsius. When temperatures are higher than about 400°C, heat-resistant concrete is often needed. Calcium aluminate concrete should be used when temperatures are extremely high (above 550°C).
But it was just recently found that adding a new kind of cement can change the concrete. Making cement or mortar will increase the ability to keep heat out unimaginably. Even when concrete mortars were heated to 2000°C, there was no real damage. Chimneys in buildings are made with refractory concrete because chimneys are exposed to high temperatures and need to be made with fire-resistant concrete.
Features of Refractory Concrete:
Ingredients Used to Make Refractory Concrete?
i) Refractory aggregate (Crush sand from the river)
ii) Refractory cement (Calcium aluminate cement)
Installation of Refractory Concrete:
i) Arrangement and Compaction of Refractory Concrete:
Installing and compacting heat-resistant and refractory concrete is crucial. Like conventional concrete, heat-resistant and refractory concrete is laid and cured without special tools or abilities. When using precast elements, measurements must be considered for formworks. If the area is inaccessible and cannot be cast properly, gunning is used by professional contractors.
ii) Curing of Refractory Concrete:
Curing concrete aims to keep it moist and maintain the hydration reaction, so it gains strength. Insufficient curing generates dusty, brittle concrete surfaces and failure under service loads. So curing calcium aluminum cement concrete is necessary. Curing heat-resistant and refractory concrete is comparable to ordinary concrete. However, curing calcium aluminum cement concrete must begin within 3-4 hours of placing due to quick hardening and high heat evolution.
iii) Drying and Firing of Refractory Concrete:
After curing, concrete will have much free water. If free water isn’t removed, fire-exposed concrete will spill. Before concrete is fired, removing as much free water as possible is advised by driven drying out at 100oC or natural drying. Hydration cement water is eliminated if the degree of heating exceeds 100oC up to 350oC. The plane of heat application depends on factors such as thickness, concrete type, and the project’s purpose.
A typical concrete heating plane heats concrete for six hours at 50oC to 500oC, then increases it to service temperature. When the concrete thickness is more than 500mm, it isn’t easy to dry it properly. So, make sure water vapor can escape. Adding organic fibers or porous aggregate to concrete can do this. In some cases, such as winter storage, heating is not allowed unless the concrete is fully wet.
iv) Reinforcement in Refractory Concrete:
If steel bars are put into refractory concrete and the concrete is exposed to high temperatures, the reinforcement must be done with care. High temperatures weaken the bond between steel and concrete, which can melt at very high temperatures and cause concrete to crack and change the way steel works. At 300oC, the bond between concrete and steel starts to weaken, and if the temperature goes up, the concrete starts to break up and crack. At higher temperatures, steel reinforcement can lose its purpose, and the presence of steel in concrete will no longer be beneficial.
v) Shrinkage and Thermal Expansion Refractory Concrete:
As you know, greater temperatures cause most substances to expand. The pore’s water molecules will evaporate as it heats. As a result, the concrete begins to shrink. When this happens, cracks occur. When the cracks are particularly deep, debris from the outside world can begin to make its way into the concrete, exacerbating the situation.
vi) Strength of Refractory Concrete after Firing:
When concrete is heated to almost 600°C, the hydraulic bond starts to break down. It makes the compressive strength of concrete go down. A ceramic bond begins to form when the temperature exceeds 600 degrees Celsius. When the cement and aggregate come together, a ceramic bond is made. Concrete is at its strongest point, but as it cools, it loses strength.
Types of Refractory Concrete:
1. High-Grade Refractory Concrete:
High-grade refractory concrete can stand up to high temperatures o,r it can stand up to high temperatures against hot faces. Instruments with hot faces can be made of concrete that doesn’t melt when it gets hot. Hot-face instruments are made of any material immediately attacked by warm origin.
2. Low-Grade Refractory Concrete:
This type of concrete can handle low heat levels. It can be used for low-temperature resistance.
Uses of Refractory Concrete:
Advantages of Refractory Concrete:
Disadvantages of Refractory Concrete:
Refractory concrete is a unique material that can keep its mechanical properties even after being exposed to high temperatures for a long time. High alumina or calcium-aluminate is used to make refractory concrete resistant to heat. Usually used in places with a lot of heat, like furnaces, fireplaces, and wood stoves.
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www.glasstechrefractory.com/blog-71/refractory-concrete. Accessed 4 Dec. 2022.
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