Heat Resistant Concrete
When concrete is exposed to temperatures above 100 C, the boiling point of water, the moisture in the concrete can turn to steam. If the temperature rises more rapidly than the steam can escape through the concrete matrix, the rising pressure exceeds the strength of the concrete and it begins to spall. This spalling and be explosive in extreme cases.The effects of fire on concrete are greatly influenced by the type of aggregate used. Concrete containing carbonate aggregate (limestone) and lightweight aggregate (either naturally occurring or manufactured by expanding shale, clay, or slag) retain most of their compressive strength up to 650C. However, concrete containing siliceous aggregates, such as granite, quartzite and other materials consisting largely of silica, retain only about 55% of their compressive strength at 650C.
The damage to concrete caused by fire can range from minor cosmetic blemishes to more serious damage such as external cracking and spalling.
The most important factor to consider is the selection of aggregate. The differential thermal movement between the cement paste and the aggregate is what can cause damage. Quartzite aggregate is the most prone to fire damage and bond failure. Limestone aggregate exhibits better fire resistance when exposed to low-temperature fire.
At higher temperature ( above about 400 C), heat resistant concrete is generally needed. When temperatures get extremely high, (above 550C), calcium aluminate cement needs to be used.
However, it has recently been discovered that adding the unique new cement modifying product concrecem when producing concrete or mortar will produce an incredible increase in heat resistance. Cement mortars have subjected to temperatures of 2000C without any serious damage.
Properties Of heat resistant concrete
Usually, refractory cocnrete exhibit cracks after, first firing. These cracks are due to dehydration shrinkage and ceramic reaction between the cement and aggregate at high temperatures. In normal service conditions, these cracks will close down when concrete is reheated to its service temperature due to thermal expansion.
Application of Heat Resistant concrete
It is commonly used in runway pavements. Concrete pavement exposed to high temperatures from an aircraft is wet when the heat is suddenly applied, the production pavement of steam within the concrete can cause spalling, Typical concrete pavement damage resulting from the high temperature of jet blast includes sampling, aggregate popouts, scaling, cracking, and loss of joint sealant. The time that the concrete is exposed to the jet engine or auxiliary power unit exhaust is critical, Since there is a considerable thermal lag in concrete, properly designed pavements generally do not suffer heat damage from aircraft.
Advantages Of heat resistant Concrete
- Shrinkage:- The Refractory concrete does not warp during drying and firing, as they will set with a chemical reaction, Which is subsequently sintered to create ceramic bonds.
- Green strength:- The refractory concrete has a similar strength to convertible concrete even before it has been fired, it can be maneuvered far more easily than large fragile clay pieces.
- Fired strength and Toughness:- Once fired, refractory concrete is substantially harder than conventional due to the aggregate's ability to arrest crack propagation.