Under the fire resistance of concrete a short-term reaction to fire is meant, while heat resistance of concrete is resistance to long-term and permanent high temperatures. Concrete is one of the not many solid fire resistant materials. Due to the relatively low thermal conductivity of concrete short-term exposure to high temperatures does not have time to cause significant heating of concrete and reinforcement covered with protective layers. This is where watering strongly heated concrete with cold water (primarily in fire fighting) is much more dangerous, as it inevitably causes the formation of cracks, the destruction of the protective layer and exposing the valve with continued high temperatures.
Under conditions of prolonged exposure to high temperatures conventional concrete based on Portland cement is not suitable for use at temperatures above 250°. It was found that when heated above 250-300° a reduction in the strength of the decomposition of calcium hydroxide and the destruction of the structure of cement stone. At temperatures above 550° grains of quartz sand and crushed granite start to crack due to the transition of quartz at these temperatures in another modification (tridymite), which is associated with a significant increase in the volume of quartz grains and the formation of microcracks at the point where the grain and cement stone are connected. At higher temperatures a range of other structural elements of conventional concrete is destroyed.
Heat-resistant concrete production for extreme t
However, there are ways to create heat-resistant concrete, resisting the temperatures of 1100-1200° or more. And according to scientific Telling Company experts, a UK-based engineering business, widely utilising hydraulic lime, lime mortar and concrete technologies, such technology will become the production standard in the nearest decade
To achieve this, the concrete grinding mill must have siliceous additives or binding free calcium hydroxide released during the hydration of cement. As the fillers materials having a sufficient degree of fire resistance and heat resistance are used, such as chromium iron ore, fire clay, basalt, andesite, depleted blast furnace slag, tuff and brick rubble. The maximum temperature such design can withstand depends on the fire resistance and thermal stability of aggregates and additives. Thus, the application of fire clay and additives increase the maximum operating temperature of fire-resistant concrete up to 1100-1200°. With a maximum operating temperature of 700° basalt, diabase, andesite, depleted blast furnace slag can be used as concrete fillers and as additives – pumice, fly ash and blast furnace slag can be utilised. For the same temperature (700°) it is permitted to replace Portland cement in concrete with slag Portland cement without introducing fine additives.
For the preparation of heat-resistant concrete with operational temperatures up to 1300-1400° aluminous cement should be used with small and large aggregates of grog or chromium iron ore. Mill ground additive for binding of calcium hydroxide in this case is not required. As a binder for heat-resistant concrete with a maximum temperature up to 900-1000° liquid glass with sodium silicofluoride can be used.