Properties of hardened concrete
-Resistance of concrete to fire
Concrete offers great fire resistance to structures. It is reasonably physically stable to about a thousand degrees Fahrenheit, and even above that temperature it usually does not fail dramatically. Because of concrete’s inherent material properties, it can be used to minimize fire risk for the lowest initial cost while requiring the least in terms of ongoing maintenance. In most cases, concrete does not require any additional fire-protection because of its built-in resistance to fire. It is a non-combustible material (i.e. it does not burn), and has a slow rate of heat transfer. Concrete ensures that structural integrity remains, fire compartmentation is not compromised and shielding from heat can be relied upon.
-Frost resistance
Concrete may be damaged by expansion of ice crystals , which are most likely to form in capillary pores or cracks, resulting initially from mixing water which was surplus to that required to hydrate the cement. Air entrainment admixtures form discontinuous pores which improve resistance to frost.
-Permeability
Concrete which is made with a low water : cement ratio and is very thoroughly compacted has good resistance to the absorption of water. Admixtures can sometimes contribute to impermeability but no concrete is completely impervious to water vapour.
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