Fire Resistance

As the rate of increase in temperature in CRC is similar to that of conventional concrete, conventional calculation methods can be used in design for fire resistance. This means that if 60 minutes of fire resistance is needed for a structural component, the cover to the reinforcement is typically 15 to 20 mm depending on how the reinforcement is utilised. A number of full scale fire tests have been carried out with CRC.

As a high performance concrete there is a risk of spalling with CRC that also has to be taken into account. The low porosity, which is an asset with regard to durability, may in some cases represent a liability with regard to fire resistance, as the risk of spalling will typically increase in proportion to a decrease in the permeability of the concrete.

Research has shown that residual properties of CRC - properties determined one week after fire exposure - are better than for conventional concrete, also comparatively, due to the low content of Ca(OH)2 in CRC.

If very young CRC specimens are exposed to fire, the risk of spalling is greater than with conventional concrete. As the risk of spalling depends on the relation between moisture content and permeability, a way of reducing this risk is to reduce the moisture content of CRC. This can be achieved either by drying or by waiting for a few months as the cement content in CRC is very high and water/binder ratio is typically only 0.16. This means that the relative humidity inside a CRC cylinder stored in water for a year is lower than 60% due to self desiccation.

Article in Concrete Engineering International

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