Understanding the effects of different heating rates on wet concrete structures is of primary importance to engineers and industry. This is because rapid heating of wet concrete and refractory materials can result in serious problems, in the event of explosive spalling. In that case projectiles of reasonable mass (1-10 kg) can be thrust violently over many metres. While surface spalling is less violent the extent of damage can still be severe and in both cases repairs will be required resulting in significant costs to industry.

There are two drivers for spalling of refractory concrete – thermal strain caused by rapid heating and internal pressures due to the vaporization of water. Thus being able to predict the outcome of different heating rates on thermal stresses and internal pressure during water removal is particularly important to industry using refractory and other concrete structures.

The current approach to drying and heating of refractory concrete following manufacturer’s procedures, can be long, conservative, and very costly. It is also known that even following very conservative heating schedules, explosive spalling of refractory concrete can still occurs.

Our work has found:

Many heating schedules are unreliable and don’t always prevent explosive spalling.
Increasing the heating rate can increase the maximum pore vapour pressure.
The use of thermal hold periods during drying does no aid nor prevent spalling if the hold period is not within the pressure peak zone.
Explosive spalling starts when the peak pore vapour pressure initiates a crack and the sudden release of the pressurized liquid water into steam that acts as the propellant.