When concrete is heated, the moisture inside the concrete converts to steam and expands, creating internal pressure and causing a section of concrete to break off. This process is called _____.

The process described in the question is known as spalling. When concrete is subjected to high temperatures, such as during a fire, the moisture trapped within it heats up and turns into steam. This steam expands and can create significant internal pressure within the concrete. If the pressure exceeds the tensile strength of the concrete, it results in pieces breaking off or flaking away from the surface. This phenomenon is specifically referred to as spalling.

Spalling is a critical concern in firefighting and construction because it can compromise the structural integrity of concrete elements in a building. Unlike other terms such as cracking, which generally refers to the formation of cracks due to stress, or chipping, which may imply a minor loss or damage to the surface, spalling indicates a more severe failure due to internal pressures caused by moisture expansion. Popping, on the other hand, can refer to the sudden release of energy in a more general context and does not specifically apply to the internal pressure created by steam within concrete. Understanding spalling is essential for firefighters when assessing the safety of structures after exposure to fire conditions.