What is created when water in concrete turns to steam during a fire?

When water in concrete is subjected to high temperatures during a fire, it can turn to steam. This rapid conversion causes an increase in pressure within the concrete, leading to a phenomenon known as spalling. Spalling is the process where layers of the concrete surface break away, chip off, or explode outward. This occurs due to the high vapor pressure generated by the steam, which can cause significant structural damage to the concrete.

The formation of spalling is critical to understand since it can weaken the structural integrity of concrete elements in a building during a fire. This not only endangers the structure but also poses serious risks to firefighters and occupants due to the potential for falling concrete debris.

In contrast, the other terms have different meanings; char refers to the blackened, carbonized material produced from the thermal degradation of organic materials during combustion. Calcination is the thermal decomposition of materials at elevated temperatures, often referring to the chemical transformation of minerals. Oxidation is a chemical reaction where a substance combines with oxygen, and while it can occur in various materials during a fire, it does not specifically pertain to the water in concrete turning to steam. Understanding spalling's role in fire dynamics is essential for effective fire investigation and safety considerations.