Final answer:
Failure due to fire in lightweight concrete can occur because of reduced compressive strength under high temperatures and spalling from the rapid evaporation of moisture. This can lead to compromised structural integrity and eventual collapse of the structure if exposed to intense and prolonged heat.
Step-by-step explanation:
Failure due to fire in lightweight concrete can occur because it is less dense than traditional concrete, which can make it less structurally resilient in high heat scenarios. Lightweight concrete is composed of lightweight coarse aggregates such as shale, clay, or slate, and while it provides benefits like thermal insulation and reduced structural load, it can be compromised by fire at a faster rate than heavier, denser concrete.
Structures made with lightweight concrete can fail when exposed to prolonged high temperatures, which cause a reduction in the concrete's compressive strength and can lead to a loss in its structural integrity.
Additionally, the presence of moisture in lightweight concrete can lead to spalling when exposed to fire. This is a condition where the surface layers of concrete explode or peel away due to the rapid evaporation of moisture under intense heat.
It is also important to consider that lightweight concrete may have different fire resistance ratings, and structures should be designed in compliance with building codes that minimize the risk of fire-related failures.