Concrete is a non homogenous material whose fire performance is controlled by that of the aggregate and the cement paste. Concretes are conventionally grouped as normal-weight concrete (NWC) and lightweight concrete (LWC), depending on the density of the aggregates used. There has been considerable interest recently in high-strength concrete (HSC) as a high performance construction material due to its superior strength (with compressive strength at least 50 MPa), stiffness and durability.

Concrete has a low thermal conductivity (50 times lower than steel) and therefore heats up very slowly in a fire. It is the low thermal conductivity that provides good inherent fire resistance of concrete structures. The main concern of using HSC is its higher susceptibility to explosive spalling during a fire attack.

Thermal and mechanical properties of different types of concrete at elevated temperatures are discussed. These include:

• normal-weight concrete
• lightweight concrete
• high-strength concrete

The performance of reinforcing and prestressing steels in fire will also be discussed.