Mechanical properties of concrete at elevated temperature are determined by testing plain concrete
specimens using one of three types of steady-state temperature tests: stressed tests, unstressed tests, and
unstressed residual property tests. Briefly, in stressed tests, a preload (20 to 40% of the room temperature
compressive strength) is applied to the specimen prior to heating and is sustained during heating. Heat is
applied at a constant rate until a target temperature T is reached, and is maintained for a time t until a
thermal steady state is achieved. Stress or strain is then increased at a prescribed rate until the specimen
fails. In unstressed tests, the specimen is heated, without preload, at a constant rate to the target
temperature, which is maintained until a thermal steady state is achieved. Stress or strain is then applied
at a prescribed rate until failure occurs. In unstressed residual property tests, the specimen is heated without
preload at a prescribed rate to the target temperature, which is maintained until a thermal steady state is
achieved. The
specimen is then
allowed to cool, at a
prescribed rate, to
room temperature. The
specimen is tested at
room temperature.
These three types of
test are schematically
shown in