Concrete has good fire resistance and concrete structures generally perform well when fire damage occurs. However, the visual appearance of concrete after a fire can be quite shocking with extensive blackening often accompanied by spalling and cracking. Of more importance, though, is the depth and extent of the fire damage.
An assessment can be divided into four stages:
- Preliminary inspection
- On-site assessment of damage (by visual inspection, breakouts, coring and/or non-destructive testing)
- Laboratory testing of concrete and reinforcement samples to determine their residual strengths and confirm the depth of fire damage
- Repair options
Repair is usually possible but the key to assessing the type and extent of the required repairs is an accurate assessment of the damage caused by the fire. An important part of this assessment is evaluating temperature profiles and residual strength of the concrete.
Sandberg Services include:-
- Visual inspection and hammer soundings
- Non-destructive testing (including rebound hammer, ultrasonic pulse velocity, UPV)
- Sampling (coring drilling) and subsequent laboratory testing (including petrographic examination)
- Strength testing of concrete and reinforcement samples
Of these techniques, petrographic examination is central to estimating the depth to which the concrete has been damaged. Concrete exposed to fire undergoes a progressive series of mineralogical changes that can be investigated by petrographic examination. The appearance of a pink/red discolouration which coincides approximately with the onset of significant loss of strength due to heating is one of several changes which can be seen. The maximum temperature attained and the temperature profile can be assessed.
