I am investigating on the effect of a fire that gutted a concrete building. I am determining the residual strengths of the structural and building elements after the fire. Is there a way of estimating the maximum temperature that was reached during the inferno?
By the change of color, crack width and patterns , NDT, checking with standard chart for the compressive compressive strength change if you know the early strength,if not again it should be find out by doing NDT on unburnt building place.
You can see the physical properties and chemical changes in the concrete
300°C will lead to cracks due to the shrinkage of cementstone and the expansion of the aggregates, at 700°C limestone will be changed to CAO, 1100°C cementstone will start to melt like glass.
Change of pH is also one of the method, but not proven fully, or accepted fully,
Best method is to take cores of intact building concrete of same building and burnt place cores, check its compressive strength, it's always known for the approximate amount of time building under fire. If not approximate time is enough. Take pictures of various places for change of color.
Put cores in furnace at different temperatures for the time equal to the exposure,
Check colors change and strength at every temperature interval. Keep an eye on the similar Color or/ and in which the residual strength of core is equal or nearly equal to the core strength of burnt concrete building. That temperature is the temperature it raised.
During a fire, the temperature reaches 1000 ° C in Materials surface.
Concrete is a material Who Owns a good behavior when it is Subjected to high temperatures, it present inertia to the propagation of heat flow in its mass, and the temperature rises Slowly.
- Around 500 ° C: dehydration portlandite (Ca (OH) 2)
- Around 575 ° C: transformation of quartz "a" quartz "b"
- Between 700 ° C and 900 ° C: decarbonisation carbonate (CaCO3)
- From 1200 ° C and 1300 ° C TO: Start fusion of compounds Silicates concrete.
- After 1300 ° C: the concrete is in the melt.
1. By visualizing the change in colour.
2. A comparative assessment of unaffected and affected parts by a suitable NDT such as rebound hammer or a UPV instrument.
3. Finally, employing XRD and TGA investigations.
http://keu92.org/uploads/Search%20engineering/STRUCTURAL%20APPRAISAL%20FOR%20FIRE.pdf
I hope this reference will help you... :
STRUCTURAL APPRAISAL FOR FIRE DAMAGED BUILDINGS BY Dr. Rizgar Salih Amin (BSc,MSc,PhD)