Wanted to get input/feedback on reusing a slab after the 2 story brick house burnt to the ground
Hyper-heated concrete and bolts being flash cooled with water could present some structural issues
Interior wall plans will not align with the old design
Obvious bearing issues need to be accounted for
Plumbing or other stub up issues…
I’ve rebuilt one slab and one PB and know what issues may be encountered
Looking forward to replies
Hi. Barry;
Found this in Wikipedia that explains fairly well what happens to concrete in a fire.
Due to its low thermal conductivity, a layer of concrete is frequently used for fireproofing of steel structures. However, concrete itself may be damaged by fire.
Up to about 300 °C, the concrete undergoes normal thermal expansion. Above that temperature, shrinkage occurs due to water loss; however, the aggregate continues expanding, which causes internal stresses. Up to about 500 °C, the major structural changes are carbonation and coarsening of pores. At 573 °C, quartz undergoes rapid expansion due to Phase transition, and at 900 °C calcite starts shrinking due to decomposition. At 450-550 °C the cement hydrate decomposes, yielding calcium oxide. Calcium carbonate decomposes at about 600 °C. Rehydration of the calcium oxide on cooling of the structure causes expansion, which can cause damage to material which withstood fire without falling apart. Concrete in buildings that experienced a fire and were left standing for several years shows extensive degree of carbonation.
Concrete exposed to up to 100 °C is normally considered as healthy. The parts of a concrete structure that is exposed to temperatures above approximately 300 °C (dependent of water/cement ratio) will most likely get a pink color. Over approximately 600 °C the concrete will turn light grey, and over approximately 1000 °C it turns yellow-brown.[17]](Concrete - Wikipedia) One rule of thumb is to consider all pink colored concrete as damaged, and to be removed.
Fire will expose the concrete to gasses and liquids that can be harmful to the concrete, among other salts and acids that occur when fire-gasses get in contact with water.
Hope that helps.
Fire and concrete don’t go well together.
Marcel 
Marcel,
Thanks good info
Barry, The way we usually dealt with fire damage for the plumbing was determined by the media it was run in. Concrete actually protects cast iron from over-heating and chipping, so the standpipes should be okay. Copper is questionable depending on the actual temp reached, a good test is if you can sand the black off and get it to take solder it is okay. Copper in the walls is a different story, usually needs replaced. Don’t have to talk about plastic.