When buildings have nothing in them but concrete, they don't burn well. However, many humans find this discomforting, so they bring lots of flammable material into the building.
Building design takes into account questions like:
How can you structure the rooms and activities so as to minimize the amount of tinder in the building?
What building designs help you compartmentalize fires?
What suppression techniques can you use?
NIST has a paper on the flammability characteristics of painted concrete with the following chart pointing out that building maintenance also must understand the need to not slowly load the building with kindling over time.