Three significant factors diminish the bearing capacity of the structure and hamper stability in the event of a tunnel fire:
Explosion-like spalling caused by immense heat development and the resultant chemical and physical processes triggered in the concrete. Modern high-strength concretes, whose pore content and permeability are reduced, react especially sensitively here.
Changes in the structure of the aggregate filler containing quartz caused by heat (the so-called quartz leap) result in changes in volume and thereby in concrete attrition.
Tiny cracks caused by the fire impact increasingly...