Microstructures of fire-damaged concrete

Abstract

This paper presents results of scanning electron microscopy (SEM) and stereo microscopy investigations of fire-damaged concrete. Samples were either taken from concrete that was subjected to heating and cooling of controlled temperatures in the laboratory or removed from concrete and masonry units exposed to fires in the field. By compiling SEM photographs, a clear chronological pattern of a failure mechanism can be visualized. For instance, the morphologies of hydrates from room temperature up to 900 C and reformation of calcium hydroxides (CH) during cooling all have distinguished morphological appearances of their own. Such visual information that would otherwise be impossible to see with the naked eye will help scientists and engineers understand concrete behaviors in fire. This study has focused on microstructures of cement pastes/aggregates, microvoids/cracks, and separation of the cement paste from aggregates in heated concrete samples. An application of lincrete, a type of polyester-polymer concrete developed at National Chiao Tung University, is included to demonstrate the use of a cement-based polymer mortar in the rehabilitation process of fire-damaged concrete.