Influence of Bridge Fires on the Properties of Concrete and Steel Components

Concrete and steel specimens were collected from control (unexposed) and fire-exposed sections of highway bridges in the state of Indiana, U.S., to evaluate the degree of degradation of selected properties of concrete and steel components. The changes in the properties of concrete were evaluated using differential scanning calorimetry (DSC) and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) techniques. The focus of concrete evaluation was on detection and quantification of calcium hydroxide (CH), identification of changes in the quality and quantity of other hydrates, assessment of the extent of cracking in the matrix, and the occurrence of debonding of aggregates. Concrete collected from the sections of bridges exposed to fire was found to contain lower amounts of CH compared with the concrete from the control (i.e., not exposed) sections. The observed degree of cracking and aggregate debonding was also higher in specimens exposed to fire. Steel specimens were evaluated with respect to changes in the microstructure (the size and the pattern of the grains) and hardness. No significant changes resulting from fire exposure were detected.