Post-Fire Assessment of Concrete in Bridge Decks

In recent years, there have been a number of truck fires involving bridges with concrete components. If the fire burns for a significant period of time, the structural integrity of concrete components could be damaged due to fire. Research-based guidance for evaluating the level of fire damage is currently unavailable and would be beneficial for post-fire bridge inspectors.

This research project focused on evaluating the effects of fire induced damage on concrete bridge deck elements. In order to achieve this goal, a series of controlled heating experiments and material analysis were conducted. Two concrete bridge deck specimens from the I-469 bridge over Feighner Road were heated for different time durations (40 - 80 min.) following the ISO-834 temperature-time curve. The deck specimens were cooled naturally after the specific heating durations. The temperature profiles through the depth of deck specimens were measured during heating and cooling. After testing, concrete samples were taken from the deck specimens for material analysis. Different types of material tests were conducted on samples taken from the undamaged and damaged deck specimens. The material test results were used to evaluate the effects of fire induced damage on the concrete microstructure, and to correlate the microstructure degradation with the through-depth temperature profiles of deck specimens.

From the experimental results, several critical parameters that can affected by fire temperature and duration were discussed: (i) through-depth temperature profiles of deck specimens, (ii) cracks on the exposed surface of deck specimens, (iii) color changes of deck specimens, (iv) microstructure of heated concrete samples, (v) content of calcium hydroxide in fire damaged concrete samples at various depths. Based on the results from heating experiments and observations from material analysis, recommendations and guidance for evaluating concrete decks subjected to realistic fire scenarios are provided to assist bridge inspectors.