Analysis of the effect of heating and re-curing on the microstructure of high-strength concrete using X-ray CT

•We used X-ray CT to examine the effect of heating and re-curing on microstructure.•Heating caused an increase in total pore space due to an increase in connectivity.•Cracks in the mortar–aggregate interface and bridging cracks occurred due to heating.•Water re-curing was effective for reducing connectivity and recovering microstructure.•Most microstructure recovery occurred within 7 days of water re-curing.

Microstructure recovery plays an important role in restoring the performance of concrete damaged by fire. This research applied X-ray CT and image analysis techniques to non-destructively examine the internal microstructure of high-strength concrete in order to clarify the effects of heating and re-curing on microstructure characteristics. Heating caused an increase in total pore space due to an increase in connectivity caused by the formation of cracks in the mortar–aggregate interface and bridging cracks. Water re-curing, however, was effective in recovering microstructure through the reduction in connected pore space, with most recovery occurring within 7 days.