Detecting Microstructural Changes in Concrete Conditioned Under Thermo-mechanical Loading using X-ray Computed Tomography

The combined action of thermal and mechanical loading in nuclear applications can affectthe pore structure of concrete. It is important to characterise these changes in order tounderstand the effects they may have on material strength and durability. Common methodsof microstructural analysis such as electron microscopy can fail to capture representative data. To overcome this, 3D X-ray Computed Tomography (XCT) has been used to investigatemicrostructural changes in concrete specimens from a research program on Advanced Gascooled Reactor (AGR) pressure vessels which were subjected to hydrostatic mechanicalloading and thermal treatment. Cylindrical cores extracted from the specimens werecharacterised non-destructively using XCT at the Henry Moseley X-ray Imaging Facility(HMXIF), University of Manchester. Analysis of the reconstructed XCT data for 14.6 μmresolution scans has revealed significant changes in the pore size distribution of heatedspecimens with respect to that of unconditioned control specimens. Whilst changes in poresize distribution due to hydrostatic mechanical load cannot be clearly identified, those specimens conditioned under combined thermo-mechanical loading experienced a greater change than those conditioned using thermal treatment only.