Effect of carbonation on cement paste microstructure characterized by micro-computed tomography

•Microstructural changes in cement paste from carbonation are investigated through image analysis of microstructures obtained from a synchrotron micro-CT.•Porosity reduction after carbonation is captured from the image analysis.•The grayscale values (linear attenuation coefficient) of micro-CT images are reduced after carbonation.•The grayscale values of micro-CT images do not necessarily increase although the material density increases after carbonation as can be confirmed by the theory. The carbonation of cement paste changes its microstructural characteristics. The porosity of the cement paste microstructure is reduced when calcite is produced from the reaction between portlandite and carbon dioxide. In this study, such microstructural changes were investigated using image analyses of the 3D microstructures obtained with synchrotron micro-computed tomography (CT). When two sets of samples were subjected to different degrees of carbonation, the porosity and pore size reductions were identified from the micro-CT images. The formation of calcite caused by the reaction of portlandite was indirectly identified by the reduction of the mean grayscale value or linear attenuation coefficient (LAC) of the solid phase voxels. It was confirmed that micro-CT could also be used as a supplementary tool for the analysis of the microstructural evolution of cement paste under carbonation.