Investigation on Carbonation Induced Meso-Defects Changes of Cement Mortar Using 3D X-Ray Computed Tomography

In order to investigate the defect changes of cement mortar due to carbonation,X-ray computed tomography(XCT) was employed to quantitatively analyze three dimensional(3D) meso-defect volume distribution changes of cement mortar before and after carbonation.The high-resolution 3D images of microstructures and filtered defects were reconstructed by XCT VG Studio MAX 2.0 software.The meso-defect volume fractions and size distribution were analyzed based on 3D images via add-on modules of 3D defect analysis.The results indicate that 3D meso-defect volume distributions are from 0.03 to 5.5 mm3,and the meso-defect volume fractions before and after carbonation are 2.79% and 1.86%,respectively.After carbonation,the smaller defects decreased signifi-cantly,compared to the bigger defects,in particular between 0.03–0.1 mm3.The main reason was calcium carbonate and water,which were generated by carbonation.The molar volume of calcium carbonate was larger than that of calcium hydroxide and CSH gel.Therefore,the new generated calcium carbonate and water could fill and refine some defects.