Analysis of air voids in cementitious materials using micro X-ray computed tomography (µXCT)

Abstract

Air void parameters in cementitious materials are usually identified and analysed manually using image techniques such as incident light microscopy (ILM). The investigative procedure requires considerable effort, and the analysis results can vary between operators. This article presents an approach to the analysis of air void parameters (air void distribution, total and micro air void occurrence, specific surface and spacing/distance factor) in mortars and concretes by using micro X-ray computed tomography (µXCT). By taking the difference in circularity of circle-similar voxel clusters into account, air voids can be distinguished from other pores or cracks with the help of a specialised algorithm. The article gives some recommendations on how the speed and quality of the measurements can be improved by means of refinements in measurement settings and sample preparation. Finally, an approach for determining the threshold (image analysis), which has a significant influence on the results, is presented. A comparison between results from µXCT and ILM make the potential application of this method for determining air void parameters in accordance with EN 480-11 clear.