Determination of air-void parameters of hardened cement-based materials using X-ray computed tomography

This paper presents an attempt to tackle limitations in the two-dimensional (2D) stereological characterization of the air-void parameters of hardened cement-based materials by employing three-dimensional (3D) X-ray computed tomography (CT), a technique capable of simultaneously imaging numerous sections within a specimen. Using three hardened cement paste specimens composed of different air-void systems, we performed sensitivity analyses in terms of the number of traverse lines employed for a single section and the number of sampling sections across the height of a specimen. Parameters for a single section converged rapidly as the number of traverse lines increased, although unacceptable variations were in evidence across multiple sections. When the number of sampling sections exceeded about 10, a set of representative air-void parameters was successfully obtained within a standard variation of less than 10% of average values. The spacing factor and air content measures obtained via CT image analysis were in good agreement with previously reported data and with the original spacing factors defined for 3D space. Some advantages found in the use of X-ray CT imaging for determining air-void parameters are discussed. (C) 2012 Elsevier Ltd. All rights reserved.