Estimating the permeability of cement pastes and mortars using image analysis and effective medium theory

• Published in: Cement and concrete research 2012-02, Vol.42 (2), p.476-483
• Main Authors: Wong, H.S., Zimmerman, R.W., Buenfeld, N.R.
• Format: Article
• Language: English
• Subjects: Applied sciences; Backscattered electron imaging (B); Buildings. Public works; Cement concrete constituents; Cements; Concretes. Mortars. Grouts; Exact sciences and technology; General (composition, classification, performance, standards, patents, etc.); Hydraulics; Image analysis (B); Materials; Mathematical analysis; Mortars; Permeability; Permeability (C); Porosity; Porosity (B); Properties and test methods; Properties of anhydrous and hydrated cement, test methods; Sand; SEM (B)
• ISSN: 0008-8846; 1873-3948
• DOI: 10.1016/j.cemconres.2011.11.018

A method to estimate permeability of cement-based materials using pore areas and perimeters from SEM images is presented. The pore structure is idealised as a cubic lattice having pores of arbitrary size. The hydraulic conductance of each pore is calculated using the hydraulic radius approximation, and a stereological factor is applied to account for the random orientation of the image plane. A ‘constriction factor’ is applied to account for variations in pore radius along the pore axis. Kirkpatrick's effective medium equation is then used to obtain an effective pore conductance, from which the macroscopic permeability is derived. The method was tested on forty-six pastes and mortars with different w/c ratio, cement, age and sand content. The permeabilities ranged from 3×10−18m2 to 5.8×10−16m2. It was found that 76% of the permeabilities were predicted to within a factor of ±2, and 98% within a factor of ±5 from measured values.