Comparative Assessment of Pore Structure and Water Retention in Concrete Using MIP, CT, SEM, and Dewpoint Techniques

Abstract

Understanding water retention and pore structure in concrete is essential for modeling unsaturated flow and assessing long-term durability, particularly in containment and deep foundation structures. This study investigates two concrete mixtures with different water-to-cement (w/c) ratios (0.40 and 0.50) using a multi-method approach. Water retention curves (WRCs) were measured with a chilled-mirror dewpoint potentiometer and fitted using the Fredlund–Xing model. Pore structures were analyzed via mercury intrusion porosimetry (MIP), X-ray computed tomography (CT), and scanning electron microscopy (SEM). Results show that the mixture with the lower w/c ratio exhibits a higher proportion of fine pores, while the higher w/c ratio leads to a broader pore size distribution and a flatter WRC. MIP-based WRC estimations provided a rough approximation but consistently underestimated measured retention values. CT and SEM revealed distinct pore size domains, with pore size distributions fitting better to a lognormal model than to a Weibull distribution. Although each technique offers only partial insight, their combined application allows for a more comprehensive understanding of concrete's pore network and its effect on hydraulic behavior. The findings highlight both the potential and the limitations of using indirect pore structure data to estimate water retention characteristics in cementitious materials.