Pore Structure and Moisture Properties of Cement-Based Systemsfrom Water Vapour Sorption Isotherms

Abstract

AbstractThis paper presents results obtained for hardened cement pastes and concretes, ordinary and very-high-performance materials, concerning pore structure and moisture properties.Because of the inadequacy of classical pore investigation methods (mercury intrusion, nitrogenadsorption) to provide the exact pore network characteristics of cement-based systems, notably in the case of very-high-performance materials, a more pertinent type of experiment was carried out: water vapour desorption and adsorption measurements.From these experiments, isotherms were determined at hygrometrical equilibrium and at constant temperature (T = 23 °C) for every desorption/adsorption path. The analysis of these curves gives textural parameters in the mesopore range, not accessible by most of other methods. Thus, from the adsorption curve, the specific surface area accessible to water molecules was calculated by the B.E.T. method. The statistical thickness of the water film adsorbed on the solid surface was also determined. And finally, application of the B.J.H. method on the desorption branch provides relevant porosity values and pore size distribution of the hardened materials, and especially intrinsic characteristics of C-S-H hydrates.This makes it possible to point out the similarities and the differences between the materials, regarding microstructure and moisture properties, and to quantify the influence of mix parameters such as water-cement ratio or silica fume content.