Analysis of cement-bonded materials by multi-cycle mercury intrusion and nitrogen sorption

The pore systems of cement-based materials are studied by N(2) sorption and mercury intrusion porosimetry (MIP). Pore size distributions and internal surfaces are derived. Especially in materials with a broad pore size distribution, these (and other) methods generally do not lead to coincident results. It is shown here, how the interpretation of the experimental data of the two methods may be modified in order to obtain coincident pore size distributions from both methods. The studied pore systems are described as array of chambers which are connected by smaller throats. N(2) adsorption is used to calculate the size of the pores, whereby no distinction between throat or chamber type is possible with this method. Assuming mercury entrapping in ink-bottle type pores (pores that are connected to an external surface through smaller pores only) being the dominant process for mercury snap-off during extrusion and applying multi-cycle MIP, the calculation of the size of the entrances of these ink-bottles is possible. It is shown that similar results also may be derived from mercury extrusion data by applying a contact angle correction for the retracting mercury meniscus. A good agreement of the pore size distribution of the connected, non-ink-bottle type pores derived from either N(2) sorption or mercury intrusion is obtained. Samples of cement paste and mortar are analysed. A significant difference between cement paste and mortar regarding the neck entrances of ink-bottle type pores is found and attributed to the coarse pore space around the aggregates, the interfacial transition zone.