A reassessment of mercury intrusion porosimetry by comparison with H-1 NMR relaxometry

This paper shows how MIP measurements can give an accurate picture of the capillary porosity of cement pastes. Regions of the intrusion curves can be identified corresponding to capillary or gel pores. The amount of capillary pores is in excellent agreement with the values measured by Muller et al. [Densification of C-S-H measured by H-1 NMR relaxometry, J. Phys. Chem. C. 117, 2013; Use of bench-top NMR to measure the density, composition and desorption isotherm of C-S-H in cement paste, Micro. Meso. Mater 178, 2013] in H-1 NMR studies of similar mixes studied in undried conditions. Our investigations on the different drying methods indicate that only the solvent exchange method adequately preserves the sample porosity. The quantitative MIP analysis shows that MIP measures, for the mixes studied, all capillary pores and, in some cases, a small fraction of C-S-H gel pores. Comparison of pore sizes between MIP and H-1 NMR indicates that a contact angle of 140 degrees usually used in the Washburn equation is most likely overestimated. We suggest that a more appropriate contact angle is 120 degrees.