Pore Structure of Hydrated Portland Cement Measured by Nitrogen Sorption and Mercury Intrusion Porosimetry

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Abstract
The pore structure (i.e. surface area, pore size distribution and pore volume) of well-hydrated portland cement pastes of water-cement ratios 0.4, 0.6, and 0.75 were investigated by the nitrogen sorption and mercury intrusion porosimetry (MIP) techniques. The effect of solvent replacement by methanol on the pore structure was studied as well. It was concluded that the solvent replacement drying procedure preserves the original pore structure of hydrated cement because the calculated and measured bulk densities of the different water-cement ratio systems investigated were in excellent agreement. Capillary condensation analysis was used to estimate the volume of capillary pores smaller than 4 nm in pore diameter for the 0.6 and 0.75 water-cement ratio pastes. The 0.4 water-cement ratio paste has pores smaller than can be determined from capillary condensation analysis. The volume of pores smaller than 4 nm was estimated from volume-thickness (V-t) analysis. For the three systems investigated, the volume of pores greater than 4 nm was obtained by MIP. For solvent-replaced pastes that showed capillary condensation according to V-t analysis, excellent agreement was obtained between the nitrogen sorption and MIP techniques in the pore diameter range of 4 nm to 30 nm.