Pore Structure of Hydrated Portland Cement Measured by Nitrogen Sorption and Mercury Intrusion Porosimetry
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PORE STRUCTURE OF HYDRATED PORTLAND CEMENT MEASURED BY NITROGEN SORPTION AND MERCURY INTRUSION POROSIMETRY WILL HANSEN* AND JAMAL ALMUDAIHEEM** *Department of Civil Engineering, University of Michigan, Ann Arbor, Michigan 48109 **Department of Civil Engineering, King Saudi University, Riyadh, Saudi Arabia
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 inThe effect of solvent replacement by trusion porosimetry (MIP) techniques. 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 The 0.4 water-cement ratio paste has pores water-cement ratio pastes. The smaller than can be determined from capillary condensation analysis. volume of pores smaller than 4 nm was estimated from volume-thickness (V-t) For the three systems investigated, the volume of pores greater analysis. For solvent-replaced pastes that showed than 4 nm was obtained by MIP. 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.
INTRODUCTION
Pore structure (i.e. surface area, pore size distribution and pore volume) of hydrated cement is a basic parameter needed to understand important physical and mechanical properties of concrete, including strength, creep, drying shrinkage and durability. These properties are inadequately understood due in part to a lack of a realistic assessment of the pore There is a wide range of pore sizes structure of the hydrated cement. present, typically spanning six to seven orders of magnitude (several No single technique can hundred microns to fractions of nanometers). measure this range, and different techniques yield different values [1]. Other difficulties in assessing pore structure include effects of specimen drying on the original pore structure, and interpretation of results [1-6]. There are limitations to the pore sizes measurable with the nitrogen sorption and MIP techniques. Nitrogen can measure the pores between approximately 0.35 rumand 70 nm, whereas MIP measures the pores between approximately 3.5 nm and 200 pm, depending on the pressure capability of the instrument. Previous studies have discussed the concept of "missing" pore volume Surface areas and porosity measurements using water result in higher [7,8]. values than those obtained by MIP or nitrogen sorption, which require specimen drying before measurement [7,9]. Litvan [4] used solvent replacement with methanol on bottle-hydrated cements (i.e. hydrated cements of high w
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