Mercury porosimetry - An inappropriate method for the measurement of pore size distributions in cement-based materials

The conditions that must be met for mercury intrusion porosimetry (MIP) mea surements to provide valid estimates of the pore size distribution of porou s solids are reviewed. Evidence is presented indicating that these conditio ns are not satisfied in cement-based systems. In cement-based systems, near ly all of the mercury intrusion is held up until pressure corresponding to the threshold diameter is reached; subsequently, large and small pores are filled indiscriminately. Air voids, in sizes up to several hundred micromet ers, are present in most pastes in substantial volume, unless the pastes we re mixed under vacuum; these air voids are also not intruded until the thre shold pressure is reached, and are recorded as fine (ca. 0.1 mum) pores. It is concluded that MIP measurements are useful only to provide threshold di ameters and intrudable pore space measurements, which can serve as comparat ive indices for the connectivity and capacity of the pore systems in hydrat ed cements. MIP measurements should be abandoned as measures of the actual pore sizes present. (C) 2000 Elsevier Science Ltd. All rights reserved.