Reference: D.N. Winslow, M.D. Cohen, D.P. Bentz, K.A. Snyder, and E.J. Garboczi, Cement and Concrete Research 24, 25-37 (1994).
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D.N. Winslow and M.D. Cohen
School of Civil Engineering
Purdue University
West Lafayette, Indiana 47907
D.P. Bentz, K.A. Snyder, and E.J. Garboczi
National Institute of Standards and Technology
Building Materials Division, 226/B350
Gaithersburg, MD 20899
Abstract
The cement paste in concrete and mortar has been shown to have a pore size distribution different than that of plain paste hydrated without aggregate. For mortar and concrete, additional porosity occurs in pore sizes larger than the plain paste's threshold diameter as measured by mercury intrusion. Based on the assumption that these larger pores are essentially present only in the interfacial zones surrounding each aggregate, an experimental program was designed in which the volume fraction of sand in a mortar was varied in a systematic fashion and the resultant pore system probed using mercury intrusion porosimetry. The intrusion characteristics were observed to change drastically at a critical sand content. Similar results were observed for a series of mortar specimens in which the cement paste contained 10% silica fume. To better interpret the experimental results on mortars, a hard core/soft shell computer model was developed to examine the percolation characteristics of these interfacial zone pores. Using the model, interfacial zone percolation in concretes was also examined. The implications of interfacial zone percolation for transport properties and durability of mortar and concrete are discussed.
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