Socket where a sand grain has been pulled away from cement paste in 1-day
old mortar. The sand grain was originally at the top of the picture. Note
the open structure and the presence of crystals of calcium hydroxide in this
region. "In portland cement mortars, the microstructure of the interfacial
zone, extending to about 20 to 50 æm from the sand grain surface, is
significantly different from that of the bulk paste matrix away from the
sand grain. It is characterized by a massive CH layer engulfing the sand
grain and by some channel type gaps." "The formation of this zone may be the
result of the presence of some water-filled gaps around the sand grains in
the fresh mortar. These gaps may be the result of bleeding and inefficient
filling with cement particles of the 20-æm space around the grain surface."
Arnon Bentur and M. D. Cohen, "Effect of Condensed Silica Fume on the
Microstructure of the Interfacial Zone in Portland Cement Mortars," Journal
of the American Ceramic Society, Vol. 70, No. 10, pp. 738-743, 1987.
The Silica Fume Association
38860 Sierra Lane, Lovettsville, VA 20180
Tel: 540.257.4224 Fax: 540.822.9456
