Schematic of the transition zone. Note that in the area adjacent to the
surface of an aggregate particle, the relatively uniformly sized cement
grains are not packed as densely as they are in the bulk zone. This "wall
effect" is one of the reasons stated for the relative weakness and
permeability of cement paste in the transition zone.
When silica fume is added to the concrete, better particle packing occurs in
this area. The silica fume in this area can further refine the transition
zone through its pozzolanic reaction.
This sketch is taken from H. H. Bache, "Densified Cement/Ultra-Fine
Particle- Based Materials," Presented at the Second International Conference
on Superplasticizers in Concrete, 1981.
The Silica Fume Association
38860 Sierra Lane, Lovettsville, VA 20180
Tel: 540.257.4224 Fax: 540.822.9456
