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An essential requirement of concrete for any use is that it be transported from mixer to forms without separation of water, cementing materials, or aggregates, with sufficient retention of consistency to permit economical consolidation. To achieve that end, it is an objective in proportioning the ingredients of concrete to obtain a blend of solid materials, from the finest cement grain to the largest particle of coarse aggregate, which, when consolidated, will have an interstitial void structure of minimum volume, and relatively low permeability and surface area. The latter requirements would appear to be contradictory since permeability of a bed of granular solids is inversely related to its surface area. Permeability of the aggregate void system should be low enough to prevent permeation by water or cement paste under pressure. Surface area should be low enough to permit the use of economical amounts of cement and suitable water/cement (w/c) ratios to provide a volume of paste sufficient to saturate the aggregate voids and form workable cohesive concrete.
Principal, Valore Research Associates, Ridgewood, N.J.