Admixtures, workability, vibration and segregation: Fid-Bau Portal

Admixtures, workability, vibration and segregation

Betancourt, George Hill

Abstract Segregation and workability of concrete mixes are currently a matter of much concern when concrete admixtures and other types of aggregate are used. This paper attempts to relate the segregation of mixes to viscosity and density of cement paste for a given density of aggregate. Recalling Arquimidae, solids having different densities than the liquid they are placed in float or sink in them. On the other hand, viscous liquids flow with difficulty around solids and hence permit stability given when important differences in densities are present. As far as cement and water, as the liquid phase, are concerned, there is little margin regarding the density of paste and its viscosity since they are closely related to one another—the more water the less viscosity and density of paste; whereas water reducing admixtures (ASTM C-494 Types A and F) as well as certain thickeners, such as Hidroxyetil cellulose, modify the viscosity of the paste without significantly changing its density and so broaden the spectrum of possibilities for mixes as regards workability (related to viscosity) and density (generally accepted to be related to desirable properties). Finally, since a curve can be plotted showing the stability border of mixes in terms of viscosity and densities (of paste and aggregate), vibration which causes liquids to flow and solid particles to move has to be taken into account in order not to segregate mixes, being very stable mixes (those well under the curve) capable of withstanding a large amount whereas mixes close to the border of separation withstand accordingly less.