Flocculation Behavior of Cement Pastes Containing Clays and Fly Ash

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Title: Flocculation Behavior of Cement Pastes Containing Clays and Fly Ash

Author(s): N. Tregger, H. Knai, and S.P. Shah

Publication: Special Publication

Volume: 259

Issue:

Appears on pages(s): 139-150

Keywords: clay; compressive rheology; flocculation; fly ash; green strength; volume fraction

Date: 2/1/2009

Abstract:
The fresh state of concrete is becoming increasingly important in furthering the types of applications in today’s construction world. Processing techniques that have resulted in new technologies such as self-consolidating concrete depend on the microstructural changes within the cement paste during the first hours after mixing and placing. These changes to the microstructure reflect flocculation between particles in suspension. The ability to modify this behavior allows control over the balance between flowability and shape-stability of concrete. This study uses a centrifuge method to determine the relationship between local volume fraction (volume fraction of the sediment region) and compressive yield stress within cement pastes. Based on this relationship, the effectiveness that different admixtures such as clays and fly ash have on the balance between flowability and shape-stability can be measured. Results are consistent with green strength tests performed on example concrete mixes derived from the cement paste mixes.