Use of Chemical Admixtures to Modify the Rheological Behavior of Cementitious Systems Containing Manufactured Aggregates

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Title: Use of Chemical Admixtures to Modify the Rheological Behavior of Cementitious Systems Containing Manufactured Aggregates

Author(s): A. Jeknavorian, K. Hazrati, A. Bentur, H. Koyata, D. McGuire, and P. Sandberg

Publication: Special Publication

Volume: 239

Issue:

Appears on pages(s): 15-30

Keywords: aggregates; petrographic analysis of aggregates; rheology; viscosity-modifying agent; yield stress

Date: 10/1/2006

Abstract:
Aggregate shape, texture, and grading have been known to have a significant effect on the rheological performance of fresh concrete. Moreover, while the optimization of aggregate selection can provide both technical and economical benefits, the availability of materials and construction operations can often dictate the use and proportioning of certain aggregate sources, such as manufactured sands, which can adversely impact the rheology of cementitious mixtures. The use of certain chemical admixtures has been found to often minimize the need to increase cement and water contents in order to overcome the loss of workability that can accompany aggregate sources which feature flat, elongated, angular, and rough particles. In this study, a wide range of natural and manufactured sands, characterized for gradation, mineralogy, shape, texture, and cleanliness, are evaluated for their effect on mortar rheology, with and without a viscosifying-type chemical admixture. While associations between aggregate characteristics and their impact of mortar rheology may not be readily evident, the ability of this class of admixture can be shown to mitigate the rheological effect of certain sands, and in some cases allow for optimizing the mixture to lower paste contents.