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https://hdl.handle.net/2142/83438
Description
Title
Concrete Rheology
Author(s)
Szecsy, Richard Samuel
Issue Date
1997
Doctoral Committee Chair(s)
Dissertation Abstracts International, Volume
Department of Study
Civil Engineering
Discipline
Civil Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Civil
Language
eng
Abstract
The rheology of concrete is investigated in this work. The method involves using a partial experimental matrix that considers the effects of sand content, water/cement ratio, coarse aggregate type, fly ash content and the addition of a superplasticizer on the rheological parameters of yield stress, plastic viscosity, and apparent viscosity. The objective of this work was not only to measure the effects on rheology by the variables, but also to predict some of the same measured rheological parameters. The modeling of yield stress and apparent viscosity for concrete was accomplished by measuring the same rheological parameters for cement paste along with various aggregate parameters for the concrete. From the variables used it was concluded that sand content had the greatest impact on the yield stress and viscosity. A minimum yield stress and viscosity were produced at an intermediate sand content. Other significant effects were from the aggregate type and shear rate. Two coarse aggregate types were used: river gravel and limestone. They were classified based on their circularity, which is a ratio of area and perimeter as taken from a digital image of each individual aggregate. In all cases the lower the circularity of the coarse aggregate the higher the rheological values of yield stress and viscosity. Another important finding was that many effects depend on shear rate. At higher shear rates many of the investigated variables had small effects, whereas at lower shear rates variables had large effects. Using the Krieger-Dougherty model, it was possible to predict the rheology of concrete from paste viscosity and properties of the aggregate. Additionally, an empirical model created from this research successfully predicted the yield stress for concrete from the yield stress of the paste and certain aggregate parameters. As a final result a process is suggested for mix design based on rheology.
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