Date on Master's Thesis/Doctoral Dissertation

12-2017

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Civil and Environmental Engineering

Degree Program

Civil Engineering, PhD

Committee Chair

Sun, Zhihui

Committee Co-Chair (if applicable)

Rockaway, Thomas

Committee Member

Rockaway, Thomas

Committee Member

Kim, Young Hoon

Committee Member

Fu, Xiao-An

Author's Keywords

rheology; thixotropy; diatomaceous earth; concrete; fresh properties

Abstract

During construction, concrete goes under various operations. It is normally transported to the job site, be placed and consolidated in the formwork, etc. The easiness and quality of these operations are very much related to the intrinsic rheological properties of concrete. Therefore, a good understanding of rheological behavior of concrete under various conditions are needed. Thixotropy is an important part of rheology. The thixotropic behaviors of concrete can be good representatives of its flow behaviors on the job site. For example, the breakdown aspect of thixotropy can help to explain how its flow behavior can impact concrete pumping and its buildup aspect can help to estimate the lateral pressure on formwork and concrete resistance to segregation. Thus, good understanding of thixotropic behaviors of concrete can help to understand and predict flow behaviors of concrete in practice. Researchers have realized the importance of thixotropic behavior of concrete, however, there is no agreement on the measuring protocol of this parameter. This leads to the goal of this research, which is to propose a comprehensive series of protocols that can make quantitative measurements on both breakdown and buildup aspects of thixotropic behaviors of concrete. While measuring breakdown and buildup separately, the correlations between these two aspects have also been investigated. On top of the developed measuring protocol, a new analytical model on thixotropic behavior of cement paste is also proposed. With the proposed model, the influences of raw material characterizations and ambient condition on internal structural development in cement paste can be systematically studied. To simulate the real on-site conditions, parameters such as pressure and temperature which influence rheological properties are also considered.

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