Date of Award

Spring 2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil Engineering

First Advisor

Carlos Montes-Montoya

Abstract

The manuscript presented herein is based on the investigation of the short and long term properties of fly ash based geopolymer concrete (GPC) and their link to fly ash characteristics. Fly ash (FA) exhibits a significantly different particle morphology, which impacts the mechanical properties of the resulting GPC and typically contains impurities that fluctuate from one FA source to another. A key contribution of this research work is the capturing of the variability posed by the FA stockpile with a wide range of physical, chemical, and crystallographic characteristics as a source material to select the GPC mix design. In the case of prestressed GPC application, there are concerns on prestress loss caused by elastic shortening, shrinkage, and creep. Thus, the values of mechanical strength, ultimate shrinkage strain, and creep coefficient of the GPC have to be estimated reasonably and accurately at the design stage to avoid any loss of structural capacity the premature structural failure.

The test study was conducted to evaluate the mechanical strength of fly ash based geopolymer concrete. Fly ash samples from different sources were tested to see the impact of the chemical and physical properties of the FA element on the fresh and hardened properties of the GPC. Samples from 50 different power plants were collected and analyzed to develop the regression equation. The empirical model was developed to predict the flexural strength from the compressive strength, the unit weight from the density of the FA, the elastic modulus from the unit weight, and compressive strength of the GPC and the compressive strength from the chemical and physical properties of the FA. A second set of 10 FA samples was selected randomly to validate the test results. It was observed that the prediction equation is accurate within 5 to 7 percent of the experimental values. The restrained shrinkage and free shrinkage test was conducted to observe the shrinkage of the GPC. Free shrinkage of the GPC plot was compared with the available empirical model for compatibility. In this study, an apparatus was designed to determine the creep of the GPC and an effective creep testing procedure was developed and documented. Experimental results obtained from this study were compared with the available empirical models.

The results obtained from this study show that the compressive strength of the GPC can be presented with reasonable accuracy by analyzing the physical and chemical property of the FA. Also, it was found that the mechanical behavior of the GPC can be predicted with the equations given in the American Concrete Institute's Building Code (ACI 318, 2008) with minor modifications. Experimental results obtained from this study were compared with the available empirical models. It has been observed that the free shrinkage strain and creep compliance prediction equations for the GPC are akin to those given in the SAKATA model and GL 2000 model.

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