Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Department

Civil Engineering

First Advisor's Name

Atorod Azizinamini

First Advisor's Committee Title

Committee Chair

Second Advisor's Name

Nakin Suksawang

Second Advisor's Committee Title

Committee member

Third Advisor's Name

Ton-Lo Wang

Third Advisor's Committee Title

Committee member

Fourth Advisor's Name

Arindam G. Chowdhury

Fourth Advisor's Committee Title

Committee member

Fifth Advisor's Name

Arvind Agarwal

Fifth Advisor's Committee Title

Committee member

Keywords

Concrete, Sulfate Attack, Acid Attack, Scanning Electron Microscopic, Energy-Dispersive X-Ray Spectroscopy, Microstructures, Cracks, Accelerated Test, Image Processing, Regression Analysis

Date of Defense

9-1-2015

Abstract

Concrete substructures are often subjected to environmental deterioration, such as sulfate and acid attack, which leads to severe damage and causes structure degradation or even failure. In order to improve the durability of concrete, the High Performance Concrete (HPC) has become widely used by partially replacing cement with pozzolanic materials. However, HPC degradation mechanisms in sulfate and acidic environments are not completely understood. It is therefore important to evaluate the performance of the HPC in such conditions and predict concrete service life by establishing degradation models.

This study began with a review of available environmental data in the State of Florida. A total of seven bridges have been inspected. Concrete cores were taken from these bridge piles and were subjected for microstructural analysis using Scanning Electron Microscope (SEM). Ettringite is found to be the products of sulfate attack in sulfate and acidic condition.

In order to quantitatively analyze concrete deterioration level, an image processing program is designed using Matlab to obtain quantitative data. Crack percentage (Acrack/Asurface) is used to evaluate concrete deterioration. Thereafter, correlation analysis was performed to find the correlation between five related variables and concrete deterioration. Environmental sulfate concentration and bridge age were found to be positively correlated, while environmental pH level was found to be negatively correlated.

Besides environmental conditions, concrete property factor was also included in the equation. It was derived from laboratory testing data. Experimental tests were carried out implementing accelerated expansion test under controlled environment. Specimens of eight different mix designs were prepared. The effect of pozzolanic replacement rate was taken into consideration in the empirical equation. And the empirical equation was validated with existing bridges.

Results show that the proposed equations compared well with field test results with a maximum deviation of ± 20%. Two examples showing how to use the proposed equations are provided to guide the practical implementation. In conclusion, the proposed approach of relating microcracks to deterioration is a better method than existing diffusion and sorption models since sulfate attack cause cracking in concrete. Imaging technique provided in this study can also be used to quantitatively analyze concrete samples.

Identifier

FIDC000151

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