Date of Award

Fall 2024

Access Type

Thesis - ERAU Login Required

Degree Name

Master of Science in Civil Engineering

Department

Civil Engineering

Committee Chair

Dan Su

First Committee Member

Ashok Gurjar

Second Committee Member

Jeff R. Brown

Abstract

The objective of this research is to enhance the durability of newly constructed structural elements by assessing the performance of various concrete mixes for chloride resistance. The study focuses on establishing and developing correlations between chloride diffusion rates and concrete resistivity. By identifying these correlations and based on the target service life, the research aims to set appropriate thresholds for Surface Resistivity (SR) and Bulk Resistivity (BR) tests, which will be used to qualify concrete mixes used in in extremely aggressive chloride environments. To achieve these objectives, the research uses a systematic approach that combines experimental testing with analytical modeling. Different test methods were used, including Surface Resistivity (SR) based on AASHTO T358, Bulk Resistivity (BR) based on AASHTO TP119, Rapid Migration Test (RMT) based on NT Build 492, and the Bulk Diffusion (BD) test based on ASTM C1556. These tests were conducted on 31 different concrete mixes to evaluate their resistivity, chloride content, and migration characteristics. This array of mixes varied in water-to-cement (w/c) ratios and used different supplementary cementitious materials (SCMs) such as fly ash, slag, silica fume, and metakaolin. The research aimed to correlate the diffusion coefficients obtained from RMT and the BD tests with SR and BR values to establish threshold values that could be indicative of a 75-year service life under high-chloride exposure. The findings from this study demonstrate that the use of SCMs significantly improves concrete durability, by limiting chloride penetration. The Surface Resistivity and Bulk Resistivity tests confirmed that concrete mixes with higher SCM content and lower w/c ratios showed better resistance to chloride ingress. Also, a strong correlation was found between Surface Resistivity and chloride diffusion, with relationship observed between bulk conductivity and non-steady state diffusion coefficient from rapid migration tests, as well as between surface conductivity and non-steady state diffusion coefficients. Additionally, the study successfully established that the 28-day SR and BR test results can reliably predict the results at 56-day, providing an early indicator of long-term durability. These findings enabled the identification of SR and BR thresholds that align with the desired 75-year service life, offering practical guidelines for selecting concrete mixes for use in extremely aggressive chloride environments. Key findings include the following: 1. Correlation of SR and BR with Chloride Diffusion: A strong correlation was established between SR and chloride diffusion coefficients (e.g., Dnssm and D28), with accuracy of R = 0.94 for SR and R=0.93 for BR. These correlations enable the prediction of diffusion coefficients from resistivity measurements. 2. Predicting Long-Term Resistivity: The study demonstrated that 28-day SR and BR results reliably predict 56-day values, with accuracy of R=0.97 for SR and R=0.97 for BR. 3. Threshold Development for 75-Year Service Life: Using the Life-365 software and correlating resistivity with service life predictions, SR and BR thresholds were 5 identified for different concrete cover depths. For instance, an SR threshold of 48.86 kΩ-cm and BR threshold of 22.21 kΩ-cm were determined for a 2.5-inch cover depth. The implications of this research are profound for the construction industry, particularly for regions with high chloride exposure conditions. By providing a clear framework for developing concrete mixes with enhanced durability, the study supports the Florida Department of Transportation's (FDOT) objectives to optimize concrete performance and extend the service life of infrastructure. The findings contribute to the advancement of concrete technology by establishing robust testing methods and performance benchmarks, ultimately leading to more durable and cost-effective concrete structures.

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