Abstract:

The dissertation research work presented herein consists of two separate findings: one investigates a potential new coating technique that could be used to rehabilitate deteriorated concrete sewer pipes, and the other researches inducing electrical conductivity into geopolymer concrete to serve as smart material by being able to sense stress changes. Both applications utilize electricity to enhance the performance and/or functionality of hardened cementitious materials.

Microbiologically induced corrosion (MIC) in concrete wastewater conveyance systems is a leading deterioration mechanism in such structures. This work focuses on breaking the MIC cycle by preventing colonization of the bacteria responsible for converting hydrogen sulfide to sulfuric acid. Electrokinetics was used to drive an antimicrobial agent (cuprous oxide) into the porous wall surface of a pre-cast concrete pipe. An electric potential difference applied between the steel reinforcement embedded in the concrete and a copper electrode placed in the coating solution provides the driving force to the copper ions. Atomic absorption tests performed on the coated specimens were used to determine the percentage of cuprous oxide that penetrated the porous surface and migrated into the hardened concrete matrix. A pilot study conducted on three mock pipe specimens demonstrated that the process is effective on partially corroded and non-corroded pipes. Test data also revealed that the amount of copper that migrated into the concrete matrix is time dependent. Based on the preliminary test results, a treatment procedure was designed and implemented on a 15" diameter commercial pre-cast concrete pipe. The data suggest that the method could be reemployed to "immunize" new and partially deteriorated steel reinforced concrete pipes against MIC.

Geopolymer concrete is finding a growing number of niche applications in the field of civil engineering due to its high compressive strength, strength gain rate, fire resistance, maintenance of structural properties in elevated temperature environments, chemical stability in highly acid environments, and relatively low cost and environmental benefits. Electrically conductive geopolymer could serve as a new smart material that could monitor its own health. Typically, health monitoring in structures is done by assessing their state of stress. One such method involves monitoring electrical resistance variations as an indirect indication of the stress variations in the structure. Carbon fibers were added to a fresh geopolymer mix to enhance its electrical conductivity. AC-impedance spectroscopy analysis was performed on sample specimens to obtain their electrical resistance. Results from the preliminary phases demonstrated that geopolymer exhibits superior performance to OPC-made concrete as a conductor of electrical current. Conductive geopolymer concrete specimens containing an optimum percentage of carbon fibers were dynamically loaded to observe the changes in electrical resistance. Data obtained from the dynamic test suggests that conductive geopolymer could serve as a smart material.