Collaborative Research: Photocatalytic NOx Oxidation and Ion Exchange: New Strategies Towards Functional Corrosion Resistant Concrete Infrastructure

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Reinforced concrete structures exposed to sea water or de-icing salts are susceptible to the corrosion of embedded steel, due to the ingress of chloride ions. Such corrosion results in deterioration, reduces the service-life of structures, and poses a burden to the national economy. In spite of extensive efforts, our current methods of corrosion protection remain either: too expensive, or unable to prevent corrosion actions. This research develops a new strategy that utilizes visible light to decompose air pollutants into chemical agents that can suppress steel corrosion in concrete structures. Such environmentally sustainable solutions are critical to maintain large, widespread and durable infrastructure?a critical driver of economic growth. To support these goals, the research trains a diverse technical workforce at the levels of: post-doctoral scientists, Ph.D. and undergraduate students and high-schoolers at both University of California-Los Angeles and Georgia Tech. Both university groups cross-train with each other, hierarchically and functionally to foster collaboration and exchange scientific advancements needed to preserve infrastructure inventories. The multidisciplinary nature of the work will expose young researchers to cross-cutting intellectual concepts relevant to sustainable development and propelling new technologies to the marketplace. This research exploits the photoactive behavior of titanium dioxide nanoparticles, and uses visible light, and manipulations of the cement chemistry, to prevent steel corrosion in reinforced concrete. Monosulfate (AFm) phases produced during cement hydration have the ability to intercalate anions in their structure in a preference described as: chloridenitratenitritecarbonatesulfatehydroxide. Thus, cements can be tuned to maximize AFm formation, and capture of chloride species intruding into concrete. Further, up on exposure to light, titanium dioxide can convert atmospheric pollutants in the form of nitrogen oxides to aqueous nitrate/nitrite ions which serve as anodic corrosion inhibitors. When applied in conjunction with each other, these processes work to trap intruding chloride ions within the AFm phase while simultaneously releasing nitrate/nitrite ions (previously stored in the AFm) into the pore solution to ensure steel corrosion inhibition. Towards these objectives this research: (1) synthesizes visible light active titanium dioxide, (2) optimizes cement chemistry to maximize the yield of AFm phases and (3) simulates nitrite/nitrate/chloride transport in concrete to maximize steel corrosion inhibition. The intellectual outcomes of this work include: novel advancements in corrosion inhibition methods which exploit photocatalytic behavior, thermodynamic selectivity and ion exchange preference as a means towards designing regenerative and tunable corrosion protection systems for concrete infrastructure.