Concrete is used heavily in shielding of nuclear power plants, and storage of nuclear waste. In such environments, exposure to radiation is inevitable. While concrete is optimal for shielding such radiation from the outside (due to its water content), collision of high energy radiation with the aggregates (i.e. rocks and gravel bound together by cement) can lead to amorphization and increases in reactivity. When this radiation damage occurs for aggregates containing silica, the result is alkali-silica reaction (ASR). ASR is commonly known to result in expansion, cracking, and ultimate failure of the concrete. This research uses molecular dynamics simluations, which model physical movement of atoms and molecules, to assess the extent and nature of this radiation damage. Results provide a basis for developing mitigation strategies to prevent ASR from occurring in concrete exposed to radiation.
Silicate materials are abundant in both nature and industry as quartz and other minerals, cementitious binders, and glasses. In any of these contexts, it is important to understand how reactive (i.e. fast dissolving) or durable (i.e. slow dissolving) a given silicate material may be. This research considers such problems using topological constraint theory. This theory operates on the idea that the number of constraints (i.e. connections via atomic bonds) determines how easily a material will dissolve. Results provide a means to formulate both more durable glasses and more reactive supplementary cementing materials, as well as predict other properties which may depend on silicate dissolution-precipitation processes such as concrete creep.
Ceramic materials have myriad applications in modern technology. Cementitious ceramics, such as tricalcium silicate and mayenite, are some of the most common such materials, found in cement, mortar, and concrete. Tricalcium silicate is the main phase of cement, and its reactivity dictates the performance of construction materials in buildings, bridges, and pavements across the globe. Mayenite is a minor phase in some cements, and has the potential to transition from an insulator to a conductor. Both of these materials can be optimized by inserting impurity ions into their regularly ordered crystal structures (i.e. doping). Tricalcium silicate is commonly doped with magnesium, aluminum, and iron naturally occurring in cement, while mayenite can be made conductive by doping with copper. This research uses density-functional theory, a quantum mechanical modeling tool, to optimize the reactivity of tricalcium silicate, and the conductivity of mayenite. Results provide a means to intelligently design new cementitious ceramics which are better performing, more easily processable, and more versatile in their potential applications.