Modeling and Simulation of Electromutagenic Processes for Multiscale Modification of Concrete
Concrete contains numerous pores that allow degradation when chloride ions migrate through these paths and make contact with the steel reinforcement in a structure. Chlorides come mainly from the sea or de-icing salts. To keep the reinforcement from being exposed to chlorides, it is possible to electrokinetically force nanoparticles into the pores, blocking access. This procedure is called electrokinetic nanoparticle treatment. When the particles used are reactive in nature, the process becomes both structural and chemical in nature. We use the term electromutagenic processing to describe such extensive electrochemical remodeling. Filling the pores in a block of concrete with solid materials or nanoparticles tends to improve the strength significantly. In this paper, results obtained from modeling and simulation were aimed at multi-scale porosity reduction of concrete. Since nanoparticles and pores were modeled with spheres and cylinders having different sizes, the results were compared with traditional sphere packing problems in mathematics. There were significant differences observed related to the sizes of spheres and allowable boundary conditions. From traditional sphere packing analysis the highest porosity reduction anticipated was 74%. In contrast, the highest pore reduction obtained in this work was approximately 50%, which matched results from actual electrokinetic nanoparticle treatments. This work also compared the analytical and simulation methods used for several sizes of nanoparticles and pores.
Dynamics of Solvated Chloride Inhibition by Nanoparticle Treated Concrete
Corrosion of steel reinforcement in concrete is caused largely by ingress of chloride ions from deicing salts and coastal marine environments. Electrokinetic nanoparticle treatment concurrent with electrochemical chloride extraction have been employed to minimize chloride attack and reinstate the passivity of embedded steel. Additionally, pozzolanic nanoparticles such as aluminumand silicon-containing materials can be injected into concrete pores using externally applied electric fields in order to reduce permeability of chloride ions into concrete. We present results of computational simulations used to investigate dynamics of solvated chloride anion (Cl ) through a tricalcium silicate nanopore in the presence of alumina (Al2O3) and silica (SiO2) nanoparticles that form the main binder phase of Portland cement. First, equilibrium properties of Cl(H2O) system are explored, using Density Functional Theory with-localized GGA exchange correlation functional of PW91. Microsolvation conformers are thus obtained as a gradual approach to bulk solvation structures. Cl atomic size is explored using radial distribution functions (RDF). Molecular Dynamics in the canonical ensemble is used to obtain coefficient of diffusion of solvated Cl at 25 °C. Diffusivity calculated from the variation of the mean square displacement of the chloride ions with time show considerable differences depending on their position with respect to nanoparticles. Increase in ion size after solvation and its diffusivity obtained implicate both solvation structure and alumina-silica nanoparticles as controlling factors for Cl dynamics in aqueous systems inside concrete pores.
“To those who choose to follow in our footsteps”: making women/LGBT+ soldiers (in)visible through feminist “her-story” theater
Building on Judith Butler ’ s understanding of visibility as “ the object of continuous regulation and contestation, ” art/aesthetics studies in international relations, and feminist theater studies, we identify feminist “ her-story ” theater as a unique site where Western “ gender-/sexuality-inclusive ” soldiering is visibilized, contested, and subverted. Drawing on ethnographic observations of two award-winning dramas, interviews with artists and military hosts, and ﬁ ndings from a wider research project on contemporary British military culture, we reveal the key role of heteronormative and patriarchal cultural discourses in reproducing the ambivalent positionalities of women/LGBT+ soldiers. We argue that the very visibility of women/LGBT+ soldiers on the stage paradoxically operates to make the complexities of – and struggles against – masculinized heteronormative military cultures invisible. Furthermore, despite artists ’ attempts to dissociate empowerment through soldiering from the problematic context of modern con ﬂ icts, “ her-story ” theater ultimately entrenches gendered/racialized hierarchies that normalize Western military interventions. We conclude that only through sustained feminist re ﬂ ection on the contours of “ imagined ” futures of female/ LGBT+ soldiering can this persistently problematic (in)visibility be productively disrupted.