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.
Demonstration of Electro-Osmotic Pulse Technology for Groundwater Intrusion Control in Concrete Structures.
Abstract : Groundwater intrusion through a building's foundation (i.e., a "wet basement problem") can cause serious damage that is expensive to correct. In older buildings, such as those common on U.S. Army installations, severe damp-basement problems call for immediate action to mitigate water damage. Electro-osmotic pulse (EOP) technology offers an alternative to the "trench and drain" approach that can mitigate some water-related problems from the interior of affected areas without the cost of excavation. The EOP alternative can further mitigate corrosion damage to mechanical equipment along with humidity and mold problems. This study demonstrated and document the effectiveness of EOP technology to control groundwater intrusion in concrete structures at Fort Jackson, SC and McAlester Army Ammunition Plant (AAP), OK. The cost of installation was determined to be 40 percent lower than the cost of the conventional trench and drain approach. The operating or energy cost of the EOP system was shown to be negligible - equivalent to the expenditure of burning a 60W light bulb.
Transmission electron microscopy of lattice planes in human alveolar bone apatite crystals
SummaryPeriodic fringes corresponding to six different lattice planes have been observed in apatite crystals of human normal alveolar bone by transmission electron microscopy. Three of these sets of fringes have spacings less than 3.5 Å corresponding to the Scherzer resolution of the microscope used. The (0002) lattice plane of hydroxyapatite of 3.4 Å d-spacings, the
$$\left( {21\bar 11} \right)$$
 lattice plane with a d-spacing of 2.81 Å, and the
$$\left( {30\bar 30} \right)$$
 lattice plane with a d-spacing of 2.72 Å have been identified. The (0002) and
$$\left( {21\bar 21} \right)$$
 lattice planes have been observed for the first time in bone microcrystals. Some of the crystals studied were characterized by a mean width/thickness ratio of 6.91, typical of platelike habit, whereas observations of crystals aligned along the
$$\left\langle {1\bar 210} \right\rangle $$
 and
$$\left\langle {1\bar 211} \right\rangle $$
 directions showed a needlelike habit. The mean length of the bone apatite crystals was 470 Å. A dark line similar to the one observed in enamel and dentine crystals was also seen. The bone microcrystals observed have shown a high sensitivity to beam damage.