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.
Modeling of Monosized Sphere Packings into Cylinders
Modeling of a monosized sphere packing in a cylindrical container of a fixed diameter is a frequently discussed subject in recent researches. It is motivated by the high applicability of these models, particularly by the advances in nanomaterial science and engineering, associated with the development of hierarchically ordered matters of specific structures and properties. These features strongly depend on the arrangement and density of the filling atoms in the channels of a nanostructured porous matrix. A special interest is devoted to a dense random packing, which by its nature is not totally random when the spheres do not overlap. In this paper, related models of packing are classified basing on the space filling method, and the densities reached theoretically as well as experimentally for those classes are given. The effects produced by some parameters on the packing density and the main properties are analyzed. The experimental techniques and computer modeling approaches are summarized.
Concrete for long-time service in sulfate environment
Abstract Data on concretes soaked continuously in a 2.1 percent sodium sulfate solution and alternately soaked and dried served for predicting service life. Sixteen out of 19 concretes made with Type V and II cements showed life expectancies of less than 50 years. Concretes containing different pozzolans showed a spectrum of effects ranging from deleterious to highly beneficial. Only 6 out of 33 pozzolan concretes had life expectancies of less than 50 years. Fly ash, pumice, and two calcined products markedly improved sulfate resistance. Seven of 11 concretes having a life expectancy in excess of 100 years, some possibly up to 200 years, contained fly ash. Revision of present day specifications for sulfate resisting concrete is recommended.