Measurement and Modeling of the Ability of Crack Fillers to Prevent Chloride Ingress into Mortar.
A common repair procedures applied to damaged concrete is to fill cracks with an organic polymer. This operation is performed to increase the service life of the concrete by removing a preferential pathway for the ingress of water, chlorides, and other deleterious species. To effectively fulfill its mission of preventing chloride ingress, the polymer must not only fully fill the macro-crack, but must also intrude the damage zone surrounding the crack perimeter. Here, the performance of two commonly employed crack fillers, one epoxy, and one methacrylate, are investigated using a combined experimental and computer modeling approach. Neutron tomography and microbeam X-ray fluorescence spectrometry (μXRF) measurements are employed on pre-cracked and chloride-exposed specimens to quantify the crack filling and chloride ingress limiting abilities, respectively, of the two polymers. A two-dimensional model of chloride transport is derived from a mass balance and solved by the finite element method. Crack images provided by μXRF are used to generate the input microstructure for the simulations. When chloride binding and a time-dependent mortar diffusivity are both included in the computer model, good agreement with the experimental results is obtained. Both crack fillers significantly reduce chloride ingress during the 21 d period of the present experiments; however, the epoxy itself contains approximately 4 % by mass chlorine. Leaching studies were performed assess the epoxy as a source of deleterious ions for initiating corrosion of the steel reinforcement in concrete structures.
MODELING CHLORIDE TRANSPORT IN CRACKED CONCRETE --- A 3-D IMAGE-
The prediction of concrete materials service life is not easy, because the complex heterogeneous microstructure and the random nature of concrete materials. Study the presence of cracks in concrete and their effect on coupled reaction and transport are of great interest in civil engineering. Cracks with different widths and depths will reduce the cover thickness and accelerate the migration of chloride ions. So, it's highly desirable to develop a model to predict the chloride diffusion depth in cracked concrete while considering the real microstructure including cement, voids and aggregate. While current models consider a variety of concrete at varying levels of complexity, predicting the initiation of chloride-induced corrosion, considering the influence of cracking is generally beyond their scope. Previous research has used COMSOL Multiphysics to investigate the microscale corrosion of reinforced concrete cracking due to non-uniform corrosion (Pan and Lu 2012). The cracked and porous media was analyzed by COMSOL (Perko et al.). Reaction and diffusion processes were also studied by (Richter et al.). Digital image analysis was used to represent rock structures (Zhang et al.). In this study, the 3D image-based microstructure was provided by the advanced mathematical representation of random microstructure (Lu and Garboczi). Next, a 3D mesh representing true multiphase microstructure was written in Nastran mesh and imported to COMSOL Multiphysics. Two COMSOL interfaces, Transport of Diluted Species and User Defined ODE Mathematics, were employed in this study to examine the influence of cracking on chloride penetration into concrete. Moreover, we use COMOL to assign boundary conditions directly on 3D mesh, rather than on the geometry. Eventually, predicting the chloride penetration in heterogeneous microstructure of concrete can be accurately simulated with COMSOL Multiphysics. The chloride concentration gradient existed in the crack obviously, and it changed the chloride concentration along the crack and irregular aggregate surfaces continually. Comparison to experimental data indicates that the contributions of binding of the chloride ions by the cement paste play a significant role in slowing the ingress of chlorides and should be accounted for in any modeling efforts.
The denial of death and the out-of-the-body experience
The out-of-the-body experience is a phenomenon which continues to be reported and continues to be interpreted in many ways. It seems, however, that more attention is given to finding a spiritual base for this occurrence than a psychological understanding of it. This paper considers the psychological forces of denial as a suitable explanation for the OBE and suggests that these experiences may be understood as hallucinations caused by traumatic events rather than genuine previews of the afterlife. That is: “Do these people transcend their bodies and also time and space to acquire these experiences, or could it be that nothing has been transcended at all save the need to deny death and thus transcend its feared consequence, which is ‘not being’?”