jimmy choo south africa vwi bio jqlh hib

asbryobvrz

Stress Analysis of Concrete with surface

Paper Keywords: old; combination; analysis Abstract: Whether the project has been built reinforcement,[link widoczny dla zalogowanych], repair or new construction, often encountered in the concrete has hardened or has been chiseled deterioration, shortening some of the solid concrete exposed Primary pouring new concrete or mortar on the issue. The combination of old and new concrete surface is a weak link, the interface bond strength is generally lower than the overall strength of poured concrete, which greatly affect the reliability of the structure of its analysis of the force of great significance. People old and new concrete interfaces than the corresponding bond strength of the whole reason for the strength of poured concrete is not very clear, need to be explored. Obviously, for the old concrete adhesive root of the problem solving needs of the microstructure from the perspective of concrete bonded to clarify its mechanism,[link widoczny dla zalogowanych], the establishment of micro-and macro-structure of the link between the mechanical properties, will help us to understand the new and old concrete from the nature bond issues, in order to find solution to the problem. First, the interface transition zone is mainly composed of the existence of interface region C-S-H gel (CSH), C-H crystal 〔Ca (OH) 2〕, AFt (ettringite) and unhydrated clinker particles and holes, cracks. C-H in the interface region more than the number of transistors and a larger crystal size, while holes in the interface area is large, the interfacial bonding will be adversely affected. II formation mechanism of interfacial transition zone in the concrete mixing process, in aggregate surface layer several microns thick water film,[link widoczny dla zalogowanych], while the density of anhydrous cement aggregate at the close almost zero, and then increased as the distance increases. Therefore, in this layer of water film that basically does not exist in the cement particles. When the cement compounds dissolved in water, the dissolved ions that diffuse into this layer of water film. If it is insoluble aggregate, all the ions from the water film of cement clinker and gypsum. However, if the aggregate is partially soluble, the aggregate of the dissolution of the ions in the aggregate surface density. Because there will always be part of the ion aggregate precipitation, the highest concentration near the aggregate surface, since there is a significant defect that the low concentration area. Therefore, in this layer of water film, the first nuclei to form hydration products is the first ion diffusion into the water film of ordinary portland cement is calcium hydroxide, ettringite and stone. Hydrate crystals within the water film is formed in the nucleation and growth in solution, due to saturation of the membrane is not too high, there is ample space for crystal growth, so the formation of larger crystal size of hydration products, the formation of The network structure is more loose, less active after the aluminum ions, silicon ions have moved into the first gap left by the crystal, gradually formed C-S-H and the small size of secondary ettringite and calcium hydroxide During the stone fill. Marceau The ion concentration profile assumed in depression may be the formation of large nuclei and high porosity, is the interface the weak areas. Interfacial transition zone of low intensity, is apt to cause cracks, and cracks easily spread, so that the interfacial transition zone as the weakest link. The interfacial transition zone structure is a significant enrichment of C-H and produce crystal orientation, crystal average size larger,[link widoczny dla zalogowanych], the larger pore size and pore rate, the interface of a large number of defective loose network structure. Although many factors determine the nature of the interface, but C-H orientation and enrichment weak layer interface is the primary form of physical chemistry one of the reasons that it indirectly reflects the pore structure of the interface layer and density. Therefore, to enhance the interface region is to strengthen the weakest level in particular, to eliminate and reduce the boundary layer and the substrate the difference between the need to reduce C-H content, disruption to its orientation and reduce porosity. Third, new and old concrete interfaces weak because the force in the same conditions, the combination of old and new concrete poured than the whole surface of aggregate and cement interface, the system still weak, are the following reasons: ( 1) There is a new and old concrete is similar to the contact interface of Cast in concrete, aggregate and interfacial transition zone between cement paste, and this transition zone has always been a weak link. Hydrophilicity of the old concrete to repair the old concrete surface when the water film is formed, so that combined with the new concrete surface at the local water-cement ratio higher than the system in the water-cement ratio, resulting in interface ettringite and calcium hydroxide crystals in number and form larger, the formation of preferred orientation, reducing the interface strength. And the concrete barriers of the old and new concrete in the bleeding and air bubbles accumulate in the old concrete surface, new concrete not only makes the local water-cement ratio higher, but also make the pores and micro-crack accumulation in the area, significantly reduce the interface strength. This is the physical structure of chemical reasons, is the combination of old and new concrete the nature of internal factors. (2) interface exposed stone, cement, and new concrete poured concrete and the whole interface of aggregate and cement paste in contact with the interface differences. We know that water slurry itself has a certain bond, which is mainly used for wrapping concrete aggregate, so that hardened into a hard cement. In the new concrete aggregate after full mixing, cement vibrator has been wrapped, and the interface of old and new concrete aggregate in new concrete vibrator may be extruded through the interface, the interface is to highlight the stone aggregate and cement Stone form a cement interface of aggregate and cement paste can not be fully infiltration, loss of part of the new concrete slurry, which makes the new bond interface voids in concrete, affecting old and new concrete bond strength. (3) Cast in concrete aggregate small, multi-angular, aggregate surface roughness, so that cement can be embedded solid surface pits in the aggregate, the mechanical occlusion of the macro-bond strength plays a major role. From the microscopic point of view, it increases the effective contact area, bond strength will be greatly increased. Concrete repair materials and the old differences between the physical and chemical properties, due to alternating hot and cold, freeze-thaw cycles and new concrete surfaces at the shrinkage in the combination of the additional stress, induced From the perspective of the force, pouring concrete aggregate in the whole small, multi-angular, aggregate surface roughness and is separate from cement, distribution is more high probability, coupled with the interface more carrying capacity of new and old concrete interface will be further weakened,[link widoczny dla zalogowanych], leading to destruction of the interface first, that destruction is always the weakest link from the start.