In this study, damaged areas of RC beams failed in shear compression were experimentally evaluated by means of acrylic lattice method which can measure planar strain distribution. Three-dimensional nonlinear finite element analysis was also conducted in order to verify the damage evaluation method and failure criteria of RC members failed in shear compression. As the result, damage region were evaluated by the averaged strain without mesh dependency and failure criterion for shear compression failure was proposed. It was confirmed that the proposed method was also applicable to RC beams, which has various dimension and specification, failed in both shear and flexural by the analyses. Moreover, it was shown that the proposed criterion was useful to evaluate the damage of a member in statically indeterminate structures.
A part of cover concrete in the slab at road bridges may exfoliate by the chloride induced deterioration. These dangerous concretes are knocked down because of the prevent for the hazards for third party. Therefore, the rust inhibitor with the zinc to the exposed rebar is treated. However, re-degradation occurs, when chloride ions remain in the base concrete. Based on the above backgrounds, this study proposes the method to reduce the re-degradation by the increase of the electrical resistance between the knock down part and the base concrete using silane type penetrants. First, feasibility studies are conducted using mortar and concrete specimens. Next, the test is conducted using slab cut from the road bridge. It can be confirmed that the after the knock down is decreased for about 6.5 year. As a result, the method proposed in this study is effective as the emergency treatment for the slab with chloride induced corrosion.
The pit filler material of the underground cavern-type radioactive waste disposal facility, which is poured directly around the radioactive waste packages where high temperature environment is assumed by their decay heat, is concerned to be adversely affected on the filling behavior and its hardened properties. There also are specific issues that required quality of construction must be achieved by unmanned construction with remote operation, because the pit filler construction shall be done under radiation environment. In this paper, the mix proportion of filler material is deliberated with filling experiments simulating high temperature environment, and also the effect of temperature on hardened properties are confirmed with high temperature curing test. Subsequently, the feasibility of unmanned construction method of filler material by pumping, and by movable bucket, are comparatively discussed through a real size demonstration.
It is known that the shear strength of a member with a T-shape or hollow rectangular cross section is greater than the value calculated by the shear strength calculation method in accordance with the current standard. This study examined a method for calculating the shear capacity value closer to the actual value by conducting a shear test of a RC beam having such a cross section. Since the test result showed that a diagonal crack occurred in the web of a member before its flange was failed, a calculation method was verified by adding the shear strength of the flange to that of the rectangular part of the cross section. As a result, it was confirmed that this method calculates the value closer to the actual shear strength compared with the currently used shear strength calculation method.
To gain a more direct insight into nature of water in contact with calcium silicate hydrate (C-S-H), the main component of hardened cement, deuterium (2H or D) quadruple echo NMR (nuclear magnetic resonance analysis) spectra, deuterium relaxation time T1 and rotational correlation time τc were determined from white Portland cement and 2H2O mixtures subjected to different relative humidity curing conditions, (RH) 98, 60, 33 and 11%, for 91 days. The 2H NMR spectra shows two signals: a sharp central signal at 0 kHz and outer symmetric signals around ±100 kHz. The central signal is considered to belong to mobile deuterium and the outer symmetric signals are considered to belong to immobile deuterium. The strength of the central signal decreases with increasing curing RH, but even the RH 11% sample has shows a signal strength that indicates the existence of both mobile and rigid deuterium in the sample. The study on relaxation time T1 and rotational correlation time τc indicates that the signal of central signal contributes the mobile state deuterium can be distinguished into two different components by τc: a faster τc component is comparable to the liquid state and a slower τc showing restricted movement of the water. Previous studies have shown two water states near the surface of pores in C-S-H; one is a single-layer of adsorbed water like on the surface of protein and the other is a several layer thick ‘semi-adsorbed’ water layer around the absorbed water. Further, the water generating the slower τc value could belong to such adsorbed water and the faster τc value could be assigned to semi-adsorbed water. These results will help to describe and evaluate the structure changes of C-S-H induced by the relative humidity at curing.
Analytical evaluation of crack propagation of reinforced concrete beam was performed. Creep, shrinkage, change of material characteristics depending on hardening and bond behavior were considered in 3-Dimensional finite element analysis. Crack initiation and crack width on increasing load were evaluated considering bond behavior. Time dependent propagation under constant load such as curvature and crack width was also evaluated for normal and high strength concrete. Moreover, the effect of dry shrinkage, autogenous shrinkage, creep and area of shrinkage in beam on crack propagation were investigated.
The influences of concrete temperature with ground granulated blast-furnace slag on the autogenous shrinkage and on shrinkage stress are experimentally investigated. By measuring the autogenous shrinkage and shrinkage stress caused by restraint of reinforcement bar under different curing temperatures of concrete with ground granulated blast-furnace slag and of concrete ordinary portland cement, it is clearly shown as follow. Although the variation of autogenous shrinkage of ordinary portland cement concrete due to temperature changes is less, that of blast furnace cement concrete depends notably on the concrete temperature. Moreover, as a result of calculating reduction constant for modulus of elasticity based on the shrinkage stress, reduction constant of blast furnace cement concrete is larger than that of ordinary portland cement concrete under the condition of high concrete temperature.
This paper reports on an experimental study regarding the behavior of restrained high-strength concrete in response to the type of extreme heating associated with fire. This study was intended to support estimation of thermal stress from the strain in a restraining steel ring and vapor pressure in restrained concrete under the conditions of a RABT 30 rapid heating curve. Thermal stress calculation was based on thinwalled cylinder model theory. It was also suggested spalling failure model was based on strain failure model. In a results, the model can be estimated the point at which the spalling started and spalling depth during heating.
In this study, mass transport models in multi-scale thermodynamic analytical system were enhanced focused on the nano-meter-scale phenomena with the purpose of reproducing high resistivity against chloride attack with the low W/C concrete materials and studying its causes. Based on the results of sensitivity analyses and past researches, modified water amount considering the threshold radius about chloride ion movement was introduced in the chloride ion transport model, and also friction force between pore wall and pore water was installed to the water permeability coefficient in the liquid water transport model. Proposed model was verified with the results of salt water immersion tests and the analytical results showed that enhanced models reproduced the high resistivity against the chloride ion penetration in the low water-to-cement ratio materials properly.
A performance verification experiment of cavern type radioactive waste disposal facility with a real scale construction is being conducted to evaluate the applicability of proposed construction methods and construction quality of the facility. In this paper, we confirmed that the low-diffusion layer, which is one of the cementitious materials based members, could be filled with mortar from end to end of the member; cracks of low-diffusion layer would not affect the long-term safety evaluation of the facility. And also we figured out the relationship between the material strength and the accumulated temperature, relationship between diffusion coefficient and porosity of low-diffusion layer.