The paper tried to evaluate the performance of anode embedded in concrete regarding with the impressed current system. Accelerating impressed current was applied between anode and cathode within short period, in which the accumulating current density corresponded to the period of 40 years. The specimens were soaked under water because of lower concrete resistance. The instant-off potential of titan-mesh anode remained comparatively higher than that obtained based on NACE, but was within 4.0V and satisfied NSCE. Moreover, it was inclined that instant-off potential increased in the state of logarithm curve under the condition of constant applied current. After the accelerating impressed current test, it was proposed to carry out the anode polarization test so as to evaluate in detail the performance change of anode materials. And it was clearly shown that there was no degradation of adhesion between concrete and overlay after the severe accelerating test. Furthermore, the quality change of concrete surrounding anode materials was made clear by way of chemical analysis.
This research was conducted to develop a model to estimate the effective diffusion coefficient of substances in concrete considering with spatial properties of each composition material. In this model, concrete was assumed to be composed of cement paste, interfacial transition zone and aggregate. Proposed model could appropriately evaluate the effective diffusion coefficient of chloride ion in concrete in previous research. The influence of spatial properties of each composition material on the dispersion of effective diffusion coefficient of chloride ion in concrete was investigated. The influence of cement particle arrangement on the dispersion was larger than that of aggregate arrangement, and that influence became remarkable as W/C became low. Moreover, in the calculation of the effective diffusion coefficient of concrete, when the change in pore volume was considered without considering microstructure development in detail, an annronriate value may be obtained with a reasonable accuracy.
We study the expansive concrete filled steel tube with a flat bar in center using for a brace member of the energy dissipative braced frame. The test results of the chemical prestress of this tube with a flat bar in center may be summarized as follows : (1) The concrete with Water/ (Cement + Silica fume + Expansive admixture) =25-30% and Ex/ (C+S+Ex) ≥50% has a very high expansive capacity. (2) Ratio of the tangential normal stress to the yield stress of the steel tube at yield of it is about 1.15. (3) Ratio of the axial normal stress of the flat bar to the axial normal stress of the tube at yield of it is 0.15 0.45. (4) Ratio of the axial normal stress to the tangential normal stress of the tube at yield of it is 0.4-0.5. From the above results, We proposed the estimate formulae for the prestress of the expansive concrete in the tube with a flat bar in center at yield of the tube.
Recently, many cases of initial flaws, damage and deterioration of road bridge slabs have been reported. Securing the heat source and detection and evaluation of changed sections by the thermography method are problems, however, because slab bottoms are shaded and temperature differences from changed sections cannot be anticipated. We studied the relationship of internal flaws and surface temperatures using the pavement heat of asphalt improvement work. As a result, surface temperature distribution corresponding to flaw slopes was confirmed in the heat image from pavement heat transfer, making it possible to detect internal flaws and flaws in contact with surfaces. The effectiveness of using pavement heat is clarified through comparison with the passive method and the three dimensional unsteady heat simulation.
Current punching shear capacity equation of reinforced concrete slabs with the normal concrete excessively estimates the punching shear capacities of reinforced concrete slabs with the lightweight concrete. In this study, material tests and dowel capacity tests of using the lightweight concrete were conducted to make clear the punching shear failure condition of reinforced concrete slabs with the lightweight concrete. Dowel capacities of reinforced concrete beams using the lightweight concrete decrease due to the weakness of its aggregate in comparison with those using the normal concrete. From the test results, the predicting equation of the punching shear capacities of reinforced concrete slabs with the lightweight concrete was proposed. This equation can accurately evaluate the punching shear capacities of reinforced concrete slabs with the lightweight concrete as well as the fiber reinforced lightweight concrete. And the fatigue durability of reinforced concrete slabs with the lightweight concrete was assessed based on the existing data conducted under the wheel running machine. Furthermore, slab thickness and dead load ratios of the reinforced concrete slab with the lightweight concrete were calculated to confirm its practical use.
This paper presents a limit displacement under compressive axial force of R/C columns using high strength concrete up to 160MPa and high strength steel. Based on 115 test data, equations of the limit displacement were proposed. Main factors of the equations are axial force ratio, amount of lateral reinforcement, yield strength of main bars, loading type of axial force (constant or varied) and concrete strength. The effect of buckling of the main bars and a shape of the lateral reinforcement are also included.
Over 30 years have passed since the expanding material for the concrete is developed in Japan, but it is hard to be said that the expanding material is widely used. In the inside where the durability of the concrete becomes a problem, the expansive concrete is being reexamined as one of the promising techniques which suppress the crack. In the meantime, expanding material has positively been used on the concrete product for the purpose of the chemical pre-stress introduction in order to raise the external pressure strength. Here, methods for coordination on new-model expanding material which added the performance which obtains early age strength was examined for the purpose of reduction of steam curing energy, improvement of mould rate of rotation and the prevention of crack. In addition, it was confirmed that the fast-strong performance of the new-model expanding material was well obtained as a result of applying to actual concrete product. As to this mechanism, it was considered that it was in early hydration heat build-up state of the new-model fast-strong type expanding material and hydration promotion of the alite of the cement.
The best way to investigate the tension softening process is by applying a uniaxial tension force directly on a concrete specimen, because it can measure both tensile strength and the tension softening curve from an identical specimen. However, no standard tests have been adopted to provide a direct measurement of the tension softening curves of concrete, though many inadequate test procedures were proposed until recently. There are four misunderstandings in investigating the tension softening process, concerning the effects of notches, secondary flexure, boundary conditions and specimen geometry. In this paper, the misunderstandings are discussed and clarified in detail with theoretical and experimental considerations. A test procedure free from these misunderstandings is proposed for the uniaxial tension test of concrete and some successful test results are presented.
Three-dimensional particle size distributions of unhydrated cement in cement paste were obtained from its two-dimensional cross sections by the stereology analysis. The mean diameter of the unhydrated cement particles was used for determining the degree of hydration of cement. The degree evaluated by the average diameters was consistent with those determined by the volume fractions of unhydrated cement and non-evaporable water contents. It was also possible to determine water/cement ratios of hardened concretes, using the hydration degree based on the average diameters and the volume fractions of unhydrated cement particles in concrete at a given age. The particle size distribution of unhydrated cement can be a characteristic feature reflecting the process of hydration of cement.